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fundamentals of
, \U«IV OH ILLINO - , .. - I CHAMPAION I JI J. IP"""
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L I B R.AFIY
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BY
LESLIE A. BRYAN KERMIT B. ANDERSON I. BURNELL APPLEGATE OMER BENN EUGENE L. HAAK JAMES M. HANCOCK FRANCIS B. SCHABER H. S. STILLWELL W. DALE TRULOCK
fundamentals of
AVIATION AND SPACE TECHNOLOGY
1964 Reprint
INSTITUTE OF AVIATION • 3\B CIVIL ENGINEERING HALL • UNIVERSITY OF ILLINOIS • URBANA, ILLINOIS
© J959, 1962, 1964, by the Institute of Aviation of the University of Illinois Manufactured in the United States of America Library of Congress Catalog Card No. 64-23260
Foreword
In 1945 Mr. Edwin A. Link, inventor of the Link Might trainer and electronic simulators, and his company. Link Aviation, Inc., sponsored the publica- tion of a book written by Norman Potter and William J. Konicek of the Link staff. The book was called "Fundamentals of Aviation" and was an immediate success. Since that first publication, Mr. Link has signally benefited aviation by establishing The Link Foundation, which is dedicated to the advancement of education and training in aeronautics.
In 1955 the staff of the Institute of Aviation of the University of Illinois revised the book. It was com- pletely rewritten and enlarged in 1959 by those mem- bers of the University staff whose names appear as co-authors on the title page and the title was changed to "Fundamentals of Aviation and Space Technology."
The interest of The Link Foundation and Dr. Frank E. Sorenson, then Executive Secretary of the Founda- tion, and of Miss Marilyn C. Link, made the 1959 edition possible. However, the authors had complete freedom in the selection of materials and assume sole responsibility therefor.
Mr. James NT Hancock acted as coordinator. Mr. Robert L. Ayers, Mr. Thomas H. Bailey, Mr. Hale C. Bartlett, Mrs. Gertrude A. Becker, and Mr. Thomas H. Gordon, also of the Institute of Aviation staff, contributed materially to the manuscript.
The reception accorded the first edition of this book under its present title was very gratifying. It appealed ^especially to teachers and students, as well as to the air transportation industry for orientation courses.
The book was reprinted in 1962, with a few revisions being made to update and clarify the content, and a chapter added on developments in space explora- tion. The continued success of the book has again exhausted the supply, and a new printing is necessary only two years after the previous revision. Statistics and other items have been updated and the glossary expanded. Also, the chapters on the Federal Aviation Agency and Space Exploration have been revised to reflect recent changes and developments. For the benefit of libraries and others who wish hard covers, the book is available in such covers.
It is a pleasure to acknowledge again the coopera- tion of The Link Foundation, particularly of Miss Marilyn Link, Executive Secretary, and Dr. Frank E. Sorenson, Chairman of the Technical Assistance Board. Mr. James M. Hancock, who is now Execu- tive Director of the Chicago Planetarium Society, has acted as coordinator of the revision. Their assistance has been invaluable.
As Mr. Link wrote in the first edition of the book, "With a full realii;ation of the wide influence of aviation on the peoples of the world; with an under- standing of the problems which youth will face grow- ing up in the air age; and with a profound belief in, and respect for, the processes of education meeting this challenge, we respectfully dedicate this aviation publication to all American youth."
Leslie A. Bryan Lhhana, Illinois Director, Institute of Aviation
June 1964 University of Illinois
Contents
CHAPTER 1 LIVING IN THE AEROSPACE AGE 1 The Economic Aspect 1
Aerospace Manufacturing Industry 2
Air Transport Industry 3
General Aviation 6 The Social Aspect 6
Population Distribution 7
Education 7
Family Life 7 The Political Aspect 7
Military Operations 7
International Affairs 8
Politics 9 Summary 9
CHAPTER 2 HISTORY OF FLIGHT 1 1 Balloons and Gliders 1 1 Experiments of the Wright Brothers 1 2 Man's First Flight 13 Later Developments 1 3 Air-Mail and Air-Passenger Transportation Summary 1 4
CHAPTER 3 THEORY OF FLIGHT 16 Shape of the Wing 16 Speed of the Wing 16 Lift and Angle of Attack 17 Lift and Weight 17 Thrust and Drag 1 7 Inherent Stability 18 The Axes of Rototion 1 9 Rudder 19 Elevators 20 Ailerons 20
Coordination of Controls 20 Trim Tabs 20 Summary 22
CHAPTER 4 AIRCRAFT 24
General Structure of an Airplane 24
Wings 26
Fuselage 27
Tail Assembly 27
Landing Gear 29
Powerplants 30
Propellers 30
Jet Propulsion 31
Airplane Accessories 32
14
Other Aircraft Types 32
Aircraft Construction 34
Aircraft Inspections 34
Supersonic Transport 36 Summary 36
CHAPTER 5 THE AIRCRAFT ENGINE 38
Aircraft Engine Requirements 38
Aircraft Engine Types 39
Aircraft Engine Parts 39
The Four-Stroke Cycle Principle 40
Engine Systems 42
Fuel and Induction System 43 Ignition System 44 Accessories 44
Power Factors 45
Modern Powerplants 45 Compressors 48 Combustion Chambers 49 Turbines 49 Exhaust Cones 49 Thrust Versus Power 49 Turbojet, Turboprop, and
Turbofan Engines 50 Rocket Propulsion 50 Atomic Propulsion 51
Summary 51
CHAPTER 6 AIRPLANE INSTRUMENTS 52
Pitot-Static Tube 52
Venturi Tube 53
The Airspeed Indicator 53
The Altimeter 54
Rote of Climb Indicator 55
The Magnetic Compass 55
Tachometers 56
Magnetic Tachometer 56 Electric Tachometer 57
Oil Pressure Gage 57
Oil Temperature Gage 57
Turn and Bonk Indicator 58
The Directional Gyro 59
The Gyro Horizon 60
Summary 61
CHAPTER 7 FLIGHT TECHNIQUE 62
Airplane Attitude and Controls 62 Controls 62 Straight and Level Flight 62
The Climb 63
The Glide 63
The Turn 64
Use of Rudder in a Turn 65
Overbanking Tendency 65
Loss of Vertical Lift 65
Rate of Turn 65
Slipping and Skidding 65 The Takeoff 67 Landing Approach 67 Sumnnary 69
CHAPTER 8 AIR NAVIGATION 71 What Is Navigation? 71 Forms of Air Navigation 71 Position, Direction, and Distance 72 Maps and Charts 74 Plotting a Course 76 V/ind Drift Correction 78 Pilotage Navigation 79 Dead Reckoning Navigation 79 Radio Navigation 80 Celestial Navigation 85 Summary 85
CHAPTER 9 METEOROLOGY 86 The Atmosphere 86 Elements of Meterology 86
Temperature 87
Pressure 87
Moisture 87
Clouds 89
Circulation 90
Air Masses and Fronts 90 Elements of V^eather Important in Aviation 91
Ceiling 91
Visibility 91
Turbulence 92
Icing 93 V/eather Information Available to Pilots 94
Hourly Sequence Reports 94
Pilot Reports 94
Maps 94
Winds Aloft Reports 94
Area Forecasts 96
Terminal Forecasts 96 Summary 96
CHAPTER 10 AIR TRAFFIC CONTROL
AND COMMUNICATION 100 Air Terminal Problems 100 Aircraft Communication 100 Airport Traffic Control Tower 102 A Typical Radio-Phone Conversation 103 Air Traffic Service 105 Flight Plans 106
Typical Instrument Flight Procedure 108 Summary 1 1 0
Functions of the Federal Aviation Agency 1 12 The Deputy Administrator 113 Associate Administrators for Programs
and for Development 1 1 3 Associate Administrator for Administration 1 1 3
Federal Aviation Regulations 1 1 4
Pilot Regulations 1 15
Air Traffic Rules 1 15 Summary 1 1 7
CHAPTER 12 SPACE TRAVEL 118 The Solar System 1 1 8
Earth's Atmosphere 120 The History of Rockets 121 Current Space Problems 122
Propulsion 122
Guidance 1 23
Orbits 125
Atmosphere Re-entry 1 26
Physical Problems 1 27 Summary 1 29
CHAPTER 13 SPACE EXPLORATION Quest for Knowledge 130 Peaceful Uses 130 National Security 131 National Prestige 131 Current Space Activities 131
Explorer Satellites 131
Pioneer Satellites 132
Proiect Score 132
Discoverer Satellites 132
Transit Satellites 132
Tiros Satellites 133
Midas Satellites 133
Echo Satellite 133
Samos Satellites 133 Lunar and Interplanetary Launchings 1 34
Ranger Spacecraft 134
Surveyor Spacecraft 1 34
Mariner and Voyager Spacecraft 134 Future Space Projects 135
Meteorological Satellites 1 35
Communications Satellites 135
Observatory Satellites 135 Man in Space 1 35
X-15 Rocket Plane 135
Project Mercury 1 36
Project Gemini 1 38
Project Apollo 139 Peaceful Applications of Space Research 139
Communications 1 39
Weather 140
Additional Research Benefits 140
Summary 140 NASA's Proposed 1964 Launch Program and Official
World Records 142
APPENDIX 143
CHAPTER 1 1 THE FEDERAL AVIATION AGENCY Government Regulations 1 1 2
112
Illustrations
1 Average Annual Employment (1952-1963) 2
2 Aerospace Manufacturing Industry Sales (1951-1962) 2
3 Revenue Passengers Carried (1952-1963) 3
4 Airline, Railroad, and Bus as Per Cent of Passenger-Mile Market (1950-1962) 4
5 Hours Flown in General Aviation (1951-1962) 5
6 A North Pole Centered Map 8
7 The Wright Biplane in Flight Over the Sands of Kitty Hawk 13
8 Air Movement Around a Wing 1 6
9 Lift Increases as the Angle of Attack Is Increased 17
10 Lift Must Exactly Equal the Weight of on Airplane 1 8
11 Thrust Must Equal Drag 18
12 Pitch, Yaw, and Roll 19
13 Left Rudder Causes the Airplane to Rotate to the Left 20
1 4 Lowering the Elevators Causes the Airplane to Nose Down 20
15 Movement of the Control Stick to the Left 21
16 Trim Tabs 21
17 Airstream Action on the Rudder Trim Tab 21
1 8 Side and Top Diagram of an Airplane 23
19 Monoplane 24
20 Biplane 24
21 Various Wing Shapes 25
22 Possible Wing Locations 25
23 Internal Wing Construction 26
24 Flaps in a Lowered Position 26
25 Wing Slots Diagram 27
26 Flying Boat 28
27 Amphibian Airplane 28
28 Welded Steel Tubular Fuselage 28
29 Semi-Monocoque Fuselage 28
30 Fixed Landing Gear 28
31 Tricycle Landing Gear 28
32 Landing Gear Being Retracted 29
33 Principle of Oleo Strut Operation 30
34 1. Fine or Low Pitch 31
2. Coarse or High Pitch 31
35 Full Feathering Propeller 31
36 Propeller Pitch Performance Comparisons 31
37 Feathered and Unfeathered Propeller Performance 31
38 De-icer Boot Operation 32
39 X-18 in Flight Tests 33
40 Helicopter 33
41 Aircraft Safetying Methods 34
42 The Cockpit Section of the Link 707 Simulator 35
43 Aircraft Engine Cylinder Arrangements 38
44 Types of Crankshafts 39
45 Front View 9-Cylinder Radial Engine 39
46 Cutaway View of Twin-Row Radial Engine 40
47 Airplane Engine Cylinder Nomenclature 40
48 Valve Operating Mechanism of a Radial Engine 41
49 Stages of the Four-Stroke Cycle Engine 41
50 Radial Engine Lubrication System 42
51 A Typical Aircraft Fuel System 43
52 Cutaway View of a Turbo Supercharger 44
53 A Simplified Cutaway Drawing of a Spark Plug 44
54 Schematic Diagram of an Aircraft Engine Magneto 44
55 Typical Reciprocating Engine-Propeller Combination 45
56 Reciprocating Engine-Propeller Combination Enclosed in a Tube 45
57 Typical Turbojet Engine 46
58 Simple Rocket Engine 46
59 Schematic Diagram of a Ram Jet Engine 46
60 Schematic Diagram of a Pulse Jet Engine 46
61 Cutaway View of a Turbojet Engine 47
62 Gas Generator Section of a Turbofan Engine 47
63 Cutaway View of a Centrifugal Flow Compressor Engine 48
64 Axial Flow Compressor of Turbojet Power LJnit 49
65 Rocket Power Unit 50
66 Standard Pitot-Static Tube 52
67 Venturi Tube 53
68 The Pitot-Static Tube Connections 53
69 Altimeter 54
70 Vertical Speed Indicator 55
71 Magnetic Compass 55
72 Magnetic Tachometer 56
73 Electrical Tachometer 56
74 Oil Pressure Gage 57
75 Bourdon Tube 57
76 Oil Temperature Gage 58
77 Turn and Bank Indicator 58
78 The Gyro Assembly 58
79 Visual Indications of Various Turn and Bank Conditions 59
80 Directional Gyro 59
81 Gyro Horizon 60
82 Controls, Control Cables, and Control Surfaces 63
83 The Factors Affecting Attitude 64
84 The Aerodynamic Functions of an Airplane Wing 65
85 The Forces Acting on an Airplane in a Normal Turn 66
86 Loss of Vertical Lift in a Turn 66
87 A Skidding Turn 66
88 Traffic Patterns 68
89 An Imaginary Axis Through the Center of the Earth 72
90 Lines of Longitude 72
91 Lines of Latitude 72
92 Latitude and Longitude Lines Correspond to Streets and Avenues 73
93 Direction 73
94 A Compass Rose 74
95 Sectional Chart 75
96 Standard Symbols Used on a Sectional Chart 76
97 Method of Obtaining a Lambert Projection 77
98 Measuring a True Course Line with Protractor 77
99 Agonic and Isogenic Lines of Variation 78
100 (left) Wind Drift 78 (right) Wind Correction 78
101 A Typical Wind Triangle 79
102 Contact Flight Log 79
103 Radio Facility Chart 80
104 Radio Facility Legend 81
105 Two-Way Radio System 82
106 Directional Radio Transmissions 82
107 Part of a Sectional Chart 83
108 Automatic Direction Finder (ADF) 84
109 Aircraft VHF Transmitter and Receiver 84
110 The Atmospheric Regions 86
1 1 1 Convective Wind Currents 87
1 1 2 Principal Types of Clouds 88
113 The Theoretical Winds on an Earth of Uniform and Even Surface 90
114 Pilot's Forward Visibility in Snow Can Approach Zero 91
115 Avoiding Convective Turbulence 92
116 Surface Obstructions 92
117 Turbulent Air 92
118 Clear-Air Turbulence 92
119 Three Stages in the Life Cycle of a Thunderstorm 93
120 Rime Ice 93
121 Key to Aviation Weather Report 94
1 22 Sample Black and White Surface Weather
Map 95 1 23 Key to Report of Winds Aloft 96
1 24 Area Aviation Forecast and Interpretation 97
125 Terminal Forecasts and Interpretation 98
126 Airport Control Tower 100
127 Proper Way to Hold a Microphone 102
128 Interior of an Airport Control Tower 103 1 29 Airport Control Tower Operator
Manning a Light Signal Gun 104
130 Air Route Traffic Control Center 105
131 Table of Organization of Air Traffic Service 1 06
132 A Typical Flight Plan 107
133 A Portion of a Radio Facility Chart 108
134 Federal Aviation Agency Table of Organization 1 1 3
1 35 Minimum Safe Altitudes for Aircraft 1 1 5
136 Rights of Way 115
137 Rights of Way for Aircraft in Flight 1 16
138 Minimum Cloud Clearance Inside Control Area 1 1 6
1 39 The Solar System 1 1 9
140 Disc-Shaped Galaxies in the Southern Hemisphere 1 20
141 Liquid and Solid Fuel Rocket Engines 123
142 Conic Sections and Basic Orbits 125
143 The Satellite Ellipse 125
144 The Titan ICBM Is Launched from Cape Canaveral 128
145 The NASA Mercury-Redstone III 131
146 NASA's Satellite TIROS III 133
147 Full-Scale Model of Surveyor Satellite 134
148 Mercury Capsule 137
149 Project Mercury, Ballistic Missile 138
150 Mockup of a Project Gemini Spacecraft 139
Table 1 Aerospace Industry Classification 1 Table 2 Flying Times of Modern Jets vs. Douglas DC-7C 3
Chapter 1 Living in the Aerospace Age
No other mode of transportation has had greater im- pact on the world than aviation. None has so changed the economic, political, and social traditions of the world in such a short period of time. The phenomenal growth of the aerospace industry, the rapid expansion of commercial air travel, the tremendous influence of aviation on military concepts and international affairs, all have had inescapable and overwhelming effects on day-to-day living.
The youth of today must have an appreciation and awareness of the history, practical effect, and future potential of this transportation giant. Only through an understanding and application of aeronautical principles, by both the present and future generations, will the United States be able to maintain its air- power position. Many young Americans have already realized the value of a technical aviation education, including flight and engineering, and are well on the way to participation in the Aerospace Age. Space travel and the space frontier are absorbing and vital problems.
But just as important is an awareness of the advan- tages and disadvantages, the privileges and restric- tions, and the rewards and consequences of expanding aviation in the world of today and tomorrow. The im- pacts of aviation are economic, social, and political.
The Economic Aspect
Aviation in the United States directly influences the economic activities of millions of individuals. Several hundred thousand persons are industrially employed in the field of aviation. Millions of passengers fly on the commercial airlines each year for both business and pleasure. Both the production and the distribution of goods and services are facilitated by the airplane. Mass-production firms use air freight when production line stoppages are threatened. Increasing quantities of goods are being flown direct from factory to retail outlets, providing more rapid delivery and eliminating the need for warehouses in a firm's distribution system.
Air-mail letters move across the United States, non- stop, in approximately five hours. Even live lobsters are flown from Maine to air-conditioned supermarkets in Texas. The use of helicopters for air taxi and in- dustrial work is rapidly increasing. Businessmen are now aware of the economic value of owning and oper- ating private aircraft for business purposes. Corporate flying is growing in tremendous strides. As consumer incomes continue to grow, more and more people will own personal aircraft.
Categorically speaking, there are three basic areas in aviation; (1) the aerospace manufacturing indus- try, both civil and military; (2) the air transport in- dustry; and (3) general aviation.
Table 1. Aerospace Industry Classification
Aerospace Manufacturing Industry; Aircraft
Aircraft Engines Aircraft Parts and Accessories Missiles Spacecraft
Air Transport Industry;
Domestic Scheduled Airlines
Trunk Lines
Local Service Lines
Helicopter Airlines
Supplemental Air Carriers International and Overseas Lines Alaskan Carriers Intra-Hawaiian Carriers All-cargo Airlines
General Aviation;
Business Flying Commercial Flying Instructional Flying Personal Flying
The aerospace manufacturing industry includes all research, development, fabrication, assembly, and sales operations relating to airplanes, missiles, parts, accessories, and equipment. The industry also in- cludes major overhaul, maintenance, and modification facilities.
2 FUNDAMENTALS OF AVIATION AND SPACE TECHNOLOGY
63 (Fob.)
Figure 1 — Averoge Annuol Employment in the Aircraft ond Parts Mfg. Industry (1952-1963). Source: Aerospoce Focfs ond Figures, 1963 Edition, p. 69.
In contrast, the air transport industry encompasses only scheduled flying activities performed by com- mercial airlines and air freight carriers. The routes flown, the rates charged for services, and all items pertaining to safety are carefully regulated by the federal government.
General aviation consists of all other aviation activi- ties except those of the air transport industry and the military services.
THE AEROSPACE MANUFACTURING INDUSTRY
During World War II, the United States aircraft manufacturing industry became a large industrial complex capable of producing 100,000 planes per year. Employment soared to over 1.3 million persons. How- ever, after the war ended and enough civilian aircraft had been produced to satisfy the immediate post- war demand, the industry dropped to a point where it was producing at a rate of only 6 per cent of its
Figure 2 — Aircraft Manufacturing Industry Soles (1951-1962).
wartime capacity. With the onset of the Korean War, the industry began to expand again, and, since 1950, has grown to be one of the most important industries in the United States. In 1962, aircraft and allied manufacturing represented a $19.5 billion industry. (Figure 2.) This growth is economically significant because in ten years the industry created several hun- dred thousand new job openings— employment rose from 670,000 in 1952 to over 726,000 in 1963. ( Figure 1-)
The foundation for this employment increase and growth of the industry is the national defense pro- gram. In recent years, over 50 per cent of the federal government's budget has been allocated to national defense; of this, a significant portion has been diverted to the aerospace manufacturing industry for research, development, and production work on airplanes, mis- siles, and spacecraft. During the 15-year period 1947- 1961, 89 per cent of the total sales of 51 of the largest aerospace companies was to the federal government.
Not only is a vast number of jobs created by the industry, but a wide variety of skills is also needed.
LIVING IN THE AEROSPACE AGE
Aircraft, missile, and spacecraft manufacturing all emphasize research and development activities. Be- cause there are constant changes in design and pro- duction methods, the research and development field is an important source of employment for engineers, scientists, technicians, and craftsmen. In 1956, the amount of money spent for researc?h and development in the aerospace industry exceeded that of all other industries. Since 1957 the industry has had a higher proportion of scientists and engineers involved in research and development work than has any other industry. In addition, these scientists have more craftsmen assisting them than is the case in any other industry.
Even though professional and technical personnel are necessary, there are also many job openings for skilled and semi-skilled production workers. Approxi- mately 50 per cent of the industry's working force are tool and die makers, sheet metal workers, machine tool operators, welders, inspectors, assembly line pro- duction workers, and maintenance men.
AIR TRANSPORT INDUSTRY
October, 1958, marked the beginning of a new era in the history of commercial air transportation in the United States. During this month, a United States international carrier inaugurated the first regularly- scheduled commercial jet airliner service from New York City to Paris and soon after to London and Rome. Likewise, a major domestic airliner initiated non-stop transcontinental jet service in January, 1959. In Feb- ruary, jets began flying between Chicago and the West Coast with jet service soon following for all major cities in the United States.
The development of commercial jet airliners repre- sents the highest degree of mechanical perfection yet achieved by man in the field of public transportation. The giant four-engine turbojet aircraft are capable of carrying 100 to 150 passengers, in silent, vibration-free flight, between 500 and 600 miles per hour, at altitudes of 40,000 feet, for distances up to 5,000 miles.
The magnitude of progress in air transportation achieved since World War II becomes apparent when it is remembered that as late as 1941, air travelers were crossing the United States in two-engine, 21- passenger airliners at 165 miles per hour, requiring 16 hours to make the trip. Even when comparing the jet with its predecessor, the highly-perfected, conven- tionally-powered DC-7C commercial airliner, the dif- ference is noticeable. On the average, the modern commercial jet airliners reduce flying time between cities by approximately 42 per cent.
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61
Figure 3 — Revenue Passenger Miles Flown (1952-1963). Aerospoce Facts and Figures, 1963 Edition, p. 126, and Week and Space Technology, Morch 16, 1964, p. 164.
Source: 4v(at(on
Table 2. Flying Times of Modem Jets vs. Douglas DC-7C
|
DC-7C |
Jets |
||
|
Cities |
Miles |
(hours) |
(hours) |
|
New York to London |
3,250 |
12.0 |
6.5 |
|
New York to Paris |
3,680 |
13.0 |
7.0 |
|
New York to Rio de Janeiro |
5,020 |
18.5 |
10.0 |
|
San Francisco to Honolulu |
2,420 |
8.0 |
5.5 |
|
Los Angeles to New York |
2,458 |
7.5 |
4.5 |
|
New York to Los Angeles |
2,458 |
8.5 |
5.5 |
Economically speaking, since a jet transport can carry more people at higher speeds, it accomplishes more work in the same period of time than the con- ventional airliner. A jet transport carries twice as many passengers as a DC-7C at 1.5 times the speed; therefore, its productive capacity is three times that of the DC-7C. Another illustration of the economic importance of the jet airliner is the ability of one jet
4 FUNDAMENTALS OF AVIATION AND SPACE TECHNOLOGY
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DATA ESTIMATED
50
52
60
62
Figure 4 — Airline, Railroad and Bus as Per Cent of Domestic Passenger Mile Market (1950-1962). Source: Aerospace Facts an6 Figures, 1963, p. 129.
airliner to fly the North Atlantic route and carry the same number of passengers annually as a 40,000-ton ocean liner such as the Queen Mary.
Three factors which indicate the economic value of air transportation are: (1) revenue passengers carried; (2) revenue passenger-miles flown; and (3) the dollar volume of sales revenue. Since 1949, the number of revenue passengers carried by both domestic and international airlines has more than quadrupled. In 1949, the domestic airlines carried over 12 million revenue passengers. In 1962, over 62 million were flown. Similarly, international airlines increased from 1.5 million revenue passengers flown in 1949 to over seven million in 1963.
During this same period, revenue passenger-miles flown by the domestic trunk carriers quintupled, while the international carriers quadrupled their mile- age. In 1962, the domestic trunk airlines flew nearly 44 billion passenger-miles and in 1963 the international carriers flew 13.3 billion passenger-miles. The total
revenue passenger-miles flown by these two carriers is equivalent to ten persons each making 10,396 round trips to the moon during a single year, or more than 28 round trips each day.
In 1962, sales revenue in the air transport industry climbed to a volume of $3.4 billion.
In 1938, the airlines accounted for only 1.7 per cent of the total passenger volume, while railroads received 65.5 per cent, and buses 32.8 per cent, but twenty- five years later, air travel had increased about 25 times, while rail travel had declined over 51 per cent in relative importance. By 1962, the domestic airlines received 45 per cent of the total passenger volume; railroads, 26 per cent; and buses, 29 per cent. ( Figure 4.)
The demand for scheduled airline passenger service in the U. S. domestic market is projected to rise from about 36 billion revenue passenger-miles in 1962 to 43 billion in 1965 and to 57 billion in 1970. The trip- length distribution of this demand is expected to shift modestly toward the long haul. The coach- economy share of this demand is projected to increase markedly, from more than 55 per cent in 1962 to about 85 per cent by 1970. The development of new all- cargo aircraft and new cargo-handling systems, to- gether with more efficient carrier operating practices and keener competitive situations, should enable domestic aircargo prices to drop about 45 per cent during the 1960's. This factor, plus the projected expansion of the gross national product and the in- creased demand for airmail which seems likely, is expected to stimulate a combined demand increasing from about 510 million ton-miles in 1963 to about 2'/3 billion ton-miles in 1970.
The free world demand for international air pas- senger transportation is projected to rise from about 26 billion revenue passenger-miles in 1960 to 38 billion in 1965 and 54 billion in 1970. The U. S. flag car- riers' revenue passenger-miles are projected to in- crease from 8'/, billion in 1960 to 13.3 billion in 1963 and to about 17 billion in 1970. The coach-economy share of this demand is projected to increase from an already high share of about 75 per cent in 1960 to 90 per cent by 1965 and to 94 per cent by 1970. Predicated on the forecast that rates in the free world international aircargo market will be reduced by 60 per cent between 1960 and 1970, the free world effec- tive demand for international aircargo and airmail transportation is projected to increase to more than 5 billion ton-miles in 1970. The U. S. flag carriers' share of this demand is projected to increase from about 1.8 billion ton-miles in 1963 to about 2 billion ton-miles in 1970.
Considering the fact that only 30 per cent of the
people in the United States have ever flown, the above estimates do not seem unreasonable. A vast market of potential air travelers is still available and, further, a growing population indicates that the market poten- tial is expanding, not contracting.
In summary, the economic effects of the present air transport industry are: (1) a sharp shrinkage of distance in terms of time; (2) a greatly expanded transport capacity of the new jet in comparison to propeller-driven aircraft; (3) a tremendous increase in the number of people using air transportation for business and pleasure; and (4) a major shifting of traffic volume from the railroads to the airlines.
What economic significance will the air transport industry have on employment? In 1963, about 175,000 persons were employed in this industry, and more than 40,500 worked for the Federal Aviation Agency. In 1952, the industry employed about 98,000 people. Therefore, non-governmental employment increased about 70 per cent in an eight-year period.
Airline operations require many skilled workers to fly and maintain aircraft, provide passenger and ter- minal service, and perform long-range planning for management purposes. Pilots, navigators, flight engi- neers, mechanics, traffic agents, dispatchers, meteor- ologists, engineers, and administrators, all combine their talents to provide a properly functioning, efficient airline. In addition. Federal Aviation Agency person- nel are concerned with air traffic control, airways communications and navigational facilities, flying safety, and research and development activities. A very important and growing field within the FAA is the development of the air route traffic control system which will create new positions for radar controllers, technicians, and dispatchers.
Of the people working for an airline, about 14 per cent are flight personnel, 20 per cent are mechanics, and 2 per cent are communications specialists. The remaining 64 per cent are concerned with ticket sales, reservations control, ground servicing of aircraft, sales management, personnel administration, economic re- search, legal counsel, and executive duties.
Air Cargo
The aircargo business is conducted by two groups: ( 1 ) the all-cargo airlines, and ( 2 ) the regular domes- tic and international airlines. The all-cargo airlines were established to carry aircargo exclusively.
The volume of aircargo— freight, mail, and express —has been increasing over the years. In 1962 the total volume of cargo carried by the certificated air- lines totaled nearly 1.3 billion ton miles of which 898.1 million ton-miles was freight, over 251.4 million ton-miles was mail, and 70 million ton-miles was
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Figure 5 — Hours Flown in General Aviation (1951-1962). Source: Aerospoce Focfs ond Figures, 1963 Edition, pp. 133-4.
express. While the percentage of volume of cargo carried by air is less than one per cent of the total intercity ton-miles moved by all forms of transporta- tion, the airlines are planning on carrying much greater quantities in the future.
Air transportation costs still are high when com- pared solely with the costs per mile of water, rail, or truck transport. Today, however, by carefully analyz- ing total distribution costs, the airlines are often able to show manufacturers that standard production-line items may be shipped more profitably by air. Savings result primarily from the ability of the manufacturer to eliminate large inventories, cut warehousing re- quirements, and reduce the number of times the prod- uct must be handled. Moreover, good will is estab- lished between the manufacturer and his customer through rapid attention to and delivery of the cus- tomer's orders.
Helicopters
The helicopter is a relatively uneconomical form of transportation. It requires several hours of ground
6 FUNDAMENTAIS OF AVIATION AND SPACE TECHNOLOGY
maintenance time for every hour of flight time. It is slow and difficult to fly. Only now is it beginning to achieve all-weather operation. Further, its payload is limited when compared to that of an airplane. Yet the helicopter fulfills a very important need in com- mercial air transportation because of its small-field versatility*.
Scheduled helicopter airlines carry passengers be- tween downtown locations and airport terminals. In 1959, three cities had scheduled helicopter service- New York, Chicago, and Los Angeles. A St. Louis firm has inaugurated metered helicopter service similar to that provided by taxicabs. Even though heli- copter transportation is still in its infancy, its growth record is phenomenal. Operations began in 1953. During that year 1,000 passengers were carried. In 1962, 359,000 passengers were carried-a 359-fold in- crease!
GENERAL AVIATION
The major divisions of flying within the general aviation classification are (1) business, (2) commer- cial, including agricultural and charter flying, (3) instructional, and (4) personal. In terms of number of aircraft operated and number of hours flown an- nually, general aviation leads all other segments of civil aviation. In 1962, over 82,000 aircraft were engaged in general aviation flying. This contrasts with approximately 2,200 commercial airliners in domestic use. Moreover, these 82,000 airplanes flew an estimated 13.3 million hours that year, over three times the number of hours flown by the commercial airlines.
After World War II many people thought the air- plane would become as commonplace as the auto- mobile, with millions owning and operating small, personal aircraft. Flight training was stimulated by federal government educational benefits granted to veterans. Enrollment in flight schools soared. In 1947, general aviation reached its all-time high in number of hours flown. This 1947 record of 16.3 million hours quickly dropped to an average level of 8.9 million hours during the period 1950-1955. (Figure 5.) Lim- ited utility and high operating and ownership costs of aircraft proved detrimental to the widespread growth of private flying.
Since 1946, however, an important trend has materi- alized. Businessmen have discovered that the airplane is a valuable tool in the operation of their enterprises. The total hours flown for business purposes increased from 2.6 million hours in 1949 to 5.5 million hours in 1962. In eleven years, the increase was two-fold and accounted for over 40 per cent of the total num- ber of hours flown in general aviation in 1962.
The use of business aircraft permits a company to expand its sales volume by increasing its market cov- erage without necessarily increasing the number of salesmen on its staff. For example, a 200-mph com- pany plane can fly from Dallas to Houston in one hour and 12 minutes; from New York to Boston in 55 min- utes; from Los Angeles to San Francisco in one hour and 42 minutes. The advantages of covering a regional sales territory by aircraft instead of by automobile are obvious.
General aviation aircraft also have many uses in addition to that of transportation. Farmers, ranchers, and others engaged in agriculture have found the air- plane valuable for aerial application of chemicals or seed to land, crops, and forests. Control of insect inva- sion is a most important aspect of this work.
Chartered passenger and cargo transportation is a significant part of general aviation. Commercial flying accounts for about 18 per cent of the total number of hours flown in general aviation activities. Included in this category are pipeline control, forestry patrol, mapping, aerial photography, mineral prospecting, and advertising, as well as agricultural flying.
Instructional flying, including dual and solo flight, is responsible for about 15 per cent of general aviation flying. Immediately following World War 11 instruc- tional flying accounted for over 60 per cent of general aviation activity. As veterans' benefits diminshed, in- struction also diminished, so that it soon represented the smallest portion of general aviation annual flying hours. Since 1955, this trend has reversed sharply, with instructional flying increasing from 1.3 million hours in 1955 to 1.9 million hours in 1962— an increase of 49 per cent. With the ever-increasing popularity of the airplane in business flying, the present increase in flight training promises to continue.
Personal flying tends to remain a fairly constant percentage (approximately 27 per cent) of the total hours flown in general aviation. The level of consumer income is a determining factor in the number of hours of pleasure flying.
It is estimated that the current value of the general aviation fleet exceeds $700 million. Add to this a $500 million per year sales volume of fixed-base operators serving over 200,000 active pilots, and it is evident that general aviation now has a firm foundation in the economy. In view of the great potential for increased business flying, this segment of aviation is expected to experience remarkable growth during the next decade.
The Social Aspect
In order to judge comprehensively aviation's effect on the "social man," it is necessary to review certain
LIVING IN THE AEROSPACE AGE
aspects of everyday life and determine how the air- mathematics of missiles and rockets, astronomy, ceies- plane has contributed to a re-appraisal, if not a re- tial navigation and geography, and flight engineering evaluation, of social concepts. development.
POPULATION DISTRIBUTION
Any important means of transportation moves popu- lations. Ships brought people to America; the railroads stimulated the growth of cities; the automobile dis- persed city people outward and drew rural inhabitants in toward the outskirts of the cities.
Aviation has a similar significance in the distribution of population. The out-of-the-way locality, where min- erals, chemicals, and other natural resources may be exploited, can be brought into contact with other population centers by the speed of air transportation. Similarly, the sparsely populated regions lying adja- cent to or on air routes, between densely populated centers, will tend to increase in population.
A closely related factor to future population distri- bution is the ability of the airplane to promote new business and trade activities in areas not now served by railroads or highways, but which, though undevel- oped, are potentially rich in resources. The 49th state, Alaska, is an excellent example of a potential popula- tion growth area.
EDUCATION
In an over-all sense, the influence of aviation on education is synonymous with its influence upon civi- lization and culture. Speaking of education in a narrower sense, i.e., a formal classroom-laboratory, teaching-learning process, aviation has had a tremen- dous impact on elementaiy, secondary, and university instruction.
Recently, a survey was completed which indicated that 47 institutions of higher learning conferred de- grees in aeronautical engineering on the basis of a four-year curriculum; 22 others conferred such degrees on the basis of a five-year curriculum; while 25 schools offered a program of studies in either aeronautical administration or other aviation service fields.
Aviation trade schools have been established in every state. There are 69 airframe and aircraft power- plant mechanics schools. Of the 843 flight schools, 216 teach flight and related subjects, and the other 627 teach flight only. In addition, many airlines, air- craft assembly factories, and aircraft engine plants maintain schools or apprentice training programs.
The social sciences not only tell the history of pow- ered flight, but also relate its social, economic, and political effects. The physical sciences include the theory of the airfoil, the physics of airframe con- struction, the chemistry of fuel and metals, the
FAMILY LIFE
The habits and living conditions of the family have also been affected by the introduction of the airplane. The most noticeable change has occurred in the family's choice of vacation sites. Within the usual two-week vacation period, it is now possible to visit scenic and historic locations which are thousands of miles away. Relatives who have moved to distant places are only hours away. Because of this, there has been a tendency for family members to feel a greater freedom of choice in choosing to relocate without necessarily weakening family ties.
Eating habits have been changed by the increased use of aircargo facilities. Foods from distant areas are now more readily available. New products are quickly distributed to the consumer and new markets created and expanded.
Widespread influence of privately-owned aircraft on family hfe is contingent upon the further devel- opment of low-cost, high-efiiciency, light airplanes. Privately-owned aircraft will provide a higher de- gree of personal mobility and influence sports activ- ities—specifically camping, hunting, and fishing— of families in higher income brackets. Big spectacle sporting events can be more easily attended, and increased sporting activity in more widely separated areas is possible.
The Political Aspect
Just as aviation has a social and economic impact upon persons and nations so, too, it has an effect in the realm of politics. In the fields of total air power, military strength, and international relations, the im- pact of aviation is noticeable.
MILITARY OPERATIONS
World War I indicated to military strategists that fundamental changes would be required in planning offensive-defensive actions in all wars. At first planes were employed only as mobile observation posts which could quickly and accurately report concentrations of enemy troops and fire power. As this activity in- creased, the next logical step to occur was an attempt to deny this activity to the opposition. Airplanes not only carried a pilot or a pilot and observer, but also a rifle and hand grenades. Soon, machine guns were mounted on the nose of the plane, and later bombs were also carried. During World War I, a new aviation jargon came into being and new tactics were evolved.
8 FUNDAMENTALS OF AVIATION AND SPACE TECHNOLOGY
but the full potential of aerial warfare was neither understood nor employed.
In the period between the two great wars, some nations did more to incorporate aviation into their military forces than did others. There was, however, a general lack of comprehension of the support, recon- naissance, fighter, bombing, and transport abilities of a modern air force. Although the first powered flight occurred in the United States in 1903, this country was one of the last major powers to become fully aware of the significance of the airplane.
The most famous of the early advocates of aviation, particularly in the military field, was General "Billy" Mitchell. He proved the superiority of the airplane over the battleship, but his strategical victory ended in his personal defeat. He was court-martialed and resigned from the Army, although he continued his fight for the recognition of a strong military air fleet. Today, the United States has implemented many of the ideas which General Mitchell attempted to pro- mulgate in the 1920's.
During World War O, the aviation industry "grew up," commercial air transportation was vastly ex- panded, and military commanders not only recognized the value of an air force, but assigned to it an equal area of responsibility with the Army and Navy. The importance of this partnership role of the Air Force was confirmed when the Congress decreed in 1947 that a new Cabinet-level post should be created, i.e., the Department of Defense, in which the Army, Navy, and Air Force had equal status.
Since World War II, the greatest demonstration of the use to which air power could be put was given
Figure 6 — A North Pole-Centered mop, or a polar projection, the new world geographic relationships created by the airplane
during the "Berlin Airlift." Thousands of tons of food, clothing, coal, and other necessities of life were air- lifted into beleaguered Berlin. This accomplishment was carried out without the loss of a life or the loss of an aircraft and was completed during all kinds of weather and on a 24-hour schedule.
Air power today includes the military air force, commercial air transportation, the aircraft indus- try, and general aviation. It is not the size of the fleet of military aircraft alone which detennines air supremacy.
INTERNATIONAL AFFAIRS
Until the beginning of World War II, it had been the American tradition to be isolationist— to "go it alone"— to avoid being involved in "foreign entangle- ments." Only a terrifying event, such as the bombing of Pearl Harbor, could change the thinking of the public for any length of time. There was, of course, a more liberal trend of thought— one which reflected a strong tie with Europe. This feeling of internation- alism was, for the most part, concentrated on the Atlantic Coast. This was logical, of course, because New York was closer to London, Paris, Rome, and Berlin than was Chicago.
It has only been since the end of World War II that many midwesterners and westerners discovered that they had been looking at the wrong map. The well-known Mercator Map did not give an accurate picture. The Polar Map clearly pointed out that the distances from Europe to Chicago, Denver, and Seattle were approximately the same as the distance from New York to these same places in Europe. ( Fig- ure 6.)
Commercial airlines, in 1957, began flying the Polar route over the top of the world, and doing it on sched- ule and at a high rate of speed. If the commercial planes could pioneer these routes and accept them as safe flying areas, speedy enemy bombers could do the same. Our military defense conception had to be revised when this most disturbing fact was finally acknowledged. The heart of the United States, in a third world war, could easily become a battleground. The long-distance, two-ocean defense system became obsolete. The airplane forced tlie American public to re-appraise and re-evaluate America's vulnerability and its traditional concepts concerning international relations.
In today's Aerospace Age, international affairs have become a dynamic force. Diplomacy and international relations are intelligently discussed by the average citizen. Although much of the credit can be given to the progress and enlargement of the communications system of the world, a part of this awareness of world
LIVING IN THE AEROSPACE AGE
events can be attributed to the rapid advances in commercial and private flying. It is no longer consid- ered unusual when a high official of government or industry travels to another country or continent for a conference and is back at his desk in a day or so. Where it formerly took days or even weeks for com- plete films of a great event in Europe to arrive and be distributed throughout the nation, today, by com- bining the airplane and the television set, the Ameri- can public can see a coronation or an historical event in less than ten hours after the event takes place. Or, again through the medium of television, they may view the actual firing of a missile from Cape Canav- eral, which, in itself, is a tribute to the importance of air power and already has influenced international affairs.
POLITICS
Another indication of aviation's importance may be noted in the use of airplanes by government officials, chiefly the President of the United States. The Office of the President has on call a small fleet which, in addition to jet aircraft, also contains helicopters.
It is notable that political campaigning methods have also changed during the past twenty years. It is no longer necessary for a candidate to spend much time away from his headquarters or to plan a cross- country trip where his speeches have to be given in geographic pro.ximity. In future campaigns, a can- didate may appear before an audience in Chicago on one day, in Dallas the next, in New York on the following day, and then in Los Angeles the day after that. Political leaders have become mobile and this factor has permitted and encouraged greater appreci- ation and understanding of American politics by a larger number of voters.
Summary
Today aviation exerts considerable influence upon the economic activities of mankind. The aerospace in- dustry provides thousands of job opportimities. It has grown to be a dominant employer in manufacturing. Further, this industry consumes a sizeable portion of the total defense budget, which is sustained by all taxpayers in this country.
Questions
Commercial aviation is entering a new era, with ever-widening horizons. The commercial jet airliner promises to revolutionize the travel habits of business- men and families alike. The distances of global travel have been reduced to a few hours of pleasant riding in air-conditioned, living-room comfort.
General aviation is coming into its own with the growing use of aircraft for business travel. Increasing acceptance of the airplane as an economic business asset will acquaint new thousands with private air travel. As consumer incomes increase, light aircraft ownership costs will fall within the reach of hundreds more. Freedom of movement, now associated with the automobile, may be shifted to the airplane.
Sociological change has followed the development of the airplane. The airplane has increased the living tempo, opened new markets, and affected the distri- bution of the world's population. Distant and previ- ously inaccessible areas will be opened, new towns will be constructed, and sparsely populated regions lying adjacent to air routes will increase in population.
Formal education will be vitally affected by avia- tion with all phases of the present educational system directly influenced by aviation activity. Family life has also been changed, principally in its choice of vacation sites and in the dispersion of family members to different geographical areas. Some variation has been noted in eating habits since speedy transporta- tion makes perishable products more easily available.
Politically, the airplane has changed military con- cepts. Today the United States Air Force has equal status with the Army and Navy. In international af- fairs, the airplane has forced the American public to re-evaluate its role in diplomatic relations. Now that the Polar route is being flown daily, the midwestern and west coast cities are as close to the capitals of Europe and Asia as are the cities on the east coast. Domestic political campaigns have been re-appraised in order to take advantage of airplane mobility. Politi- cal leaders can now cover more territory and speak to more citizens during a campaign than has ever before been possible.
Aviation in all of its varied facets represents a dy- namic force in a growing world. The changes it has brought and will continue to bring represent a never- ending challenge to the youth of today.
1. How has aviation aided in the redistribution of the world's population?
2. What are the three factors used to indicate the economic value of air transportation?
3. The helicopter is useful for many tasks. To what use is it particularly well suited?
4. What did World War I indicate to military strate- gists with respect to military aviation?
10 FUNDAMENTALS OF AVIATION AND SPACE TECHNOLOGY
5. Who was "Billy" Mitchell and what has been his contribution to the Aerospace Age?
6. List the tv'pes of jobs required to operate an air- line.
7. When was the Air Force officially created as a separate service?
8. In what way has American family life been af- fected by the airplane?
9. What are the five classifications into which the aerospace industry is generally divided?
10. State why it is important for modern youth to understand the nature and various aspects of aerospace activities.
11. What does the definition of air power include?
12. About what per cent of the people in the United
States have flown in an airplane?
13. Relate the various ways in which aerospace in the United States directly influences the economic activities of individuals.
14. What is the most important segment of general aviation? Discuss the reasons for its growing importance.
15. Compare the performance capability of a new commercial jet airliner with that of a convention- ally-powered commercial airliner.
16. What is the economic significance of the growth in aerospace manufacturing since 1947?
17. Why has the ability to navigate the Polar route safely caused a change in United States military defense planning?
Chapter 2 History of Flight
Since the beginning of recorded history, there have been evidences in the drawings and folklore of all peoples that man has always wanted to fly— that he longed for wings. Even the earliest of prehistoric men, to whom the invention of the stone ax was a develop- ment of great importance, must have gazed upward and, like his descendants for thousands of years, en- vied the freedom of birds and their ability to sail gracefully far up into the sky.
The first expressions of man's desire to fly, and his first realizations of his utter inability and helplessness, are to be found in early legends and mythologies. Man, being unable to soar up into the heavens, endowed his gods with the ability to fly.
Everyone is familiar with the Greek messenger god, Hermes, and his winged sandals; the German Val- kyrie who descended from the abode of the gods to battlefields on earth and carried back with them to Valhalla the slain heroes; the legend of Bellerophon; the wonderful winged horse Pegasus; and countless other stories.
The first concrete evidence of man's attempt to con- struct a flying machine occurred about 400 B.C. Archytas, a Greek philosopher and disciple of Pythag- oras, became interested in flying and allegedly con- structed a wooden pigeon. According to scanty rec- ords now available, the bird flew, but details of its construction and source of power were not recorded.
Undoubtedly there were other attempts to fly by men in later centuries, but the first man to work out plans intelligently for flying devices was the master artist Leonardo da Vinci. About the time of Christo- pher Columbus, da Vinci developed a toy helicopter by constructing small pinwheels out of paper. He also spent considerable time in designing flying machines patterned after bodies of birds. These machines had flapping wings which moved when the flyer pumped his arms and legs up and down. Although he built machines from his plans, needless to say da Vinci's physical strength could not develop sufficient power to raise himself from the ground. Had there existed
at that time a practical engine, an airplane would probably have been flown successfully centuries be- fore the Wright brothers made their flight.
Other drawings executed by da Vinci included the plan for the first propeller and the first parachute. As a result of his careful observations of birds, he became the first proponent of modern streamlining.
Balloons and Gliders
In many countries and for many years men contin- ued their search for the secrets of flying. These early experimenters studied the physical stnictiu-e of birds' wings and from this research attempted to construct man-carrying wings. These efforts to develop omi- thopters were singularly unsuccessful.
Sir George Cayley (1773-1857), a distinguished British scientist, scoffed at the flapping-wing idea. It was his belief that a machine with a fi.xed wing or wings was the solution to flight and that the machine should have mechanical power to drive it through the air.
During the latter part of the 17th century and the early years of the 18th century it was in France that the greatest amount of research and experimentation was done. In 1678, Besnier built a pair of wooden wings covered with fabric. With these hand-made con- trivances, he glided successfully, at first from low hills, and finally from the highest window in his house to the ground below. To him goes the honor of being the first successful glider pilot.
Handicapped as the early pioneers were by lack of power and suitable materials for their experiments, it is not surprising that man first left the earth in a balloon, not in an airplane. The discovery in 1766 of a very light gas called hydrogen, and the observation, by two French paper mill owners, the Montgolfier Brothers, that warmed air rises, was responsible for the early experiments in 1783.
Following the wave of enthusiasm and interest which developed after the successful balloon flight
12 FUNDAMENTALS OF AVIATION AND SPACE TECHNOLOGY
of the Montgolfiers, many men conducted other bal- loon flights. The major problem these men attempted to solve was that of finding a method to control the direction of a balloon flight.
The first flight by a dirigible balloon or airship is attributed to Henri Giffard. He constructed a light- weight steam engine of about 3 hp and fitted it to his airship, which had an envelope with pointed ends, thus establishing the cigar shape which was to be characteristic of airships throughout their period of development. On September 24, 1852, this airship made a flight of 17 miles, starting from the Hippo- drome in Paris and landing near Trappes.
France continued to lead in the development of the airship for another hundred years, though inventors in Italy, Great Britain, and Germany were making some contributions to its development. One of the most colorful personalities among the experimenters was Santos-Dumont, a Brazilian living in France. Be- tween 1897 and 1904 he built and flew 14 airships.
During this period the first known rigid airship was built by an Austrian, David Schwartz, in Berlin. It made a flight but did not live up to expectations. The work of Schwartz was probably most important be- cause it influenced Gount Ferdinand von Zeppelin, a retired German army officer, to begin work on dirigible airships.
Zeppelin was a fine engineer and his work with dirigibles was so outstanding that airships are often called Zeppelins. The first airship built by Zeppelin was launched on July 2, 1900, at Lake Constance, Ger- many. It had a capacity of about 350,000 cubic feet of hydrogen, a cigar-shaped aluminum girder frame, and was propelled by two benzine engines each driv- ing two four-bladed propellers. The outer cover was of linen. It was called the LZ-1 and was nearly 420 feet in length and 38 feet in diameter. This first rigid airship made three successful flights but its further development was abandoned thereafter because of lack of money.
Of all the early pioneers, the man whose work was most helpful to the Wright Brothers was Sir George Gayley. As a lad, Cayley was in the crowd that wit- nessed the balloon flights of de Rozier, who was the first man to fly in the Montgolfier balloon. Cayley first experimented with paper helicopters, flapping- wing gliders, and finally a rigid, fixed-wing glider. He at first flew the glider by running downhill with it suspended over his head. Later, he discovered that, with modifications, the wing had sufficient lifting power to sustain his weight. Continued experiments led him to adopt a double-wing glider or biplane. He also tried to design and construct a light engine which would permit his glider biplane to take off
under its own power. However, due to the lack of materials which were both light and strong, he failed. Nevertheless, he had made a lasting contribution to the science of aeronautics.
Generally speaking, the era of haphazard experi- mentation was over by the middle of the 19th century. Through careful research, the outstanding pioneers who followed Cayley developed more effective wing shapes, methods of balance and control, and, ex- tremely important, they made thousands of test flights. These men include the Frenchman Octave Ghanute, the German Otto Lilienthal, Professor John J. Mont- gomery (the first American to achieve success), and Professor Samuel P. Langley.
Professor Langley, a scientist associated with the Smithsonian Institution, designed and built a few suc- cessful models but was destined never to achieve the distinction of being the first man to pilot an airplane. His designs were exceptionally good. Professor Lang- ley's largest and last airplane crashed after taking off from a houseboat on the Potomac River shortly before the flight at Kitty Hawk. It is interesting to note that quite a few years later a machine was constructed following his original design and, with only a few minor modifications, was successfully flown by Glenn H. Curtiss.
Experiments of the Wright Brothers
The Wright brothers operated a small bicycle shop in Dayton, Ohio. Like most American boys, they had built and flown many kites. Their interest in airplanes, however, became seriously aroused after reading of the experiments and flights of Octave Ghanute and Otto Lilienthal and the experiments of Professor Langley.
They collected as much data as was then available and began their experiments by copying the various types of wings that had been developed and by test- ing those wings under a wide variety of conditions. They found that both Langley and Lilienthal had been correct in many of their theories, but, by further ex- perimentation, they were successful in discovering new facts concerning the airplane wing. They also de- veloped a small wind tunnel in which they tested hun- dreds of variously-shaped wings and made careful note of the performance characteristics in each case.
Their scientific approach to the problem of flight was destined to bring them success. On the basis of their experimentations Wilbur and Orville Wright designed and built a glider, which, when tested at Kitty Hawk in 1902, was by far the most satisfactory glider yet built. They made over one thousand flights, some of which ranged between five hundred and a
HISTORY OF FLIGHT 13
thousand feet— an unheard of distance at that time.
During this period the Wrights also designed, under necessity, a satisfactory rudder— the forerunner of our modern aileron, a control which banks the airplane to the left or right. To accomplish this the pilot actu- ally bent or warped the trailing edge of each wing as necessary, thus enabling the glider to fly "straight and level." The basic method of moving the controls, developed by the Wrights in 1902, is practically the same as that in use today.
After bringing the glider to a high state of perfec- tion, the Wrights next turned their attention to power. After searching widely among all types of gasoline and steam engines, they reluctantly came to the con- clusion that no suitable engine existed. All of the types studied were either too heavy or lacked sufficient power. It was typical of these men that, faced with such a difficulty, they did not give up their dreams but sat down and painstakingly designed and built a light yet fairly powerful engine.
Still another handicap awaited them. No one could give them any valuable information on propellers. Although steamboats had been using water propellers for quite a long time, little work and practically no thought had been expended on propeller design. Thus they were further delayed by the necessity of design- ing, testing, and constructing many models of pro- pellers, emerging in the summer of 1903 with two suc- cessful designs. Finally, all was in readiness.
Man's First Flight
On a cold, blustery morning, the 17th of December, 1903, man's dream for centuries was realized. Just after half past ten, Orville Wright took the pilot's position, a prone arrangement developed during their glider experiments. Wilbur stood at the wing tip to steady the machine as it moved along the rail. The engine was warmed up for two or three minutes, and then the aircraft moved along a launching rail and took off, to remain in the air for 12 seconds, when it
Figure 7 — The Wright Biplane in Flight oyer the Sands of Kitty Hawk.
darted to the ground. Its forward speed was 7 mph. There were only five people to witness this event, but fortunately the first flight was recorded by one photo- graph, which has been reproduced hundreds of thou- sands of times and seen by millions of people since that day. (Figure 7.)
Later Developments
After the initial success of the Wright brothers, improvements in airplane and engine design came swiftly. Longer flights at greater speeds and higher altitudes succeeded each other with amazing rapidity. Louis Bleriot, a Frenchman, crossed the English Chan- nel in 1909. C. K. Hamilton flew from New York to Philadelphia and back again in 1910. It was not until World War I, however, that large-scale development and construction of the airplane took place. For the first time, governments of the world spent consider- able money and time to improve airplanes for recon- naissance, fighter, and bomber puqjoses.
At the end of the war, private flying expanded. Gov- ernment surplus planes were sold to former military pilots. These aircraft, soon appearing wherever there were open grassy fields, introduced the miracle of flying to thousands of people. The search for improved design and construction of engines and airframes con- tinued. Better materials and safer methods of construc- tion were discovered. More powerful engines were built to assist man in his efforts to conquer space.
In 1919, the Atlantic Ocean was spanned by United States Navy airmen in a Curtiss flying boat, the NC-4. In 1922, General "Billy" Mitchell flew a Curtiss "Racer" at 222.9 mph to hold the world's speed record. Mem- bers of the United States Army Air Service flew around the World in 1924. In 1926, Commander Rich- ard E. Byrd and Floyd Bennett flew over the North Pole. Charles Lindbergh and The Spirit of St. Louis made the first non-stop flight from New York to Paris in 1927. Byrd and Balchen flew over the South Pole in 1929. Speed over distances occupied the attention of Frank Hawks, Roscoe Turner, Kingsford-Smith and others. Women pilots, among them Ruth Nichols, Amelia Earhart, and Jacqueline Cochran, also helped to set some of the early records.
Round-the-world flying became a popular test. In 1931, Wiley Post, with Harold Gatty as navigator, made such a flight in a single-engine Lockheed— T/ie Winnie Mae— in a little more than eight days. In 1933, Post did it alone in seven days. This record stood until 1938 when Howard Hughes and a crew of four in a twin-engine Lockheed flew the 14,791 miles in some- what less than four days. In February, 1949, Captain James Gallagher and the crew of a United States
14 FUNDAMENTALS OF AVIATION AND SPACE TECHNOIOGY
Air Force B-50-Thb Lucky Lady //-flew non-stop around the world in 94 hours and one minute. In April 1964, Mrs. Jerrie Mock, a Columbus, Ohio, housewife became the first woman to complete successfully a solo round-the-world flight.
Year by year, world speed records were steadily improved: Al Williams-266 mph in 1923; Adjutant Bonnet of France-278 mph in 1924; James Doolittle— 294 mph in 1932; James R. Wendell-304 mph in 1933; Raymond Delmotte of France— 314 mph in 1934; Howard Hughes— 352 mph in 1935; and then the Germans forged ahead with Herman Wunster flying 379 mph in 1937 and Fritz Wendell-469 mph in 1939.
These surprising increases in speed set the stage for a new type of aircraft, the jet-powered airplane. On August 27, 1939, a German Air Force captain flew a Heinkel 178 with a turbojet engine. This German achievement was quickly followed by a successful British jet-powered aircraft in May 1941. But the honor of being the first man to break the sound barrier goes to an American flying an American-designed and manufactured airplane. On October 14, 1947, Capt. Charles (Chuck) Yaeger, in a Bell X-1, flew at a speed of Mach 1.45 (968 mph); on December 12, 1953, he flew at two and a half times the speed of sound. In e.xactly 50 years to the month, man had developed and refined aircraft construction and engine design to such a degree that speed had progressed from 7 mph to 1,650 mph.
Recently new world records in several categories were established. In 1961, A. Fedetov, a Russian, flew a P-166 jet 1,491.9 mph over a closed-circuit course.
Then in 1962, Maj. Clyde Evely and his USAF crew flew 12,532.28 miles in a B-52H, a non-stop "distance in a straight line", from Okinawa to Madrid. Maj. Robert M. White set an altitude record of 314,750 ft. in the X-15-1, and the Russian Gueorgui Mossolov flew an E-166 jet at 1,665.89 mph over a "straight course".
Air-Mail and Air-Passenger Transportation
Air transportation as a commercial enterprise had its beginning in the carrying of the air mail. Air-mail service began in the United States as an experiment, in September, 1911, when a temporary post office was set up on the outskirts of Mineola, New York. During the period of a week, mail was flown from the edge of this Long Island town to the post office in the town.
There were further small-scale experiments, and in 1912 the Post Office Department asked Congress for the modest sum of $50,000 with which to initiate a regular air-mail service. It was not until 1916, how- ever, that Congress finally made some funds available. The Post Office Department advertised for bids for air-mail service, but no one submitted an offer since
there were no airplanes of suitable construction for the purpose.
In 1918, Congress appropriated $100,000 for the establishment of an experimental air-mail route, and in May of that year the first official air mail route linked the cities of New York and Washington. By 1921 the first transcontinental air-mail route was formed, with the first flight, a dramatic milestone in air transportation history, being made in 33 hours and 21 minutes.
After air-mail service had been operated by the Post Office for several years. Congress, in 1925, passed the Air Mail Act (Kelly Act) which made provision for the carrying of air mail by private contractors. The Kelly Act provided the impetus which aroused private industry and capital to the opportunities in the field of air transportation. By 1927, private contractors had accepted responsibility for all air-mail routes, rapidly expanding this service to many new cities while planning for the coming era of passenger service.
The last air-mail route to be turned over to private contractors was the transcontinental route. William E. Boeing, an airplane builder, submitted the low bid and within five months had put into operation 25 new and specially constructed mail planes. This particular air-mail operation formed the nucleus of what was later to become United Air Lines.
Because of the pioneering done by air-mail pilots, the enactment of the Kelly Act and the Air Commerce Act of 1926, and the surge of interest by industry in the development of better planes, more powerful en- gines, and increasingly useful navigational aids, air- passenger and freight transportation have been able to assume an important role in American life.
Summary
Since the beginning of recorded history there have been evidences of man's desire to fly. When early man realized his inability and helplessness to soar through the air, he assigned the ability to fly only to his gods.
Archytas's wooden pigeon, about 400 B. C. was the first concrete evidence of man's attempt to construct a flying machine. Leonardo da Vinci, however, was the first to work out plans intelligently for flying devices, including ideas for a propeller and a parachute.
The first glider pilot was a Frenchman, Besnier. He glided successfully in 1678. Man first left the ground for extended periods in balloons. The Montgolfier brothers accomplished this feat in 1783. During the following 125 years balloons, airships, and zeppelins were constantly improved.
Sir George Cayley, an Englishman, Octave Chanute, a Frenchman, Otto Lilienthal, a German, and Profes- sors John J. Montgomery and Samuel P. Langley,
HISTORY OF FLIGHT 15
Americans, greatly influenced the experiments of the Wright brothers.
After experimentation with gliders and the devel- opment of a suitable engine, a satisfactory rudder, and a workable propeller, the Wright brothers achieved lasting fame by being the first men to fly a heavier- than-air craft at Kitty Hawk, N. C, on December 17, 1903.
In rapid succession, the Atlantic and Pacific Oceans were spanned. New speed and altitude records were
constantly being set. Round-the-world flights became commonplace.
Engine and airframe design continued to improve. The first turbojet airplane was built and flown in 1939. Supersonic flight followed soon thereafter.
In the 1920's, the United States Post Office Depart- ment encouraged and subsidized the first air-mail routes. These routes, with the pilots and planes con- cerned, provided the nucleus for the development of the modem-day airlines.
Questions
1. What was the Kelly Act and why was it impor- tant?
2. When and where was the first jet airplane suc- cessfully flown?
3. What was the role of Count Zeppelin in the development of the airship?
4. Trace the development of air-mail service from 1911 to 1927.
5. Of what significance in aviation history are the dates 1909, 1919, 1927, and December 12, 1953?
6. What was the importance of da Vinci's research and planning?
In what type of device did man first leave the ground?
What were the limitations of the free balloon? In what way did the Wright brothers use gliders? Name the contributions of Sir George Cayley to gliding flight.
Who developed the rudder and how does it control the airplane? 12. What formed the basis for our present widespread commercial air transportation?
11.
Chapter 3 Theory of Flight
Whenever, in casual conversation, a group of peo- ple start to discuss airplanes, someone is almost cer- tain to exclaim, "Why, some of those airplanes weigh tons. I don't see how they stay in the air." Very few people understand the forces that control an airplane in flight.
For many years engineers have studied the motion of air over airplane parts in order to learn how a change in the shape of the part affects the force created on it by the moving air. Although a large amount of information is presently available on this subject, the desire to make airplanes go higher, faster, farther, and carry greater loads requires continuous research.
A balloon rises in the air because its bag, which is filled with a gas lighter than the air at low altitude, displaces the heavier low altitude air. The difference between the weight of the heavy air displaced and the light air inside the bag equals force, and force is the element which lifts the balloon. Air gets lighter as altitude increases; consequently, at an altitude where this weight difference between the air in the bag and the displaced air is equalized, the balloon stops rising and remains at that altitude. Balloons are referred to as lighter-than-air craft.
Figure 8 — An exaggerated view of air movement around a wing moving through the air at a relatively high speed. The pressure on the upper wing surface is less than on the lower causing a force, called lift, to be directed upward.
The airplane does not get its lift in the same man- ner as the balloon; in an airplane, lift depends upon the relative motion between wing and air. Airplanes, therefore, are referred to as heavier-than-air craft.
To understand how very large loads are carried by airplanes, one should realize that each square foot of wing area can lift a certain weight at a certain speed. By increasing the wing area— lift— larger loads can be raised. The lift developed by a specific wing will depend upon its shape and size, the speed at which it moves through the air, and the angle at which it strikes the air.
Shape of the Wing
Imagine that a wing is cut along a line drawn be- tween its front edge ( leading edge ) and its rear edge (trailing edge). This cross-section will expose a por- tion of the wing that shows the shape of the airfoil. This airfoil will be rounded at the leading edge and sharp at the trailing edge in those airplanes which are not designed to fly at supersonic speeds. The upper surface of the airfoil is curved and the lower surface is almost flat. The thickest part of the airfoil lies approximately one-third to one-half the distance between the leading edge and the trailing edge. (Fig- ure 8.)
When looking down at the airplane, one sees the span. The span is the distance from one wing tip to the other. The chord is the distance between the lead- ing and trailing edges. The span is usually between five and ten times as long as the chord. A wing with a large span in comparison to the chord has less resist- ance to motion through the air (drag) than does a wing with a small span in comparison to the chord.
Speed of the Wing
If we move the wing through the air at a relatively high speed with the rounded or leading edge forward, the following things happen: The blunt and thick
THEORY OF FLIGHT 17
leading edge pushes the air out of the way. Part of this displaced air flows rapidly (the speed is impor- tant) over the wing and part of it flows under the wing. The layers of air, after going over and under the wing, join again behind the trailing edge. The important thing to remember is that due to the curved upper surface the air that flowed over the wing had to go farther than the air that went under the wing. Consequently, air that flowed over the wing had to travel faster than the air that went under the more or less flat bottom surface.
The air which had to travel farther across the top of the wing is stretched out and becomes thinner, creating a reduced pressure on the upper surface. The air traveling along the bottom of the airfoil is slightly compressed, and consequently develops in- creased pressure. The difference in pressure between the air on the upper and lower surfaces of the wing, when exerted on the entire wing area, produces lift. (Figure 8.)
The faster the wing is moved through the air the greater the pressure difference will be, with a result- ing increase in total lifting force. The heavier an air- plane is in relation to its total wing area, the higher the speed must be to develop enough lift to get it off the ground and sustain flight.
Lift and Angle of Attack
There is another element that affects the amount of lift produced by a wing, i.e., the angle at which the wing strikes the air. If the wing is held flat and moved straight ahead, some Ifft is generated. More lift is obtained, however, if the leading edge of the wing is elevated slightly above the trailing edge, i.e., if the wing goes through the air at a higher angle of attack.
At a higher angle of attack the wing displaces more air; that is, it makes the air over the wing travel far- ther, and, up to a certain point, develops more lift. However, every wing has a stalling angle of attack at which lift drops off abruptly. This sudden loss of lift (stall) is caused by the swirling and burbling of the air over the top surface of the wing (Figure 9) and occurs when the angle of attack is so great that it exceeds the angle necessary for maximum lift. When an airplane stalls, the nose drops, the speed increases, and the angle of attack decreases. If, however, both the nose and one wing drop, the airplane will rotate hke a leaf falling from a tree. This flight attitude is called a tail spin, and, although the nose is down and the airplane is diving, the new angle of attack exceeds the stalling angle. To compensate for this unusual diving attitude, the pilot must first lower the nose
still farther, reduce the angle of attack below the stalling value, stop the rotation, and then bring the airplane back to a straight and level flight attitude.
Lift and Weight
The amount of the lift, then, is determined by (1) the shape of the wing, (2) the speed of the air- plane, and (3) the angle of attack. The amount of Itft required depends on the weight of the airplane and whether it is flying level, climbing, or diving. ( Figure 10. ) To climb, the wing's lift must be greater than the airplane's weight; during descent the wing's lift is less than the airplane's weight.
Thrust and Drag
To produce lift, the airplane wing must move through the air at a relatively high speed. This high speed is produced by a force or thrust which is ex- erted in the direction of the airplane's motion. Both a propeller and a jet engine produce thrust.
The blades of a propeller are small wings. When they rotate they create forces in the same manner as the wing creates Ifft except that the forces on the propeller blades act in the direction of the airplane's motion and are called thrust. A jet engine bums a mixture of fuel and air and exhausts this mixture toward the rear of the airplane. A force exerted inside
Figure 9 — Lift increases as the angle of attack is increased, up to a certain point. Wtien the angle of attack becomes too greet, however, the air seporates from the upper surface, destroying the smooth flow, and reducing the lift.
18 FUNDAMENTALS OF AVIATION AND SPACE TECHNOLOGY
the jet engine and in an opposite direction to the movement of the gas is needed to exhaust this gas at a high speed. This force, also, is in the direction of the airplane's motion and is called thrust.
The amount of thrust required depends upon the airplane's drag, and upon whether it is climbing, div- ing, or flying straight and level. Drag is the resistance an airplane meets in moving through the air. The faster the airplane moves, the greater will be the drag. Moving air exerts a similar force against the body when one tries to stand in a high wind.
In level flight, if the airplane speed remains con- stant, thrust is equal to drag. (Figure 11.) To accel- erate the airplane, thrust must be greater than drag and additional thrust is produced by burning more fuel in the engine. If thrust is increased, the airplane speeds forward until drag again equals thrust, and the airplane once more flies at a constant speed. As the speed increases, lift also increases; consequently, it is necessary to reduce the wing's angle of attack by low-
Figure 10 — Lift must exactly equal the to maintain steady flight.
iight of an airplane in order
Figure 11 — When the airplane to the drag.
not accelerating, the thrust is equal
ering the airplane's nose so that lift will again equal the airplane's weight and the aircraft will remain in a straight-and-level flight attitude.
Thrust must also be increased if the airplane is to climb at approximately the same speed it maintained while it was in level flight. To get the additional lift, the angle of attack must be increased, but this flight attitude also increases the drag. Additional thrust, therefore, is needed to counteract the additional drag and lift the airplane to its new altitude. During take- off, maximum engine power is used to accelerate the airplane and cause it to climb rapidly. During descent, the weight of the airplane helps to overcome drag, thereby requiring less thrust to maintain a constant air speed.
Drag greatly affects the amount of thrust required for various flight attitudes. To obtain the desired air- plane performance with minimum engine weight and fuel consumption it is necessary to minimize thrust. Consequently, airplane designers have studied the shape of various airplane parts to discover which shapes offer the least resistance to the movement of air across their surfaces. Those which have been found to have the least drag and which permit the air to flow smoothly over their surfaces are called stream- lined shapes. They require the least thrust to move them through the air.
Inherent Stability
To fly properly, an airplane must be designed so that all the forces applied on it during flight will bal- ance. In other words, the airplane must be stable enough to fly straight and level with a minimum of physical control by the pilot, i.e., the pilot must be able to change the plane's direction or cause it to climb or dive easily.
If the reader has built model airplanes, he will have discovered that before they will fly they must be balanced and the distribution of weight equalized. An airplane that is tail-heavy, nose-heavy, or one- wing-heavy is badly balanced. The airplane's center of gravity is that point about which the airplane bal- ances. It should be near hut always just ahead of the center of lift. This is the first consideration for inher- ent stability, or "built-in stabilit)'."
If a sheet of paper is skimmed through the air, it will fly an erratic and unpredictable flight path rather than a straight line. If the sheet of paper is folded into a dart shape, it will do better, but it will still turn and roll erratically. It has only a minimum amount of inherent stability. A carefully built model airplane, however, flies straight and level unless it is blown off course bv air currents. The stabilizers built
THEORY OF FLIGHT 19
AXIS OF PITCH
AXIS OF YAW
AXIS OF ROLL Figure 12 — An airplane may be controlled about tlie three axes of pitch, yaw and roll
into a model airplane are the same, in principle, as those used on an airplane.
The vertical stabilizer is a fixed tail airfoil which stands upright. It prevents the airplane from yawing, i.e., swinging left or right. The horizontal stabilizer, like a small wing, is the horizontal part of the tail. It prevents the airplane from nosing up or down.
There is still another way in which an airplane can move. It can roll, wing down or up. Consequently, wings are constructed and positioned on an airplane so that they tend to keep the airplane stable in roll.
The Axes of Rotation
An airplane is free to turn in three planes, whereas an automobile turns in only one plane. Think of an airplane as having three axes of rotation, all passing through the center of gravity. The longitudinal axis, or axis of roll, extends lengthwise through the air- plane's fuselage; the lateral axis, or axis of pitch, goes lengthwise through the wings; and the vertical axis, or axis of yaw, is perpendicular to the other two, and perpendicular to the earth's surface when the airplane is in straight and level flight. (Figure 12.)
To illustrate these rotations cut a piece of card- board into a rough airplane shape, and follow this
explanation: Turn to the left or right around the vertical axis. That is called the axis of yaw and is the only axis about which you can turn an automobile.
Now put the nose down and the tail up, or the nose up and the tail down. That is called rotation about the axis of pitch, or lateral axis. By controlling that rota- tion you put an airplane in the proper position to climb or dive. Next roll the left wing down and the right wing up, or the other way around, and you have rotation about the axis of roll, or the longitudinal axis.
To control the flight path of the airplane around its three axes, movable control surfaces are used: the rudder, elevator, and ailerons.
Rudder
Movement about the axis of yaw is controlled by the rudder, and the rudder is controlled by foot pres- sure on the cockpit's rudder pedals. (Figure 13.) When pressure is applied to the right rudder pedal, the nose of the airplane swings to the right. When pressure is applied to the left rudder pedal, the nose of the airplane swings to the left. The nose swings because the action of the rudder pedal turns the hinged rudder away from the longitudinal axis, and as the air strikes the rudder it literally pushes the tail of the airplane to the opposite side.
20 FUNDAMENTALS OF AVIATION AND SPACE TECHNOLOGY
^ \l
1
f
Figure 13 — Pushing the left-rudder pedal moves the rudder to the left causing the airplane to rotate to the left about its vertical axis. Push- ing the right-rudder pedal mokes the airplane rotate to the right.
Elevators
Movement around the axis of pitch is controlled by the elevators, as shown in figure 14. The elevators respond to forward and backward pressure on the control stick or wheel. In normal flight when forward stick is applied, the nose of the airplane is lowered. This action is caused by the lowering of the elevators which, as the wind strikes the elevator surface, forces the tail up and the nose down. The reverse action occurs when the stick is moved backward.
Figure 14 — Forward movement of the stick lowers the elevators caus- ing the airplane to nose down with rotation about its lateral axis. Backward movement of the stick raises the elevotors causing the air- plane to nose up.
Ailerons
Movement around the axis of roll is controlled by the ailerons. The ailerons respond to sideways pres- sure applied to the control stick as shown in figure 15. Pressure applied to the stick toward the left depresses the left wing. Pressure on the stick toward the right depresses the right wing. The ailerons are linked to- gether by control cables so that when one aileron is down, the opposite aileron is always up. As in the case of the elevators and rudder, the wind strikes the obstructing surfaces, raising the wing whose aileron is down, lowering the wing whose aileron is up, thus turning the airplane around its longitudinal axis.
Coordination of Controls
Control pressures are not used separately. The sim- plest maneuver needs coordination of all three pres- sures. A simple turn to the left requires coordinated pressures on the rudder, elevator and ailerons.
Trim Tabs
Even though an airplane has inherent stability, it does not always tend to fly straight and level. Remem- ber that the weight distribution in an airplane affects its stability and that various speeds affect the air-
THEORY OF FLIGHT 21
Figure 15 — Movement of the stick to the pilot's left raises tlie left aileron and lowers the right aileron, causing the airplane to bank to the left. Similarly, right stick bonks the airplane to the right.
plane's flight characteristics. If the fuel from one wing tank is completely used before fuel is used from an- other tank, the airplane tends to roll toward the full tank. All these variations require a pilot to exert addi- tional pressure on the controls for correction.
WhUe climbing or gliding, it is necessary to exert pressure constantly to keep the airplane in the desired
attitude. This constant control pressure is tiring in a small airplane, exhausting in a medium-size airplane, and impossible for any length of time in a heavy airplane.
For this reason airplanes are constructed with trim tabs. Trim tabs are small, hinged, control surfaces attached to the main control surfaces, i.e., rudder, elevators, and ailerons. (Figure 16.) Trim tabs are controlled by rotating a crank or a wheel in the cockpit or by pushing a button which electrically moves the tabs. By using trim tabs the pilot can bal- ance the forces on the controls so that, with hands off the controls, the airplane will fly either straight and level or in a climbing or gliding attitude. Trim tabs actually operate like the control surfaces to which they are attached. That is, if the rudder tab (Fig- ure 17) is set toward the left, it pushes the rudder to the right, thus making the airplane yaw to the right.
FORCES RUDDER RIGHT
Figure 16^This drawing shows location of trim tabs which ore ad- justed by the pilot to produce straight and level flight, constant climb, glide, etc.
Figure 17 — Diagram Showing How the Airstream Acts on the Rudder Trim Tab to Push the Rudder to the Right
22 FUNDAMENTALS OF AVIATION AND SPACE TECHNOLOGY
Summary
Lift is the force which raises the airplane off the ground and sustains it in the air. The hfting surface, or wing, is shaped so that when it passes rapidly through the air it produces the greatest amount of lift in proportion to the smallest possible amount of drag.
The amount of lift can be varied by changing the angle at which the wing strikes the air. This angle is known as the angle of attack. If the angle of attack is too great, as in an extremely steep climb, the air will cease to flow smoothly over the top of the wing, lift will be destroyed, and the airplane will stall.
Lift acts in the opposite direction to the weight, i.e., when lift exceeds weight the airplane climbs and when lift is less than weight the airplane descends.
In order to propel the airplane through the air rap- idly enough to maintain lift, the airplane must have thrust. Thrust acts in a direction opposite to drag. Drag is the resistance the airplane encounters while moving through the air. In normal level Hight at con- stant airspeed, lift balances weight and thrust balances drag.
These four forces— lift, weight, thrust, and drag- must be controllable by the actions of the pilot so that the airplane can climb, glide, accelerate, decelerate,
etc. However, in order that these forces may be easily controlled, the airplane must be very carefully bal- anced. In other words, it must be stable.
Special airfoils are built into the airplane to achieve this stability. The horizontal stabilizer tends to keep the airplane from pitching, the vertical stabilizer as- sists in keeping the airplane from swinging to the left or right, while the wings are designed and placed on the airplane so that they tend to keep it from rolling.
So that the pilot may be able to force the air- plane to rotate around one or more of its axes, control surfaces are supplied. The rudder swings the nose of the ship left or right around the airplane axis of yaw (vertical axis), the elevator forces the tail of the air- plane up or down (lateral axis), while the ailerons bank the wings left or right around the axis of roll (longitudinal axis). Although in conventional air- planes these controls are separate and distinct, they must be coordinated in most maneuvers in order to produce the proper flight action.
Additional controls required in all large airliners, and desirable in small planes, are the trim tabs. These small control surfaces, located on the rudder, the ailerons, and the elevators, assist the pilot by deflect- ing the control surfaces just the right amount to keep the airplane at the desired attitude.
Questions
1. What is lift?
2. Describe how wing lift is affected by its:
a. Airfoil shape.
b. Speed through the air.
c. Angle of attack.
3. What is the general shape of an airfoil?
4. What happens to the air when a wing is moved through it at a relatively high speed?
5. How much lift is required?
6. What is thrust? Drag?
7. How much thrust is needed?
8. What are the relationships between thrust-drag and weight-lift in straight and level flight?
9. For what reasons is stability important?
10. What is inherent stability? What are the consid- erations for it?
IL What are the stabilizing surfaces and their func- tions?
12. What are the axes of rotation?
13. What controls the airplane around each axis?
14. What is a trim tab? Where are they placed? For what reason?
THEORY OF FLIGHT 23
Chapter 4 Aircraft
The airplane of today is far removed from the flimsy, kite-like, underpowered craft of 1903, and there is much evidence that this advancement wOl continue in the years to come. Following World War I the airplane became an intricate and complex product of skilled, precision workmanship, possessing quali- ties of high performance and dependability. The great role played by the airplane in World War II was a direct result of the continued refinement of the design techniques and the manufacturing skills that gave the airplane ever-increasing performance and utility.
Since the last great conflict, the airplane has been widely accepted by both civilian and military users. Due to this increased use, the aircraft and allied in- dustries now employ more persons than any other industry in the United States. Aircraft production has created many new jobs, and there is an ever-increasing need for new processes, new materials, and new skills.
Aircraft are divided into two general classes: heavier-than-air craft and lighter-than-air craft. The major emphasis today is on the airplane with its many
variations in design, type, size, construction, and power. It is the purpose of this chapter to describe the basic types of airplanes and their principal components.
General Structure of an Airplane
Structurally, the airplane is usually divided into five main sections, i.e., (1) wings, (2) fuselage (or hull, in the case of a flying boat), (3) tail assembly, (4) landing gear, and (5) powerplant (which includes the propeller, if there is one. ) ( Figure 18. )
A visit to any large airport will show that airplanes are either monoplanes, with one wing (figure 19), or biplanes, having two wings (figure 20). Early at- tempts to build airplanes with still more wings proved to be unsatisfactory. The monoplane is now consid- ered more efficient than the biplane and consequently is in widespread use for commercial, military, and private flying. Biplanes today are used principally for crop spraying and instructional purposes.
Figure 19 — Monoplane
Figure 20 — Conventional Biplane Showing Upper and lower Wings and Wing Struts
AIRCRAFT 25
Figure 21 — Various Wing Shapes
^
Figure 22 — Possible Wing Locations
26 FUNDAMENTALS OF AVIATION AND SPACE TECHNOLOGY
Frgore 23 — Diagra curved ribs, cros
truction including the
Monoplanes may be classified according to the loca- tion of the wings on the fuselage and the shape of the wings. The wings, which may also be used to cany the fuel tanks and engines, may be mounted high, low, or in the middle of the fuselage and may be of several different shapes. (Figures 21 and 22.)
Wings
In general, wing construction is very similar in all types of airplanes. Briefly, the main structure of a wing consists of two long spars of aluminum alloy running outward from the fuselage end of the wing toward the wing tip. ( Figure 23. ) Curved ribs are secured to the spars and covered with thin aluminum alloy "skin" to give the wing its familiar curved shape. In the case of some light airplanes the spars are made of wood, and the skin is tightly stretched cotton or linen fabric which is painted with "dope" to give it a tough, weather resistant surface of the proper shape.
Wings are secured to the aiqilane fuselage by using one of two systems. The first is the full cantilever type in which the wing structure is made very strong and is fastened to the airplane fuselage without any exter- nal struts or wires.
The second system is the externally braced wing in which heavy struts or streamlined wires extend from the wing to the fuselage. In this case the wing may be of lighter construction than the full cantilever type, but the struts or wires increase the amount of drag and thereby reduce the speed of the airplane. The modern achievement of high-speed aircraft is partially due to the elimination of such external brac- ing as struts and wires. The externally braced wing construction is now used only on the slower and less expensive light planes.
As a part of the trailing edge, or rearmost part of the wing, and outboard toward the tips, are the ailerons, controlled by sideways pressure on the stick or by rotation of the control wheel. The purpose of
the aileron is to produce a rolling or banking motion. In the area of the trailing edge of the wing, between the ailerons and the fuselage of some airplanes, are the flaps. Flaps are hinged devices which vary the camber or curvature of the wing. ( Figure 24. ) Correct use of the flaps in flight is to steepen the gliding angle without changing the gliding speed. Flaps shorten the landing roll primarily by allowing a lower landing speed, not by adding resistance, although the latter is also a factor. In actual use, the flaps are often raised during the landing roll so that lift is decreased and more weight is placed on the wheels. This is done to give the tires better traction for their braking ac- tion. Flaps are usually used for resistance only under conditions of poor tire adhesion, i.e., ice or snow on the runway. They may be used during takeoff to increase the lift of the wing, thereby shortening the distance of the takeoff run.
Flaps are controlled directly by the pilot, using either a simple lever arrangement or, in the case of larger airplanes, levers actuated by a hydraulic pump or by an electric motor. Frequently the flap control sys- tem selected by the airplane manufacturer will also be used to raise and lower the landing gear. In the wings of some airplanes may be found slots, which are high-lift devices located in the leading edge of
AILERON
FLAP
AILERON
AILERON
FLAP
FLAP
Figure 24 — A drawing showing the location of flops which in a low ered position (as shown) will steepen the gliding angle and may resul in a shorter landing run.
the wing in front of the ailerons. Their function is to improve the airflow over the wing at high angles of attack, thereby lowering the stalling speed. (Fig- lue 25.)
Fuselage
The airplane fuselage is the main body of the air- plane and carries the crew, controls, passengers, and cargo. It must be constructed so that it has great strength for its weight, provides enough room, and has a proper streamlined or aerodynamic shape. The fuselage, called the hull in a flying boat (figure 26), may also contain the engine and fuel tank. An am- phibian is an airplane whose hull is equipped with retractable wheels to enable it to operate from either land or water. (Figure 27.)
Fuselages are classified according to the way in which the structure has been built. The two main types of construction are the truss and the semi- monocoque. (Figures 28 and 29.) The first is made of steel tubing; the second with an internally braced metal skin.
Regardless of the attitude or position of an air- plane, i.e., parked, taking off, landing, flying straight and level, turning, or performing acrobatic maneu- vers, there are always stresses on the fuselage struc- ture. The bracing of the welded steel-truss type acts like the structure of a bridge, since loads will be dis- tributed by the parts to the entire fuselage. The semi- monocoque gets its strength from the metal skin or shell which is reinforced by the internal bulkheads and stringers.
Tail Assembly
The empennage, or tail assembly of an airplane (figure 18), is composed of several parts, each of which has a definite control function. The horizontal stabilizer prevents the nose of the airplane from pitch- ing up and down. The elevator, a hinged portion of the horizontal stabilizer, controls the angle of attack. The vertical fin helps to maintain the diiection of flight. The rudder swings the nose right or left and, in conjunction with the ailerons, is used to make co- ordinated turns. These surfaces are of many sizes and
STALL
Figure 25 — Wing Slots Diagram. On the left side, the normal flow of oir over the wing is observed. Note the burble or breokdown of smooth flowing air in the stall condition without slots and then compare the
air flow over the slotted diagram on the right.
■ing at the same angle of ottock in the
28 FUNDAMENTALS OF AVIATION AND SPACE TECHNOLOGY
Figure 17 — Amphib wheels (retraclabl
Figure 28 — Welded Sleel Tubular Fuselage
Figure 29 — Semi-Monocoque Fuselage
Figure 31 — Tricycle Landing Gear
shapes, and there are many variations in positioning the vertical and horizontal elements.
Frequently, in discussing control surfaces, the term balanced control is employed. This merely means that the control, whether aileron, elevator, or rudder, is so arranged and operated that when the pilot moves any control some aerodynamic force is set in motion to assist him. Normally the pilot's strength would be the only force exerted in moving the control surfaces. However, when balanced controls are used, pressure of the air strikes the balanced section which is forward of the hinge, thus exerting a force on both sides of the hinge and making it easier for the pilot to move the control in the desired direction.
In very large airplanes, and those capable of super- sonic speed, it is necessary to give the pilot additional assistance in moving the controls. This is accomplished by the use of servo units, which are electrically or hydraulically operated mechanisms which move the control surfaces in response to the pressures imposed on the cockpit controls by the pilot.
AIRCRAFT 29
Figure 32 — Landing Gear Being Retracted
Landing Gear
An airplane's landing gear may be the conventional type, with two main wheels and a tail wheel, (figure 30), or it may be the tricycle type, with two main wheels and a nose wheel, ( figure 31 ) . The wheels may be fixed or retractable, i.e., folding into the fuselage or wings, (figure 32).
To take up the impact of the landing, the wheels of most airplanes are attached to oleo struts, which are shock-absorbing devices that use oil to cushion the blow. (Figure 33.) This type of shock absorber is located in the landing gear struts to which the wheels are attached, and is composed of an outer cylinder fitted over a piston. The piston is on the end of a short strut attached to the wheel axle. Between the piston and a wall or bulkhead in the outer cyhnder is a space
filled with oil. The impact of the landing pushes the piston upward, forcing the oil through a small opening in the bulkhead into the chamber above it, thereby cushioning the shock.
On some light airplanes tlie shock of landing is re- duced by the use of sltock cords. These consist of many rubber bands tightly bound into a bundle with a cloth covering. They tend to cushion the landing by stretching and thereby distributing the impact over a greater period of time. The same principle is em- ployed by other light planes equipped with landing gear struts made of spring steel. Just as the rubber shock cords stretch to give the effect of a soft landing, so the steel struts accomplish the same end by bending outward as the wheels make contact with the runway.
To aid in controlling airplanes on the ground, the main wheels are equipped with brakes which may be
30 FUNDAMENTALS Of AVIATION AND SPACE TECHNOLOGY
OUTER CYLINDER
Figure 33 — Principle of Oleo Strut Operation
operated separately or together. Brakes are used not only to slow up a fast rolling airplane but also as an aid to steering and parking. For example, pressure on the left brake and slightly advanced throttle will cause the airplane to turn to the left around the left wheel. As little use as possible is made of brakes, because the weight and speed of the airplane may result in over- heating and subsefjuent damage to the brake mech- anism.
Special types of landing gear include skiis for snow and ice and floats for water. For carrier landings, air- planes are equipped with an arrester hook that catches in a system of cables on the flight deck, bringing the airplane to a stop in a short distance.
Powerplants
Lack of suitable power retarded the development of the airplane for many years. After an adequate engine was devised it more than kept pace with the changes in the airframe structure.
A commonly-used powerplant is the internal com- bustion gasoline engine. This type of powerplant may
consist of as few as four cylinders or as many as twenty-eight. The cylinders of the smaller engines are arranged in a horizontally-opposed fashion, while those having more than six cylinders are arranged radially around the crankshaft. (Figure 43) The num- ber of individual engines required by an airplane is determined by the horsepower needed to provide the necessary thrust. WhUe a single engine may adequately supply the horsepower requirements for a small light plane, as many as foiu" may be needed on a large transport.
Engines may be mounted in several ways. The tractor type has the propeller attached to the front of the engine and pulls the airplane through the air. The pusher, as its name implies, pushes the airplane by having its propeller attached to the rear of the en- gine. Single, tractor-type engines are usually mounted in the nose of the fuselage. Airplanes with two or more engines may have their powerplants mounted in the wing, atop the wing, or under the wing.
Propellers
Converting the energy of the engine's revolving crankshaft into a pidling or pushing force is accom- plished by the propeller— a rotating airfoil providing the forward thrust for airplanes and airships. Propel- lers can have two, three, or four blades and can vary greatly in their configuration. Some have long slender blades, while others are broad, with short square-cut, paddle-like blades. Occasionally two counter-rotating propellers are driven by a single engine.
The propeller derives its pulling or pushing effect from the angle at which the blade is set on the hub. This angle is called pitch. The pitch or blade angle may be changed automatically, by mechanical means or by hand, in order to give the propeller its greatest efficiency. Low pitch, or a flat blade angle, provides higher revolutions per minute while high pitch, or a greater blade angle, gives lower revolutions. (Figure 34.)
Propellers are classed as fixed pitch, a blade angle that cannot be adjusted; adjustable pitch, a blade angle that can be changed only on the ground; con- trollable pitch, a blade angle that can be changed by the pilot from the cockpit; and constant speed, a blade angle that automatically adjusts itself according to the amount of power used. Some constant speed propellers may be feathered, i.e., their blades may be turned so that the leading edges are aligned with the line of flight. (Figure 35.) Feathering a propeller stops a disabled and vibrating engine, decreases the drag of the propeller, and increases the performance of the airplane while operating with the remaining engine or engines. (Figures 36 and 37.) Propellers may also
have reversible pitch for use as a landing brake. In this type, the blade angle is shifted to provide thrust in the opposite direction.
AIRCRAFT 31
Figure low ar (blade: each n
34-1 F.ne or low pitch, high RPM for take-off (blades have '9le of attock). 2. Coarse or high pitch, low RPM for cr.isir,q
''lZ% T.' °' °"°'''- ^ * « °^^ '•"-— -e dis.ar,ces that
lOves forward in one revolution
Figure 35— Full Feathering Propeller. In the left diagram the blades ore^set for normol operation while on the right the blades ore feoth-
A= CONSTANT SPEED PROP B=TWO P0SITK3N CONTR. PROP C= FIXED PITCH PROPELLER
Figure 36— Propeller Pitch Performonce Comparisons
j , FEATHERING
Figure
37— Feathered and Unfeathered Propeller Performance
Jet Propulsion
The jet engine usually eliminates the propeller and provides much greater speed than is possible with the propeller-driven, internal-combustion engine. The jet engme derives its thrust by compressing the air that IS drawn into the front of the engine and combining It with fuel which is then burned in the combustion chambers. The hot and greatly e.xpanded gases thus tormed develop tlirust as they are exhausted out of the tail pipe. A portion of the power formed by the burn- ing exhaust is used to turn a turbine wheel which drives the compressor and other components. The one e.xception to the elimination of the propeller is the turbo-prop engine, which not only gives forward thrust with Its blast of hot air but also gains additional thrust from a propeller. (See Chapter V.)
The jet engine is now widely utilized by the mili- tary services, and speeds far in excess of the speed of sound are commonplace with jet-propelled military au-craft. Like the internal-combustion engine, the jet
FUNDAMENTALS OF AVIATION AND SPACE TECHNOLOGY
powerplant is frequently mounted in the wing, but it is also occasionally suspended below the wing, where it is held in place by a mounting structure called a pylon. In the modem jet fighter the engine is usually located in the fuselage behind the pilot.
Airplane Accessories
Many devices are in use today to insure the comfort and safety of the passenger and the crew. Many of these devices are electronic in nature, such as the auto-pilot, which will dutifully perform the work of the pilot by flying the airplane and keeping it steadily on course. Various other devices are sensitive to the presence of fire or smoke in remote areas such as the cargo compartment and will immediately sound an alarm when such danger occurs.
Among the mechanical accessories used on military and commercial airplanes are de-icer boots. (Figure 38.) These consist of flexible rubber sheets containing inflatable elastic tubing and are mounted in the lead-
Figure 38 — De-icer Boot Operation. In the top drawing, rime ice has formed. In the center, the upper ond lower boot sections have ex- panded, cracking off the ice. In the bottom view, the center boot por- tion expands, the top and bottom sections collapse, thus completely removing the ice.
ing edge of the wing and tail surfaces. When inflated and deflated at regular intervals, they distort and stretch the leading edge of the boot in such a manner that ice formations crack and blow away. Many metal aircraft now use an internal heater, located inside the wing just behind the leading edge, which, when acti- vated, heats the metal skin and melts any ice which may have formed. To combat ice formations on the propellers a "slinger" ring may be installed. This dis- tributes de-icing fluid along the blades while in flight, loosening any ice that may have formed and prevent- ing further formation.
Commercial airliners are equipped with cabin pres- surization equipment. This equipment can maintain a simulated altitude of two or three thousand feet even though the aircraft itself may be flying at twenty thousand feet, thereby providing an atmosphere with enough o.xygen to prevent drowsiness in the crew and permit comfortable breathing by the passengers.
Other Aircraft Types
Other types of aircraft include the rotary, lighter- than-air craft, ornithopter, and the convertiplane. There are two general types of rotary aircraft— the helicopter and the gyroplane.
The rotor blades of the helicopter are merely re- volving wings, getting their lift from the motion of air over a curved surface in the same manner as the wing of an airplane. The revolving blades create an up- ward force (lift), and if they are tipped, the heli- copter will move in the direction in which the blades have been tipped. ( Figure 40. )
Due to the rotation of the blades in one direction, the helicopter fuselage tends to revolve in the opposite direction. To counteract this tendency, the helicopter is usually equipped with a small propeller on the tail which directs a blast of air sufficient to overcome the effects of this torque or turning motion. By increasing or decreasing the pitch of the blades of this tail rotor, the pilot can control the direction of forward motion. Other types of helicopters overcome the undesirable effects of torque by incorporating two sets of counter- rotating blades. This also provides for a greater lifting force and is now commonly used on the larger models.
The helicopter is unique because it can hover over one spot, and for this reason can take off or land in a space not much larger than the diameter of the rotor blades. A free-wheeling device attached to the rotor drive shaft allows the rotor blades to act like those of an autogiro by lowering the craft gently to the earth in the event of engine failure.
The gyroplane has unpowered, overhead rotating blades for ordinary flight. These blades may be geared
AIRCRAFT 33
to the engine for jump takeoffs. Forward flight in an autogiro is accomplished by the use of a conventional aircraft engine and propeller.
There are three general kinds of airships— the non- rigid, the semirigid, and the rigid. The nonrigid air- ship has a streamlined, gas-tight rubberized envelope or skin which is not supported by a framework nor reinforced by any stiffening materials. It maintains its shape by the internal pressure of the gas within the envelope. Blimps are the typical example of this type of airship.
The semirigid airship has a structural metal keel and a metal cone to strengthen its bow. This reduces the bending strains on the envelope and tends to keep the airship in its inflated shape lengthwise. The en- velope still has to be kept in its flying shape by the pressure of the gas within it.
If inside framework is used to support the gas envelope and the airship is not dependent upon the inside pressure of the gas to maintain its shape, the airship is said to be a rigid type. Since 1938 there have been no known rigid-type airships constructed.
An airship flies because of its lift and thrust. The lift comes from the lighter-than-air gas which raises the airship into the air. The hull of the airship pro- vides a large enclosed space in which the lifting gas can be contained. Often the space will be divided into separate compartments for the gas. These compart- ments are called balloonets.
Thrust, the force wfiich moves the airship through the air, is obtained usually from the engines and pro- pellers which are often located in gondolas or cars suspended from the hull. These are sometimes called "power eggs."
All airships, either inside or outside the hull, carry a car or keel structure, usually of metal, to provide space for personnel and cargo, in addition to storage room for fuel and equipment.
Control of an airship is by certain fixed and movable surfaces, usually at the stern of the airship, which help guide the airship in the same general way as do the rudder and elevator of an airplane. Usually the con- trols are directed from the control car by connecting cables.
An ornithopter is an aircraft designed to fly or propel itself through air by means of flapping wings. This idea is the oldest in the history of flying. Man naturally first turned to the flight of birds for ideas to aid him in his own desire to travel through the air. While some small-scale models have flown, no success- ful man-carrying ornithopters have been developed.
All ornithopters, no matter how varied in design, may be classified in two ways. The first type uses various forms of wings for support in the air and
Figure 39— X-18 IN FLIGHT TESTS— Shown is the Id'/j Ion XI 8 dur- ing flight tests over Edwords Air Force Base, Calif. Wings have reached on angle of oltock of 50 degrees during flight. Now in a ground pro- grom to study the effects of downwash during simulated hovering, the X-18 is expected to be back in flight tests at a loter date for full hovering and vertical operation.
fastens the wings to the body of a man. The second type uses a cabin or cockpit to house the pilot. To it the flapping wings are attached and from it the wings are operated.
Early experimenters used the first method. Most came to the conclusion that the strength of birds was much greater in relation to their weight than man's strength in relation to his weight and that it would be impossible for man to fly by his own strength alone. However, experimenters are still working on this problem.
A convertiplane is an aircraft so built that it can perform, at the will of the pilot, as any one of two or more types of aircraft. Some types may be ad- justed to fly either as a helicopter, autogiro, or fixed- wing aircraft. Aircraft that are essentially converti- planes are often called STOL aircraft, meaning that they require only a short take off and landing run. Still others are referred to as VTOL as they can actually take oflF and land vertically. (Figure 39.)
There are two basic types of convertiplanes. The first type looks more like the typical airplane and uses the same source of power for forward motion that it does for rising vertically or hovering. Thus it may rotate its propeller or propellers, or even the whole wing structure, from the horizontal to the vertical, to change from forward motion to hovering flight or a straight-down landing.
40 — Helicopter
34 FUNDAMENTALS OF AVIATION AND SPACE TECHNOLOGY
©
Figure 41 — Aircraft Safetying Methods
The second type of convertiplane resembles the hehcopter more than it does the fixed-wang aircraft. In this type, the rotor axis remains vertical. In for- ward flight the rotor blades may be fixed in place, allowed to revolve without power, locked in a trail- ing position, or folded into the fuselage. These types require a propeller or other means for forward propulsion.
Convertiplanes usually are powered by the same type gasoline or jet engines used by other civil and military aircraft. If the convertiplane is using small jet engines, it may vary the position of the engines, or use diversion valves, so that the thrust will be in the direction desired.
Aircraft Construction
Modern military and commercial airplanes are con- structed chiefly of aluminum and aluminum alloys. Other metals such as magnesium, titanium, copper, and the many alloys of steel, have characteristics which lend themselves well to the construction of various aircraft components. Metal parts are joined by riveting, welding, soldering, brazing, and special adhesives. Parts designed for future disassembly are fastened together with nuts, bolts, and screws, or other similar devices. Such hardware as nuts, bolts, and turnbuckles must be secured so they cannot be- come loose during flight. (Figure 41.) This precaution is called safetijing, and is accomplished with cotter pins, safety wire, airplane safety pins, and elastic stop nuts.
Some light airplanes have components made of wood such as spruce, fir, or pine. These woods are particularly useful because of their strength-weight ratio. Other components require the stiffness that is to
be found in birch, mahogany, or ash. Wooden parts are fastened together with nails and resin or casein glues. Cotton or linen fabric, aluminum or aluminum alloys, and fiber glass are normally used to cover the frame of the airplane.
Many other materials are required in the production of the modern airplane. Of these, the family of plastics is playing an ever-increasing role. Synthetics are now found in carpet and upholstering materials, windows, cable pulleys, electrical insulation, paints and finishes, and in many other airplane accessories. In addition, such materials as glass, asbestos, leather, rubber, cot- ton, and many others have characteristics of some particular value in the construction of the airplane.
Aircraft Inspections
A program of regular inspections is required of every airplane. This government-enforced policy tends to insure the continued airworthiness of the airplane and is a major factor in the enviable safety record established by modern aviation. At intervals not to exceed one year the condition of the entire airframe and powerplant and all their components is carefully examined. In addition to this, all aircraft used as air carriers must be submitted for similar inspections, determined by the amount of flight time accrued. At regular intervals between these periodic inspections are others, less detailed in nature and completeness. All inspections necessitate the skill and knowledge of the airframe and powerplant mechanic, who is re- quired, by law, to certificate the work he has com- pleted.
Finally, every airplane should have a preflight in- spection in order to maintain further the efficiency and safety of the structure, engine, equipment, and accessories. Inspection procedure should include the powerplant, landing gear, wings, tail assembly, and fuselage. Such an inspection is normally the responsi- bility of the pilot, or, in the case of a large transport aircraft, the flight engineer.
The following is a general preflight check list. In addition to this list, each type of airplane requires its own particular list.
A. Propeller
1. Inspect blades for pits, cracks, and nicks; in- spect hub(s) and attaching parts for defects, tightness, and safetying.
B. Engine
1. Inspect engine cowling, exhaust stacks, and col- lector rings for cracks and security.
2. Check spark plug tenninal assemblies for clean- liness and tightness; check accessible ignition wiring and harness for secmity of mounting.
AIRCRAFT 35
Figure 42 — The cockpit section of the Link 707 simulator is on exact replica of the flight cJeck of the actual aircraft. This photo, taken from
behind the pilot and co-pilot seots, shows the complete of instruments and controls found in the simulator.
3. Check all bolts and nuts on engine mount.
4. CHECK FUEL AND OIL SUPPLY, making certain that the vent openings are clear and the tank caps are on tight.
C. Landing Gear
1. Inspect tires for defects and proper inflation.
2. Inspect wheels for cracks and distortion; in- spect the brake-actuating mechanism for se- curity and cleanliness.
3. Inspect the landing gear attachment bolts; in- spect the struts for proper inflation.
D. Wings
1. Inspect the metal or fabric covering for such damage as holes, dents and wrinkles; check attachment fittings for security.
2. Check struts and flying wires for security of terminal connections; check aileron hinges, pins, horns, and tabs.
3. Inspect all accessible control cables, tubes, and pulleys for security.
E. Empennage
1. Inspect the covering for damage, the edges for dents and distortion, and the fittings for se- curity. 2. Check struts and brace wires for security of terminal connections; inspect control surfaces, hinges, pins, horns, and tabs.
3. Inspect control cables, tubes, and pulleys for security and lubrication; check the tail wheel assembly for general condition and security.
F. Fuselage
1. Inspect the covering for damage and distortion and check the windows, windshield, and doors for security and cleanliness.
2. Check all removable cowling, fairing, and in- spection plates for security.
3. Check the control column, rudder pedals, and trim mechanism for security of attachment and freedom of movement.
4. Check the proper functioning of the lighting
36 FUNDAMENTALS OF AVIATION AND SPACE TECHNOLOGY
system and the location of the spare fuses or circuit breakers. 5. Inspect for security of safety belts and the proper functioning of adjustable seats. G. Warming Up
1. See that chocks are under the wheels.
2. Be certain that the master switch is OFF before turning the propeller over by hand; be sure that the front is "clear" before using a starter.
3. Check position of the gasoline shut-off valve, carburetor heat control, and carburetor mix- ture control.
4. Test engine(s) on each magneto and on all " tanks.
5. Check radio equipment for proper functioning.
6. Note oil temperature, pressure and rpm.
Supersonic Transport
The newest development in civil aircraft design is the supersonic transport, generally spoken of as the SST. This could cut flight times at least in half. The British and French governments are working jointly on an SST, which is expected to be in the Mach 2 range (1,200-1,400 mph) and available by 1971. It is also known that the Russians are working on such an aircraft. Both developments are for relatively short-range aircraft.
The United States is planning a longer-range and faster SST. Its range is to be about 4,000 miles and the speed will be up to Mach 3 (1,800-2,000 mph). This is a joint industry-government project and is planned for service about 1972. One of the engineering developments expected in the SST are wings which can be adjusted to the speed desired, thus providing lower landing speeds and more efficient lift.
Summary
Aircraft are divided into two classes: (1) heavier- than-air and (2) lighter-than-air. Present-day em- phasis is on the heavier-than-air craft, particularly the airplane. The helicopter, autogiro, omithopter, and convertiplane are other types of heavier-than-air craft.
The major sub-assemblies of the airplane's structure are (1) wings, (2) fuselage, (3) tail assembly, (4) landing gear, and (5) powerplant. Airplanes having one wing are called monoplanes; those with two wings are called biplanes. Aerodynamically, monoplanes are more efficient.
The framework or structure of the wings, fuselage, and tail surfaces is relatively light because of the kinds of metal used, and very strong because of the manner
in which individual internal members of the structure are formed and fabricated. The structure is covered with either doped fabric or sheets of very light metal.
The fuselage houses the crew, controls, cargo, and passengers. Occasionally the powerplant and the fuel tanks are mounted in the fuselage. The engines in a multi-engine plane are mounted on the wings, the powerplant supporting members being attached to the main spar or spars. Engines and propellers can be of the tractor ( pull ) type or of the pusher type.
The term undercarriage refers to the structure or mechanism upon which the airplane rests when it is not airborne. In the case of land planes, it consists of wheels and struts mounted to the structure to absorb the shock of landing. The wheels are equipped with brakes to stop the landing roll and to facilitate ground handling. The undercarriage may be of the fixed type or may be completely retractable.
The tail assembly consists of vertical and horizontal airfoils, both fixed and movable. These surfaces vary in size, shape, and arrangement, according to the de- sign of the particular make of airplane. The movable surfaces are controllable from the cockpit, and in con- junction with the ailerons serve to determine the flight attitude of the airplane.
Propellers may have two, three, or four blades. The effectiveness of the propeller (which is actually an airfoil) is computed from the number of revolutions per minute (rpm) and the angle at which the blades are set. This angle is called pitch and may be fixed, adjustable, controllable, or constant speed. Simple wood or metal propellers with no moving parts have a fixed pitch. Low pitch means that the blades are attacking the air at a relatively flat angle. Low pitch is used during takeoff (if the propeller pitch is con- trollable ) because greater power is obtained that way. High pitch means that the blades are attacking the air at a relatively large angle. If the pitch is controllable, high pitch is used at cruising speed.
Airplanes are constructed of materials having light weight and great strength. These include the alloys of aluminum, steel, and magnesium. In some light planes such woods as spruce, fir, and pine are used for struc- tural members, and the covering is made of cotton or linen fabric which is coated with dope to make it taut and weather resistant. The metal parts are joined by such techniques as welding, brazing, and riveting, while glue is used for fastening together the parts made of wood. All aircraft hardware such as bolts and nuts is secured by various methods of safetying.
To insure safety in flight, every airplane must under- go regular inspections. Of these, the preflight inspec- tion is the most common and is usually performed by the pilot. Much more complete inspections are per- formed periodically by the airplane mechanic.
AIRCRAFT 37
Questions
1. Identify the five major components of an air- plane and explain the purpose of each.
2. Briefly describe the construction of a wing, and explain the two methods of attaching and brac- ing the wings of the fuselage.
3. Identify the ailerons and the flaps and explain the purpose of each.
4. In what area of the wing are slots located, and what is their purpose?
5. Name and describe the two main types of fu- selage construction.
6. List the major components of the empennage.
7. Of what value to the pilot are balanced controls and servo units?
8. Explain how the effect of a soft landing is achieved by the various types of landing gears.
9. Differentiate between the tractor and pusher types of aircraft.
10. What types of engines are used to power air- planes, and in what positions are they located on the airframe?
11. What are the different types of propellers and what advantages are to be derived from chang- ing propeller pitch?
12. Explain the purpose and operation of de-icer boots.
13. List some of the accessories that make for safer and more comfortable flight.
14. How is forward motion accomplished with a helicopter and with an autogiro?
15. What are the three general types of airships?
16. What are the two basic types of convertiplanes?
17. List some of the materials that are used in air- plane construction and describe how these mate- rials are fastened together.
18. What is the purpose of safetying aircraft hard- ware?
Chapter H
The Aircraft Engine
Man's failure in his early attempts at flight were due primarily to two obstacles: insufficient knowledge of the basic principles of aerodynamics and the lack of a suitable source of power. The second obstacle was the last to be overcome. Several pioneers attempted flight using only their own power, but it soon became apparent that man was not sufficiently powerful to lift and propel himself in flight— with or without the most efficient aerodynamic devices. The requirements were obvious— an engine must be built which was capable of producing considerably more power per unit of weight. The solution called for use of lighter, stronger materials, new engine design to eliminate unnecessary parts and weight, and possibly a new fuel.
The first partial solution was (juite crude though the operating principles of this engine, built by the Wright brothers in 1903, are still used in our present recipro- cating or piston-type engines. The Wright engine's shortcoming was its relatively high weight per horse- power. With a weight of about 180 pounds and an output of approximately 30 horsepower, it developed only 1/6 horsepower per pound. Continued research in the use of lighter materials, more powerful fuels, the principle of supercharging, and more efficient arrangement of cylinders has since increased the ratio of horsepower to weight in reciprocating engines to appro.ximately one horsepower per pound. When the aviation industry demanded a more powerful engine, the jet or "reaction" engine was developed. The jet engine is capable of producing several horsepower per pound of weight at high speeds.
Aircraft Engine Requirements
Although the fundamental aircraft engine recjuire- ment is still the same as when the Wright brothers built their engine— as much power as possible from a given weight— the airplane engine may vary accord- ing to the purpose for which the plane is intended. Some types of engines are more suited to light private
ROW TYPE
Figure 43 — Aircraft Engine Cylinder Arranger
THE AIRCRAFT ENGINE 39
airplanes, others better suited for civilian transports, and still others more adapted to military aircraft.
Regardless of size, type, or principle of operation, all aircraft engines possess certain mutual characteris- tics. These characteristics are:
( 1 ) development of a reasonably large amount of power for a given weight,
(2) reliability and performance at various speeds,
(3) fuel and oil consumption compatible with power produced,
( 4 ) lack of excessive vibration,
(5) relatively easy maintenance.
Aircraft Engine Types
Installation of the engine in the airplane raised several new problems including cooling and stream- lining. To overcome these problems, wliile fulfilling the previously mentioned requirements, manufacturers have designed engines with many different cylinder arrangements. ( Figure 43. ) One of the first air-cooled radial engines was a French rotary type, i.e., the cylinders and crankcase revolved around a stationary crankshaft. The French rotary type engine had good cooling characteristics, but because of excessive vibra- tion, it became obsolete. The most commonly used engines have their cylinders arranged parallel to each other in tandem (in-line), in two tandem rows at ap- proximately right angles (V), in two rows on opposite sides of the crankshaft (flat or horizontal opposed), or like spokes of a wheel around a central shaft ( radial ) .
SPARK PLUG
COOUNG FINS
Figure 44 — Types of Crankshafts
CRANK SHAFT
Courtesy Wright Aeronautical Corp. Figure 45 — Front View of 9-Cylinder Radiol Engine
Because cooling difficulties more than offset stream- lining advantages of the in-line and V-type engines, most modern reciprocating engines are horizontally opposed or radial. Opposed engines are used in almost all light aiiplanes, including small twin-engine planes where the engines are "buried" in the wings. The number and the size of the cylinders used in opposed engines are so limited by cooling problems and crank- shaft design that opposed engines rarely exceed 250- 300 horsepower. Larger airplanes, requiring more power, use radial engines— some with two or four rows or "banks" of cylinders. Such engines can develop in excess of 3,.500 horsepower per engine. When even more power is needed, engines are used in pairs, in groups of four, or as many as six or eight per plane. However, more power per engine requires a different type— the jet or rocket.
Aircraft Engine Parts
Some knowledge of the parts of an engine is pre- requisite to understanding its principles of operation. (Figures 44, 45 and 46.) The main function of the crankshaft is to change reciprocating motion into rotary motion. The force of the expanding gases on the top of the piston is transmitted to the crankshaft thiough the connecting rod or a link rod. The type of crankshaft varies with the engine. A single row radial engine uses a crankshaft with one throw or crank, about which a master rod is fitted. Link rods connect this master rod with all of the cylinders except one—
40 FUNDAMENTALS OF AVIATION AND SPACE TECHNOLOGY
Figure 46 — Cutaway View of Twin-Row Radial Engine
the master rod cylinder. An in-line or opposed engine normally uses a crankshaft with as many throws as it has cylinders and with a connecting rod between each cylinder's piston and its respective crank throw. The crankshaft may be connected directly to the propeller, or through reduction gears which slow the rotation of the propeller relative to the crankshaft. The cylinder head is forged or cast aluminum and is threaded and then shrunk onto a steel cylinder barrel which has a hardened inner wall. The intake valve has a solid stem, while the exhaust valve may be hollow and filled with metallic sodium to improve the heat transfer to the cylinder. Cooling fins on both head and barrel aid in keeping cylinders below dangerous tempera- tures. Piston rings help prevent loss of gas pressure above the piston during compression and power development.
The Four-Stroke Cycle Principle
Reciprocating engines operate by repeating the same cycle of events in each cylinder, i.e., (1) a charge of fuel and air is forced into the cylinder,
(2) the charge is compressed, (3) the charge is ig- nited, (4) power is obtained from the expanding gases, and (5) the burned gases are expelled. The first event may differ somewhat in diesel engines or in those equipped with direct fuel injection, but,
PISTON RINGS
CONNECTING
COOLING FINS
VALVE GUIDE
CYLINDER HEAD
Figure 47 — Airplane Engine Cylinder Nomenclatur
Figure 48— Val
THE AIRCRAFT ENGINE 41
fundamentally, the same events are present. These are sometimes called: (1) intake, (2) compression, (3) ignition, (4) power, and (5) exhaust. Most en- gines require two complete revolutions of the crank- shaft or four strokes (a movement of the piston from top dead center to bottom dead center in the cylinder, or vice versa, is called a stroke) to complete all five events in the cycle. Such engines are called four- stroke cycle engines, or sometimes four-cycle engines.
Two valves, operated by a cam shaft or a cam ring and a connecting linkage, are required in each cyl- inder to complete this cycle of events. (Figure 47.) The gears actuating the valve-operating mechanism and the magneto are correctly meshed with those on the crankshaft to give correct timing to these events. (Figures 48 and 49.)
In more detail, the five events in a complete cycle are:
1. Intake. With the e.xhaust valve closed and the intake valve open, the piston moves downward in the cylinder, reducing the pressure therein and causing air ( and fuel, if a carburetor is used ) to flow through the induction system into the cylinder.
2. Compression. The intake valve closes shortly after the piston passes bottom dead center, and the
EXHAUST INTAKE
^^ ^ ^ ^ ^
INTAKE
COMPRESSION
IGNITION
POWE R
EXHAUST
Figure 49 — Slages of the Four-Slroice Cycle Engine
42 FUNDAMENTALS OF AVIATION AND SPACE TECHNOLOGY
Figure 50 — Diogram Showing the Radial Engine Lubricolion Syslen
fuel and air charge is compressed as the piston moves toward top dead center.
3. Ignition. A high-voltage current flowing from the magneto through the distributor at the correct instant, usually 20° -30° before top dead center, jumps a gap in the spark plug and ignites the fuel charge.
4. Power. The burning gases create very high pres- sures inside the cylinder and after the piston has passed top dead center (carried there by momentum or the force on other pistons) it is forced down, caus- ing the crankshaft to rotate.
5. Exhaust. When the piston approaches the bot- tom of the cylinder, the exhaust valve opens and stays open almost three-fourths of a revolution, thus permit- ting the burned gases to be forced out by the upward travelling piston.
The complete cycle is repeated appro.ximatcly 1,000 times by each cylinder during every minute of opera- tion. An eighteen cylinder engine gets its power from approximately 300 power strokes per second.
Engine Systems
Although the engine functions as a complete unit, its operation is more easily studied by a breakdown into smaller functions, or systems. This breakdown would include the lubrication, fuel and induction, ignition, and mechanical systems. The mechanical system is composed of cylinders, pistons, valves, etc..
and has already been discussed in the four-stroke cycle principle. The lubrication system, besides per- forming the obvious and necessary function of lubri- cating the moving parts of the engine, has several other responsibilities, e.g., helps to cool the engine, provides for a better seal between piston rings and cylinder walls, prevents corrosion, and actuates hy- drauhc units such as valve lifters and propeller con- trols. (Figure 50.) Aircraft engines use a pressure lubrication system in which oil is pumped through drilled passages to the many engine parts which re- quire lubrication. Other parts, such as cylinder walls, piston pins, and some roller or ball bearings, receive oil by splash and spray. The oil supply may be car- ried either in the engine's crankcase (wet-sump) or in an external tank (dry-sump). Most opposed-type enj^nes are the wet-sump variety, but radial engines are always dry-sump. The dry-sump engine is so called because the oil which settles into the sump (collection place) is pumped back to the external tank as quickly as possible by a scavenging pump. If the external tank is very large, as in a large airliner, a small hopper tank within the main supply tank re- ceives the oil pumped from the engine by the scav- enger pump for recirculation within the engine. When the supply of oil in the hopper tank drops below the level of that in the main tank, additional oil is added from the main supply. Several benefits derive from the use of a hopper tank, the most important being a more rapid warm-up of the engine.
THE AIRCRAFT ENGINE 43
FUEL AND INDUCTION SYSTEM
Internal combustion engines must be supplied with the correct mixture of fuel and air, which is taken into the cylinders, compressed, ignited, and burned to sup- ply power. This process may be accomplished by use of a fuel injection system which includes an air- metering device, or a carburetor, in which air and fuel are properly mixed before entering the intake mani- fold and cylinders. (Figure 51.)
The carburetor must be able to provide the proper mixture (about one part of fuel to fifteen parts of air, by weight) at all speeds. The correct mixture requires: ( 1 ) an idling system when the throttle is almost closed; (2) a main metering system for all other throt- tle positions; (3) an accelerating system to prevent temporary lean mixtures upon rapid acceleration; (4) an economizer system to supply extra fuel at higher engine speeds; and (5) a mixture control to allow for different air densities.
The throttle controls air flow through a restriction or venturi, in which a fuel discharge nozzle is placed. Increased air velocity causes a pressure drop, and fuel then flows from the discharge nozzle into the air stream. A wider throttle opening permits faster air flow and more fuel to be discharged.
Fuel must be vaporized and mixed with the oxygen in the air before it can burn. .As fuel vaporization
occurs, the mixture's temperature drops, sometimes as much as 60° F. Water vapor in the air may be condensed and frozen, even when outside air tem- peratures are as high as 80° F. Ice may collect on the butterfly valve (throttle) of the carburetor or in the intake manifold and, if allowed to build up, will cause engine stoppage. Carburetor ice is usually prevented by a carburetor air heater, which sends air, heated by the exhaust stacks, through the carburetor. Excessive use of the carburetor air heater may cause loss of power, or detonation; consequently carburetor heat should be used only when required.
At higher altitudes, the difference in pressure be- tween the inside of the cylinder on the intake stroke and the outside atmosphere may be so small that air and fuel flow into the engine are greatly reduced without some help. Full fuel and air flow are restored by a supercharger; in fact, the density of the intake charge may be increased to more than twice that obtained by an unsupercharged engine at sea level. The supercharger is a centrifugal pump which forces more air-fuel mixture into the cylinders. It may be internal, driven by a gear train connected to the crank- shaft, or external, driven by the exhaust. The external type is called a tiirbosupcrchargcr. (Figure 52.) Most of the larger radial engines have internal or integral superchargers, which have the additional responsi-
THROTTLE PRESSURE RELIEF VALVE
VALVE
FINGER FLOAT STRAINER CHAMBER
MAIN DISCHARGE NOZZLE
AIR INTAKE
Figure 51 — A t/pical aircraft fuel system showing how the gasolii pumped from the fuel tank into the carburetor float chamber, d
out of the main jet by suction, and, in an atomized or vaporized form, flows inside the intake manifold to the intake valve of the cylinder.
44 FUNDAMENTALS OF AVIATION AND SPACE TECHNOLOGY
bility of providing an even distribution of fuel to all of the cylinders.
IGNITION SYSTEM
The compressed fuel-air mixture is ignited in the cylinder, at the correct time, by a spark from a spark phig. (Figure 53.) The spark is caused by a high- voltage current developed by a magneto. ( Figure 54. ) As the permanent magnet rotates, a fluctuating mag- netic field is developed in the pole shoes, around which both the primary and secondary coils are wound. The changt in magnetic field creates a low-voltage current in the primary circuit, which includes, besides a coil with a relatively few turns of fairly heavy wire, a condenser, a switch, and a set of breaker points. The primary circuit is interrupted by the breaker points aided by the condenser at the most opportune time to cause a very rapid collapse in the magnetic field through the pole shoes. As a result, a high-voltage cur- rent is induced in the secondary circuit, which in- cludes, besides a coil with many turns of fine wire, the distributor, ignition leads, and spark plugs. The distributor causes current to flow to the spark plugs in the correct sequence, or firing order. An aircraft engine usually has two complete ignition systems, with two magnetos and distributors and two complete sets
WASTE GATE EXHAUST GASES
Figure 53 — A Simplified Cutaway Drawing of a Spark Plug
of spark plugs, not only for better ignition, but also as a safety factor.
ACCESSORIES
Accessories include those items which aid an en- gine's operation, but do not necessarily cause it to function. All large engines, and many smaller ones, are equipped with electric starters which are usually powered by a storage battery. A second accessory, the generator, is required to recharge the battery that also provides power for lights, flap and landing gear actu- ating motors, radio equipment, etc. Other accessories found on many engines include vacuum pumps for operating certain instruments, and propeller governors which control propeller blade pitch to maintain a con- stant engine speed through wide variations in throttle setting.
DISTRIBUTOR BLOCK" DISTRIBUTOR FINGER SECONDARY WINDING PRIMARY WINDING CONDENSER
FOTH OF MAGNETIC FLUX THRU MAGNET
Figure 52 — Culawoy View of o Turbo Supercharger
LPOLE SHOES'' ROTATING MAGNET Figure 54 — Schematic Diagram of an Aircraft Engine Magneto
THE AIRCRAFT ENGINE 45
Power Factors
Fundamentally, an internal combustion engine changes heat energy into mechanical energy and its power depends upon the rate at which it can do work. Three factors are involved in power devel- opment, (1) engine size or piston displacement, (2) speed of rotation, and (3) the amount of pres- sure on the piston.
PLAN
The horsepower formula is: H. P. = . "P"
33,000
is the effective pressure on the piston measured in pounds per square inch. "L" is the distance, measured in feet, which the piston moves from top dead center to bottom dead center (stroke). "A" is the cross- sectional area of the cylinder in square inches. "N" is the number of power strokes which the engine has in one minute. The constant divisor of 33,000 is used because one horsepower is defined as that power required to perform 33,000 foot pounds of work in one minute.
For example, a nine-cylinder engine with a 6-inch Cylinder diameter (bore), a 6-inch stroke, turning at 2200 rpm with a mean effective pressure of 160 pounds per square inch will develop horsepower at the rate of 160 X 1/2 X 32 X 3.1416 X 9900 33,000 or about 680 horsepower. Everything in the substitu- tion should be obvious with the possible exception of the value of "N", which was 9900. This value is obtained from the fact that in two complete revolu- tions of the crankshaft of any four-stroke cycle engine, each of the cylinders should deliver one power stroke. Therefore, a nine-cylinder engine rotating 2200 times
2200
per minute should have 9 X or 9900 power
2
strokes in one minute.
Modern Powerplants
Jet and rocket propulsion devices are often called reaction engines because their thrust is produced as a result of a reaction to an action. Perhaps the best explanation of the effect is a comparison with a more familiar occurrence, propulsion by a propeller driven aircraft.
Figure 55 shows a typical engine nacelle and pro- peller. Anyone who has been behind such an engine when it is operating knows that a large amount of air is being pushed to the rear with a high velocity. According to Newton's third law, for every action there is an equal and opposite reaction. In this in- stance, a force is being produced on the propeller
Figure 55 — Typical Reciprocating Engine-Propeller Combination
and engine combination in the opposite direction from that in which air is being thrown by the propeller. This combination might be called a "reaction engine." Figure 56 shows the same items as above, except they have been enclosed in a tube, and the air- flow is directed to the rear through this tube.
Figu.
Tube
56 — Reciprocating Engine-Propeller Combination Enclosed
46 FUNDAMENTALS OF AVIATION AND SPACE TECHNOIOGY
In figure 57 the engine-propeller combination has been replaced by a turbine wheel at the rear, a com- pressor at the front, and combustion chambers in which fuel and air are burned between the two. This combination causes air flow through the tube in the same manner as the engine-propeller combination in Figure 56. The mass of air being moved in this arrangement may be less but the final velocity of the moving gas is much greater and the resultant tlirust can be much greater. This thrust is the reaction, which was caused by the action of air moving toward the rear, and is transmitted from the component parts of the engine through its frame to the aircraft.
COMBUSTION CHAMBER
COMPRESSOR
Figure 57 — Compressor-Turbine (Typical Turbojet Engine)
TURBINE
The same result-a high-velocity flow of gases— is accomplished in the engine shown in figure 58 by burning fuel inside a container which is open at only one end. Such a device is called a rocket.
Thrust is NOT the reaction of the e.xpelled gases upon the air outside the engine. Thrust would be the same if the gases were being expelled into a vacuum. Thrust depends upon: (1) the mass of gas being moved, and (2) the velocity with which it is expelled from the exhaust or tail pipe. Technically, the second factor is the change in the velocity of the entering and leaving gases, but it is sufficient for our purpose
to consider only final velocity. The mass of gas being moved is increased by forcing as much air as possible into the inlet section of the engine. The velocity is increased by heating and expanding the air and by burning the fuel which has been mi.xed with it, then expelling it through a restricted exhaust passage.
Three types of jet engines may be considered, al- though only one merits much discussion at present. The most simple of the jet engines is the ram jet, or athodijd (a contraction of aero thermodynamic duct). ( Figure 59. ) It is often called a "flying stovepipe" be- cause it consists of a tube into which fuel is injected, burned, and then the hot gases expelled from the tail pipe. The "catch" is that the air which enters this jet must be compressed by the ramming action of the device itself. Consequently, it wOl not operate until it has reached a very high velocity— at least 500-600 miles per hour. It can be used to power helicopter rotors, as an auxiliary powerplant in an aircraft which has another engine to bring the aircraft up to the required speed, or in some other limited applications.
Jl
.^SPARK PT.UG
^COfcaOSTION SECTION
Figure 59 — Schematic Diagram of a Rom Jet Engine
The pulse jet (Figure 60) is almost as simple as the ram jet, except for the addition of automatic shutters in the inlet section. These shutters open as the engine moves through the air thus permitting air to enter the inlet opening. The shutters close when fuel, which has been injected into the same section, bums and causes the air to heat and expand. The heated gases
Figure 58 — Simple Rocket Engine
Figure 60 — Schematic Diagram of o Pulse Jet Engine
THE AIRCRAFT ENGINE 47
Figure 61 — Cutaway View of a Turbojet Engine
are then forced out the rear at high velocity. The drop in pressure, as the gases leave the exhaust section, again forces open the shutters, and the same cycle is repeated as often as 50-60 times per second. Although the pulse jet is simple to build, it loses efficiency at high speeds and is exceptionally noisy. There have been some military applications of this engine, notably the German "buzz bomb" of World War II, but its disadvantages are such as practically to eliminate it from commercial use.
The third, and by far most important commercially, is the turbojet. This classification is sometimes further subdivided into ( 1 ) the pure jet engine, without a propeller (Figure 61), and (2) the turboprop engine, which incorporates a propeller driven by the main shaft through a reduction gear train.
Turbojets are also classified according to the type of compressor used. Earlier models invariably used a compressor similar to the centrifugal pump of the
turbo supercharger and were called centrifugal flow engines. Because considerable energy was expended to change the direction of airflow as it was being com- pressed, the centrifugal pump was later replaced by a device similar to a turbine wheel in the turbo super- charger. This engine was called axial flow and per- mitted air to flow in more of a straight line during its compression.
Regardless of type or manufacturer, turbojet en- gines consist, primarily, of four sections. These sec- tions are: (1) compression, (2) combustion, (3) tur- bine, and (4) exhaust. The turbine lies directly behind the combustion section, and is driven by the gases leaving the combustion chamber. The shaft, which the turbine turns, also supports the compressor which compresses the incoming air before it enters the com- bustion chambers. Fuel is injected into the combus- tion section by a spray nozzle and burned. Ignition is continuous, and spark plugs or ignitors are required
Figure 62 — Gas Generator Section of a Turbofon Engine
48 FUNDAMENTALS OF AVIATION AND SPACE TECHNOLOGY
only for starting the engine. After the heated gas passes the turbine section, it flows through the ex- haust cone to the atmosphere, increasing in velocity and decreasing in pressure until it leaves the cone. In addition to the basic units of the turbojet engine, numerous appliances and accessories are required. These include fuel pumps, pressure regulators, oil pressure and scavenger pumps, a starter, a generator, and an ignition system. Some accessories have a more demanding job to perform than their reciprocating engine counterparts; e.g., fuel pumps (there are usu- ally two per engine ) must be able to develop pressure twenty to fift\' times that of the normal fuel pump of a reciprocating engine. The pressure regulators must be able to control fuel flow in widely varying condi- tions of atmospheric temperature and pressure. The starter must be able to accelerate the compressor, turbine and shaft from zero to 2000 or 3000 rpm in a very few seconds. The electric starter requires about 1,200 amperes of current during this period; however, larger jet engines often use a small gas turbine engine as a starter. There may also be other minor accessories, such as vacuum pumps, electric motors to move con- trollable vanes in the inlet or exhaust sections, etc.
COMPRESSORS
The first turbojets used centrifugal-flow compres- sors. (Figure 63.) The centrifugal-flow compressor is
easy to build and maintain, but rather inefficient be- cause the airflow direction is changed so often during its passage through the engine; e.g., this compressor is usually double sided, and consequently the air entering the rear inlet must traverse a complete circle before it enters the combustion chamber. The maxi- mum compression ratio obtainable with centrifugal- flow compressors is only about 3 to 1.
More recently developed turbojets, and almost all of the turboprop engines, use an axial-flow com- pressor. ( Figure 64. ) This compressor has several rows of compressor blades set into a rotating drum and separated by rows of somewhat similar blades in a fixed outer case called stators. The rotating blades (actually airfoils) force the air toward the rear with the stators serving as guide vanes to direct the air to the next row of blades. An engine with twelve rows of rotating blades has thirteen rows of stators and is called a twelve-stage compressor. The entire compres- sor is driven by one turbine wheel. This type of com- pressor can compress incoming air by as much as a 5 to 1 ratio. When higher compression ratios are desired, a split compressor, consisting of two different com- pressor sections, each with a row of rotors on its shaft, and separate turbines on the opposite ends of the shafts, may be used. Sometimes two or more stages of turbines are used to drive the compressor in the high compression section. Split compressors can achieve compression ratios as high as 12 to 1.
Figure 63 — Cutaway View of a Centrifugol Flow Compressor Eng
THE AIRCRAFT ENGINE 49
COMBUSTION CHAMBERS
Only a small part of the compressed air mixes with fuel and burns as it travels through the engine, al- though all of it is heated. A cannular combustion chamber has an inner and an outer liner, and as air leaves the compression section some flows between these liners while the rest enters the inner chamber where it mixes with fuel supplied by the fuel nozzle in the front of this chamber. The spray is controlled in such a way that the burning is concentrated near the center of the inner liner in order to prevent the burning of the metal. Thus, a layer of air separates the burning mixture from the inner liner. Since com- bustion chambers are connected by cross-ignition tubes, only two igniters are needed and then only for starting. As many as twelve to fourteen combustion chambers may be used in the average turbojet engine.
TURBINES
Turbine assemblies are quite similar in design and construction. The most critical stresses occur in this section because turbine blades or buckets must withstand high temperatures (sometimes as high as 1500° F. ) and centrifugal forces. Clearances ate very critical, and, because of expansion at high tempera- tures, will vary with the change in temperature. Cool- ing the turbine wheel and lubricating the bearings are major problems. The first is usually solved by ducting air from the compressor section to the turbine, and the second by using a special type of lubricant.
The biggest di£Ference between turbojet and turbo- prop engines (aside from the additional propeller and gear box in the turboprop) is in the turbine section. One turbine wheel, with its outer rim of buckets, is normally sufficient to drive several rows of compressor blades. However, if the main shaft must also turn a propeller, more rows of turbines are needed. Whether one or more turbines are used, a row of stationary blades is placed in front of each turbine to direct the gas flow toward the buckets at the correct angle. This particular row of stator blades is called a nozzle diaphragm.
EXHAUST CONES
The efficiency of a turbojet is increased by properly controlling the hot exhaust gases. The exhaust cone or nozzle may be convergent, divergent, or both, although the increased velocity of the convergent type is de- sired. Some engines use a variable cone which can be changed to get maximum efficiency. A thrust aug- menter, called an afterburner, is often used in military turbo jets. In effect, the afterburner becomes a ram jet engine which receives the compressed gas at its
Figure 64 — Axial Flow Compressor of Turbojet Power Unit
inlet and into which fuel is then discharged. Such a combination is often called a turboramjet. Since the gas is already aflame as it enters the afterburner, it continues to burn and the exhaust velocity is thereby greatly increased with only a slight increase in over-all engine weight. Fuel consumption is somewhat in- creased in proportion to thrust gained, but the increase in thrust per pound of weight, including both engine and fuel, is more than sufficient to warrant use of the afterburner when maximum performance is required.
THRUST VERSUS POWER
It is possible to calculate the power which a re- ciprocating engine will develop when its piston dis- placement, rpm, and mean eflFective pressures are known, and to test this calculation with a Prony brake. For a jet engine, however, only thrust can be ascertained until the forward speed factor is added. Since work is defined as force times dis- tance (W = FxD) and power is work per unit of time,
force X distance.
then power = -.
time
A jet engine developing 5,000 pounds of thrust tends to push itself, and the aircraft in which it is mounted, forward with that thrust. However, if the airplane is not moving, the force of 5,000 pounds multiplied by a distance of zero gives a product of zero foot-pounds of work and zero power. The same thrust, while pushing the airplane forward at a speed of 240 miles per hour (or 352 feet per second) is performing work at the rate of 5,000 x 352 X 60 foot- pounds per minute. Dividing this by 33,000, the num-
50 FUNDAMENTALS OF AVIATION AND SPACE TECHNOLOGY
ber of foot-pounds per minute required for one horse- power, gives 3200 horsepower. The same thrust at a higher speed means more power. Thus at a speed of 375 mph., the amount of horsepower developed by a jet engine is numerically equivalent to its thrust. For example a 5000 pound thrust engine develops 5000 H.P. at 375 mph. since
5000 X 375 X 5280
60 X 33,000 = ^°^^-
TURBOJET, TURBOPROP, AND TURBOFAN ENGINES
The low efficiency of a turbojet engine at low altitudes and low speeds is a major deterrent to its use for other than long range aircraft. As a com- promise between the turbojet and the reciprocating engine— propeller combination, the turboprop engine was developed. In the turboprop engine, a major part of the energy in the gases emerging from the combustion chambers is tranformed into mechan- ical energy in the rotating shaft. A propeller is con- nected to the shaft by reduction gears, so most of the tlirust developed by the turbine engine is utilized through the propeller. A considerable increase in efficiency at low altitudes and low speeds is thus obtained through the use of the turboprop. How- ever, a possible shortcoming still exists with the use of the propeller— that of poor efficiency when its rotational speed is too great. Most of the more power- ful reciprocating engines use propeller reduction gears to prevent the prop tip speeds from becoming super- sonic, at which point the developing shock waves cause loss of propeller efficiency.
The turbofan engine is a modification of the stand- ard turbojet engine. It can produce more thrust by expelhng a greater volume and weight of cooler gas. Through its large intake the turbofan pulls in four times as much air as the standard turbine engine. This gives a greater volume of gases expelled at lower velocity and temperature, thus producing in- creased thrust at a lower noise level. The turbofan engine has one or more rows of compressor blades extended several inches beyond their normal length to direct air back through an area which surrounds the regular engine giving what is called a forivard-
COMBUSTION CHAMBER
Figur* 65 — Rocket Power Unit
fan engine. The fan acts quite similar to an ordinary propeller. An alternative procedure is to extend one or more of the rows of turbine blades, resulting in an aft-fan engine. With a fan, there is a sufficient increase in thrust and efficiency to propel an airplane faster than the speed of sound without using an afterburner.
A more recent development, one which engineers are expecting to utilize in the engines of supersonic airliners designed to travel at speeds of Mach 3 or above, is the fan burner. Similar in operation to the afterburner of the normal turbojet engine, the fan burner engine obtains additional thrust by burning additional fuel in the fan duct. Thrust can be doubled with a fan burner, and in addition, these engines have lower operating temperatures, a wider range of available power, and a much lower weight per horse- power. In fact, the fan burner engine has proved to be very efficient and economical at low altitudes and speed without burning in the fan stream, and at high altitudes and speeds with burning in the fan stream. The high-thrust turboramjet has apparently been far surpassed in thrust as well as economy by the fan burner engine. ROCKET PROPULSION
Recent military successes in the field of rocket pro- pulsion have raised hopes and predictions of ex- tremely rapid intercontinental travel, and even inter- planetary travel. While it is true that rockets can be and have been developed which can deliver tremen- dous thrust, there are still many unsolved problems delaying wide acceptance of this method of propulsion for anything other than military projectiles. This does not rule out the use of rockets as auxiliary power for takeoff or emergency purposes for some manned air- craft, and for satellites of the earth, sun, moon, or some other planetary body. ( See Chapter 12. )
A major problem at present is fuel consumption. Whether the fuel be liquid or solid, rockets must still carry their own oxygen supply, thereby increasing fuel load weight and decreasing pay load weight. Rocket power is successful when the vehicle it powers can attain very high speeds and high altitudes. Both of these conditions have physiological implications which are serious.
Another difficult problem involves control of a rocket-powered aircraft while in flight. If the flight is made at sufficient altitude to warrant use of rocket propulsion, aerodynamic controls will be almost use- less. If the rocket leaves the low heavier layer of atmosphere and progresses to a high speed in the thin upper layer, the re-entry into the lower altitudes with its resultant friction and heat also causes trouble.
THE AIRCRAFT ENGINE 51
The military implications of rocket propulsion are awesome and frightening, particularly when coupled with electronics s\'stems which permit remote or automatic contiol of various "stages" of the composite rocket, and with intricate and remarkably accurate guidance systems. A schematic drawing of the essen- tial parts of a rocket appears in figure 65.
ATOMIC PROPULSION
The success of the atomic-powered submarine has led to a clamor for an airplane powered by an atomic engine; in fact, the Hight of such a plane by another government has been reported. Although the report may be premature, the possibility of such an engine cannot be denied. Basically, the engine would develop thrust using the same principle as the jet, with the atomic reactor providing the heat normally obtained in the combustion chambers of the conventional jet. Major problems, including lack of protection from radiation of the atomic materials, have delayed devel- opment of this engine. Quite possibly, its principal application may be that of an auxiliary engine— to be used only when the airplane has reached high speed and altitude by use of another type engine. Inter- planetary travel may become a reality if and when the atomic engine is perfected.
Summary
Early powerplants were unsuitable for aircraft be- cause they were heavy, cumbersome, and unable to
deliver sufficient horsepower. First aircraft engines were crude and inefficient, but had the same operating principle of present-day reciprocating engines.
To be satisfactory for aircraft use, an engine must be powerful, compact, and light in weight. Fuel and oil consumption must be within reason, and main- tenance must be relatively easy.
Almost all current reciprocating aircraft engines are air-cooled and either of the radial or horizontally- opposed type.
Practically all aircraft engines operate on the four- stroke cycle principle. There are five events in each cycle: intake, compression, ignition, power and exhaust.
The main functions of the lubrication system are to (1) lubricate, or reduce friction, (2) cool the engine, and (3) give a better seal between piston rings and the cylinder wall.
The carburetor acts as a control and mixing cham- ber for liquid gasoline and air. Gasoline is atomized and vaporized in the induction pipes and cylinders. The fuel charge is ignited at the proper instant by a spark plug which receives high voltage current from the magneto via the distributor and ignition leads.
Reaction engines, such as the ram jet, pulse jet, turbojet, turboprop, and rocket devices, produce thrust by expelhng gases through a jet or nozzle. Jet engines use oxygen from the earth's atmosphere but rockets carry their own oxygen, enabling them to produce thrust outside the atmosphere.
Questions
1. Why are the most liigh-powered reciprocating engines of the multi-row radial type?
2. Name the five events in a complete cycle in a four-stroke cycle engine.
3. How many power strokes should be delivered per minute by a nine-cylinder engine operating at 2200 R. P. M.?
4. What is to be substituted for each of the letters, P, L, A, and N in the horsepower formula? What does the 33,000 in the denominator represent?
5. What is the function of a carburetor in a recip- rocating engine? How is carburetor icing elim- inated or prevented?
6. What are the two main functions of the lubrica- tion system?
7. What causes high-voltage current to be induced in the secondary circuit of a magneto?
8. Under what operating conditions is a super- charger required? Why?
9. Name four different kinds of jet engines.
10. What is an afterburner, and what is its purpose?
11. What advantages does a turboprop engine have over a turbojet engine?
12. What is the purpose of the turbine in a turbo- jet? In a prop jet?
Why is a spht compressor used in high perform- ance jet engines?
Why is the turbofan engine superior to other types of jet engines?
Where is the "fan" located in the turbofan engine?
13.
14.
15.
UNIVERSITY Oh lUINOIS LIBRARV
Chapter 6 Airplane Instruments
Due to the inability of the human senses to cope completely with variable climatic conditions and com- plicated mechanical devices, it is essential that certain physical characteristics of the airplane be measured and indicated. These measured indications must be extremely accurate and readily accessible to the pilot. Safe, economical, and reliable operation of modern aircraft and their powerplants is absolutely dependent upon the proper use of instrmnents.
Instruments are divided into three classes: (1) flight instruments; (2) navigation instruments; and (3) en- gine instruments. The number of instruments found in various aircraft depends upon the size of the aircraft, and upon the purpose for which the aircraft is used. Multi-engine aircraft, for example, require a separate set of instruments for each engine and often require a duplicate set of instruments for the second pilot or the flight engineer.
In addition, the wide variety of aircraft operational temperatures, pressures, and speeds make it necessary to paint operational markings in various colors on the cover glasses or faces of the instnnnents. Short radial lines and arcs of circles indicate the safe operating limits prescribed by the manufacturer for a particular engine or aircraft.
The Federal Aviation Agency (FAA) also has re- quirements that must be met for certain conditions of flight operation, e.g., visual flight rules (VFR), instrument flight rules (IFR), and day and night op- eration. These FAA requirements also govern the number and kind of instruments to be found in a specific airplane.
Some of the more important instruments found in airplane cockpits are the airspeed indicator, altimeter, rate of climb indicator, compass, tachometer, oil pres- sure gage, oil temperature gage, turn and bank indi- cator, directional gyro, and gyro horizon. Before describing their operation and functions, it is neces- sary to discuss two other fundamental aircraft acces- sories which are part of the instrument system, i.e., the pitot-static tube and the venturi tube.
Pitot-Static Tube
The airplane's pitot-static tube (Figure 66) fur- nishes accurate measurements of (1) impact (pitot) and (2) static pressures. The pitot-static tube is com- posed of two separate tubes of seamless brass tubing mounted together in a housing or head. Specifically, the pitot-static tube is used to supply impact pressure to the sensitive element in the airspeed indicator and to maintain static pressure inside the housing of the aii-speed indicator, altimeter, and rate of climb instru- ment. The pitot-static tube is positioned on the air- plane so that its axis is parallel to the longitudinal axis of the airplane. It is attached to the airplane in a location that is away from the propeller's slipstream and in undisturbed air.
The pitot tube is open on the front so that it is sub- jected to the full impact of the air pressure which is created by the forward motion of the airplane. The static tube, however, is closed on the front end with holes drilled into its sides, top, and bottom in order to subject it to the pressure of the static or still air.
The pitot and static pressures obtained from these tubes are transmitted to the cockpit instruments by air-tight tubing. The instrument connection points for this tubing are always marked with "P" for pitot pres- sure and "S" for static pressure, to make easy, sure
lube solder cone -
Tube nu+ -'
Solder cone nut - '
nXDOD
Figure 64 — Standard PitolStolic Tube. 1. Solder Cone Nut; Nut; 3. Tube Solder Cone.
AIRPLANE INSTRUMENTS 53
Figure 67 — Venturl Tube
mechanical connections. Water, snow, ice, or other foreign matter which enters the pitot tube results in either restriction or complete stoppage of the air flow. Stoppage, of course, causes either inaccurate readings or complete operational failure of the airspeed indi- cator instrument.
Venturi Tube
The airplane's ventiu-i tube (Figure 67) develops suction or lower than normal atmospheric sea-level pressure. This suction operates vacuum-driven instru- ments on those aircraft which do not have engine- driven vacuum pumps.
Although the hollow venturi tube flares out on both ends, it has a restriction in the "throat" of the tube. When air passes through the throat of the tube, the velocity of the air increases, thereby causing a de- crease in the air pressure. A tube connected to this restiicted portion of the venturi then develops a pres- sure which is lower than the normal atmospheric sea- level pressure. A four-inch venturi, for example, causes a three-pound-per-square-inch drop in pressure, i.e., to 11.7 psi. Vacuum or suction is measured by an instru- ment which is calibrated in inches of mercury. Each inch of mercury weighs .49 lbs. per inch.
Venturi tubes, like pitot tubes, are mounted outside the airplane and freeze or restrict when subjected to ice and snow; therefore, an engine-driven vacuum pump is usually considered more dependable.
The Airspeed Indicator
The airspeed indicator is a flight instrument which aids in ( 1 ) determining the best climbing and gliding angles, (2) selecting the most satisfactory power set- tings for efficient flying speeds, and (3) maintaining
200 V
Figure 68 — The Pilot-Static Tube Showing the Connections to the Air- speed Indicator
the speed of the airplane within its safe operating limits.
The aiispeed indicator is composed of an air-tight case and a sensitive diaphragm capsule. The air-tight case is connected to the static tube, which keeps it at existing atmospheric pressure at all times. The dia- phragm capsule is connected to the pitot tube. As the airplane moves through the air, the pitot pressure causes the diaphragm to expand with an increase in speed and to contract with a decrease in speed. The difference between pitot pressures in the diaphragm and static pressures in the air-tight case operates a series of gears and levers which visually show the indicated airspeed (IAS), either in statute miles per hour or nautical miles (knots) per hour, on the face of the dial. ( Figure 68. )
The dial shows the indicated airspeed at which the airplane is moving through the air. This indicated airspeed is always different from true ground speed,
54 FUNDAMENTALS OF AVIATION AND SPACE TECHNOLOGY
except in still air at noniial sea-level atmospheric pressure. The pilot, however, is always able to calcu- late his ground speed from his indicated airspeed if he knows both the altitude at which he is flying, the temperature at that altitude, and the direction and speed of the wind. As the airplane gains altitude, the air becomes less dense and creates a lower atmos- pheric pressure. This lower atmospheric pressure af- fects the accuracy of the airspeed instrument, thereby necessitating the use of a correction factor to recalcu- late the true airspeed (TAS)— 2 per cent for each 1000 feet of altitude, i.e., for each 1000 feet of altitude, the airplane actually travels 2 per cent faster than the airspeed indicator reads. For example, at 5000 feet of altitude the airspeed indicator reads 150 mph. Apply- ing the correction factor:
TAS = 150 mph + (2% X 5000 ft. x 150 mph)
TAS = 150 mph -h (.02 X 5 X 150)
TAS = 150 mph + 15 mph
TAS = 165 mph It must also be borne in mind that if an airplane is flying at 100 mph. True Indicated Air Speed (TIAS) into a 20-mph headwind, the actual speed with respect to the ground (GS) would be only 80 mph. (See definition of Calibrated Air Speed in Appendix.)
The reliability of the airspeed indicator is de- pendent upon ( 1 ) the pressures delivered to the air- speed indicator's mechanism by the pitot-static tube, and (2) the accurate response of this mechanism to the pitot-static tube pressures.
The Altimeter
The altimeter, a flight instrument, has two specific fimctions:
1. To measine the elevation of the aircraft above any given point on the ground regardless of that point's elevation above sea level. This altitude meas- urement method is called the "Field Elevation Pres- sure" system and represents the field elevation baro- metric pressure at a point which is 10 feet above the average elevation of the airport's runways.
2. To measure the altitude of the airplane above sea level. This altitude measurement method is called the "Altimeter Setting" system and represents atmos- pheric pressure, in inches of mercury, at normal sea- level pressures. Thus, the altimeter— an aneroid barom- eter—(Figure 69) is a sensitive instrument, calibrated in feet of altitude instead of inches of mercury, which measures atmospheric pressure.
The aneroid is either a sealed diaphragm capsule or a metal cell enclosed in an airtight case which is con- nected to the static tube. Atmospheric pressures from
the static tube act on the capsule by either compress- ing or expanding the diaphragm. The movements of the diaphragm are then transferred, through a system of levers and gears, to indicating hands on the face of the altimeter. As the airplane's altitude increases, atmospheric pressure decreases and allows the sealed diaphragm to expand. The amount of expansion con- trols the hands on the face of the altimeter. As the airplane descends, however, the increase in atmos- pheric pressure causes the diaphragm to contract and indicates a decrease in altitude. Atmospheric pressures
Figure 69 — Altimeter
constantly change and whenever a change in pressures occurs the altimeter hands move— even when the air- plane is in a stationary position on the ground.
Because of the changing barometric pressure, the altimeter fails to indicate the correct height unless other means are provided to keep it accurate, such as a knob on the front of the instrument. If a pilot, flying locally, wants to know his height above that particular airport, he sets the dial hands, before takeoff, to read "zero." After takeoff, the altimeter indicates his alti- tude only above that airport. The above description is an example of how the Field Elevation Pressure sys- tem is used to indicate altitude.
If a pilot is flying cross-country, he uses the Altim- eter Setting system because he must know his specific height above sea level. All map elevations are given in terms of height above sea level. Prior to takeoff the pilot will set his altimeter, by means of the knob, at the surveyed elevation of his departure airport rather than on zero. On this setting the reading on the barometric scale will be the local pressure corrected to sea level barometric pressure. After takeoff, the altimeter indicates the airplane's altitude above sea level rather than the altitude above the surveyed airport's elevation.
AIRPLANE INSTRUMENTS 55
Rate of Climb Indicator
The rate of climb indicator, a flight instrument, is also called a vertical sp>eed indicator and is used to show either a gain or a loss of altitude regardless of the atitude of the aircraft. Specifically, it is used ( 1 ) to show rate of ascent or descent, (2) to accomplish banked turns without gain or loss of altitude, and (3) to establish constant and definite rates of descent when making instrument landings.
The rate of climb instrument (Figure 70) also con- sists of a metal diaphragm enclosed in an airtight case. The diaphragm is connected to the static tube and the air-tight case is sealed except for a small, calibrated leak which leads to the internally-connected static line. The capsule— diaphragm— is subject to the ascend- ing and descending pressure changes. To measure this rate of change in atmospheric pressure, the dial hands indicate a rate of change in feet per minute. The static
Figure 70 — Vertical Speed Indicator
pressure inside the capsule or diaphragm changes faster than the air pressure inside the case because the small-size hole in the case permits a calibrated leak. Normally, when the airplane is neither ascending nor descending, the pressure both inside and outside the capsule is equal, and the instrument hand reads "zero." The face of the instnmient is marked both in a zero-to-2000-feet clockwise direction and a zero-to- 2000-feet counterclockwise direction. Each increment or marking represents 100 feet per minute. The unit pointer— hand— rotates from the zero mark in either a clockwise or counterclockwise direction. Normally, the instrument has a sector stop which limits the motion of the pointer, for either ascent or descent, to 1900 feet per minute. All rates of climb have an in- herent lag of six to nine seconds because of a built-in restriction which prevents instrument oversensitive- ness which might be caused by bumpy air.
The Magnetic Compass
The magnetic compass ( Figure 71 ) is a navigational instrument used to indicate the heading on which the airplane is flying. The magnetic compass consists of a metal bowl filled with a liquid and a numbered, magnetic card element which has attached to it a system of magnetized needles. This card and the mag- netized needles are suspended on a pivot and are always free to turn. The magnetized needles normally point toward magnetic north. The magnetized card is calibrated into a 360-degree circle. A reference line, called the lubber line, and the graduations of the card are always visible through a glass window on the front of the bowl.
Figure 71 — Mognetic Composs
The liquid inside the instrument— a mixture of kero- sene and mineral oil which will not freeze— dampens the oscillations of the card. There is also an expansion chamber built into the compass to provide for ex- pansion and contraction of the damping fluid— which would result from altitude and temperature changes. The magnetic compass also has permanent magnets located above the card, which compensate for com- pass deviations that are caused by radio, electrical equipment, and metal parts of the aiiplane. The com- pensating assembly, or magnets, may be rotated by adjusting screws which are marked N-S and E-W on the face of the magnetic compass.
The compass is mounted in the airplane so that the lubber line and the card pivot are aligned parallel to the longitudinal axis of the airplane. The magnetic compass is the only instrument in the airplane which indicates earth's magnetic north.
The magnetic compass, however, is subject to errors which must be taken into consideration "when estab- lishing a true heading." Variation is caused by the difference in the geographical location between the True North and the Magnetic North. Since the mag-
56 FUNDAMENTALS OF AVIATION AND SPACE TECHNOLOGY
netic compass always points to Magnetic North, magnetic variation is always indicated on aeronautical charts.
Errors in the magnetic compass can also be caused by acceleration, turning, and by bumpy or rough air since the card swings while it tries to keep itself aligned with Magnetic North.
Tachometers
The tachometer is an engine instrument and is used to measure the engine crankshaft speed in revolutions per minute (rpm).
On airplanes equipped with fixed pitch or adjust- able pitch propellers this instrument is of primary importance because engine speed is directly related to the power output of the engine. The tachometer responds instantly to any change in engine speed.
Some specific uses of the tachometer, when used on airplanes with fixed pitch propellers, are ( 1 ) to test the engine and magnetos prior to takeoff, (2) to aid the pilot in selecting the best jDOwer settings, (3) to indicate a loss in power, and (4) to indicate safe operating limits of the engine.
There are two types of tachometers used on modem airplanes : ( 1 ) magnetic tachometers, and ( 2 ) electric tachometers.
MAGNETIC TACHOMETER
The magnetic tachometer (Figure 72) derives its name from its internal mechanism. It is similar to and works on the same principle as an automobile speed- ometer except that it is calibrated in revolutions per minute (r^im) instead of miles per hour (mph). The magnetic tachometer is driven by a flexible shaft encased in a metal housing. On some of the smaller engines the flexible tachometer shaft is driven from an extended shaft on one of the oil pump gears located on the back of the engine. On other engines
a special tachometer drive is used which consists of a gear train meshing with an accessory gear on the back of the engine.
The mechanism of the tachometer consists of a ro- tating magnet, a round drum, and a hairspring. The rotating magnet is driven by the tachometer shaft through suitable couplings. The round drum or cup fits loosely over the rotating magnet and is fastened to a staff or shaft which is geared to the pointer shaft. The hairspring is attached to the shaft on the drum. When the rotating magnet is turned, the force or pull of the magnetic field pulls the drum against the force of the hairspring. When the force of the magnet equals the strength of the spring, the drum turns and rotates the pointer shaft by means of the gearing. The faster the rotating magnet turns, the more lines of magnetic force are applied to the drum, causing the pointer to move and thereby show an increase in rjim. The face of the instrument is calibrated in increments of 100 rpm.
Figure 72 — Mognetic Tachometer
Figu
73 — Electricol Tachometer
AIRPLANE INSTRUMENTS 57
ELECTRIC TACHOMETER
The electric tachometer (Figure 73) consists of two units: the indicator, which is mounted on the instrument panel, and the generator, which is attached to the tachometer drive of the engine. The two units are connected by means of an insulated electrical cable. Because this instrument needs no flexible ta- chometer shaft to drive its mechanism, it is readily adaptable to multi-engine installations and to those aircraft where the distance from the engine to the in- strument panel is excessive. The electric tachometer is actually a voltmeter, but calibrated in revolutions per minute instead of in volts. The mechanism, contained in the indicator unit, is a permanent magnet with a moving coil connected to a pointer. The moving coil moves within the air gap of the permanent magnet. The pointer and coil movement are dampened by a hairspring and are mounted in jewelled bearings which permit steady and accurate readings. The elec- trical output of the tachometer generator is routed through a coil in the indicator unit. As engine speed increases the tachometer generator increases its energ\ output. This increased voltage feeds into the moving coil of the indicator unit and causes the coil to move against the restraining hairspring, thereby indicating an increase in rpm. A decrease in engine speed results in a decreased voltage output of the tachometer generator and the hairspring is then able to overcome the attraction between the coil and the permanent magnet, thereby causing the pointer to move toward the lower end of the scale.
Oil Pressure Gage
The oil pressure gage (Figure 74) is an engine in- strument required on all airplanes. It shows the pres- sure at which the lubricant is being forced into the bearings and to the other points of the lubricating system. Among the uses of the oil pressure gage are (1) a warning of an impending engine failure if the oil pump fails or oil lines break, and (2) visual indi-
Figure 74 — Oil Pressure Gage
Figure 75 — Bourdon Tube
cation that oil is circulating under proper pressure before takeoff.
The oil pressure gage is calibrated in pounds per square inch (psi). The instrument contains a Bourdon tube mechanism (Figure 75) which is used in almost all fluid pressure gages. A Bourdon tube is a hollow ciu-ved tube made of spring-tempered brass or bronze and has an elliptical cross-section. It is sealed at its outer end. The outer end of the tube is free to move, while the other end is rigidly fastened to the instnr- ment case. The outer or free end of the tube is at- tached to a lever and gear segment which actuates the pointer. The stationary end of the tube has an opening connected to a fitting on the back of the instrument case. The fitting has a restriction to prevent surging and oscillation of the pointer. An oil line from a high pressure passage in the engine connects to the restricted fitting on the back of the instrument case. When the engine is started, some pressure should be indicated on the oil pressure gage almost immediately. If no pressure is indicated after thirty seconds of oper- ation, the engine should be shut off and the cause for operational failure investigated so as to prevent dam- age to the engine.
Oil Temperature Gage
The oil temperature gage ( Figure 76 ) is an engine instiument used on all aircraft. The Federal Aviation Agency requires a suitable means for taking the oil temperature as it enters the engine. This FAA require- ment is important since oil plays a big part in the cooling of aircraft engines.
The oil temperature gage is used ( 1 ) to enable the pilot to operate the engine within safe operating tem- peratures, and (2) to warn the pilot of engine over- heating. The oil temperature gage used on most aircraft is a vapor pressure type thermometer and is calibrated in degrees of Fahrenheit or Centrigrade.
58 FUNDAMENTALS OF AVIATION AND SPACE TECHNOLOGY
Figure 76— Oil Te
alure Gag
A vapor pressure thermometer consists of tliree units: the indicator unit, which is mounted in the in- strument panel; the bulb, which is located at the point of temperature measurement; and the capillary tube, which connects the indicator to the bulb.
The indicator unit contains a Bourdon tube mecha- nism similar to the oil pressure gage except that the Bourdon tube also has a progressive restrainer to per- mit the use of a uniformly graduated scale. The pro- gressive restrainer is necessary because vapor pressure does not increase uniformly with temperature. The bulb is a hollow brass cylinder about three inches long and one-half inch in diameter. It contains a volatile liquid, meth\l chloride, which actuates the instrument or indicator unit.
The capillary tube is a very small annealed copper tube protected with either a shield of braided wire or a helical wound tube. The capillary tube connects the bulb and the indicator unit and is used to transmit the vapor pressure from the bulb to the opening in the Bourdon tube.
The operation of the vapor pressure thermometer is entiiely automatic. As the temperature of the bulb increases, the liquid methyl chloride, being very volatile, changes to a gas. This change causes an in- crease in pressure which is transmitted through the capillary tube to the Bourdon tube. The Bourdon tube tends to straighten out and its movement is transmitted through the linkage to the pointer on the face of the gage.
The three units of a vapor pressure thermometer are integrated and cannot be taken apart without losing the gas and thereby rendering the instrument useless. For this reason care must be taken to prevent cutting, denting, or stretching the capillaiy tube.
Turn and Bank Indicator
The turn and bank indicator (Figure 77) is a flight instrument which is actually a combination of two instruments. It combines an inclinometer— a pendulous
device— and a rate of turn indicator— a gyroscopic de- pigu
Figure 77 — Turn and Bonk Indicator
vice. It is becoming a widely-used flight instrument, especially under conditions of jioor visibility.
The turn and bank indicator enables the pilot ( 1 ) to maintain straight and laterally level flight, (2) to make precision turns at pretermined rates, and (3) to coordinate rudder and ailerons when making banked timis. It may be either a vacuum-operated instrument or an electrically-driven instrument. Both types operate in the same manner and on the same general principles.
The turn indicator portion indicates motion about the vertical axis of the airplane and measures the rate of this motion. It is composed of a suction or vacuum- driven gyro rotor located in the rear of the instrument case, a restraining spring, a dashpot for damping, and an indicator needle or hand to indicate the rate of turn. The dial is marked with the letters "L" and "R" and also has a neutral position with an index mark on each side. The index marks indicate a timed one- minute turn of 360° when the needle coincides with the index. The turn indicator operates on the gyro- scopic principle of precession. Due to the rigidity of
AIRPLANE INSTRUMENTS 59
Left turn ~ Left turn
Skidding out. not enough bonk Slipping in, too muctibank
Figure 79 — Visual Indications of Various Turn and Bank Conditions
a spinning gyro, it tends to precess at right angles to an applied torque. The gyro rotor is mounted so that it turns about the lateral axis of the airplane. When mounted in this manner, the gyro responds only to motion about the vertical axis of the airplane.
If the airplane turns to the left, (Figure 78) the gyro assembly rotates as indicated by the arrow "b." The immediate reaction of the gyro to this turning force is a rotation "c" about the "X" axis until "Z" has aligned itself with the original position of "Y." This is the natural reaction of a gyro mounted in this manner and is called precession.
The precession of the gyro, or its reaction to the applied torque, acts against the force of a restraining spring and is limited by stops to a movement of about 45 degrees from each side of the vertical. The spring serves to balance the gyroscopic reaction or precession during a turn and to return the assembly to its neutral or vertical position as soon as the airplane assumes a straight flight pattern. The action of the gyro assembly is damped by the dashpot and when properly adjusted the displacement of the gyro and the needle is directly proportional to the rate of turn of the airj^jlane. When centered, the needle shows that the airplane is flying straight, disregarding drift, pitch, and bank. When the needle is off center it indicates that the airplane is turning in the direction shown by the needle. Figure 79 shows indicator readings for several different con- ditions.
The bank indicator portion of the instrument con- sists of a black glass ball inside a curved glass tube. The glass tube contains a nonfreezing liquid which serves as a damping fluid. The bank indicator or in- clinometer is located in the front of the instrument case and is visible through the instrument's glass cover.
The action of the bank indicator can be compared to a pendulum which is acted upon by centrifugal
force. It shows motion about the longitudinal axis of the airplane. When the airplane is making a perfectly banked turn, the ball, due to centrifugal force, remains in the center of the glass. The correct bank is always indicated for any tiu-n, but no indication is ever given of the amount of bank. In straight flight or in a turn, the centered ball indicates proper lateral attitude of the airplane. If the ball moves in the direction of the turn, it indicates that the airplane is slipping, i.e., the angle of bank is too steep. If the ball moves in a direction opposite to the turn, it indicates that the airplane is skidding toward the outside of the turn, i.e., the airplane is not banked enough.
The indications of these two instruments combined in one dial always show the rate of turn and the lateral attitude of the airplane during straight flight or during turns.
The Directional Gyro
The directional gyro is a navigational instrument sometimes called a gyro compass or a turn indicator. This instrument establishes a fixed reference point to assist the pilot in maintaining flight direction. Unlike a magnetic compass the directional gyro has no direc- tive force to return it to a fixed heading. It must be checked occasionally and, if necessary, reset by a caging knob.
The directional gyro (1) supplements the compass in keeping "on course," (2) shows the amount of turn, (3) maintains alignment when making instrument landings, and (4) aids in locating radio beacon sta- tions. (Figure 80.) It is a horizontal, axis-free compass provided with an azimuth card and a setting device. The instrument, itself, is vacuum operated by suction from the engine-driven vacuum pump or the venturi tube.
The spinning gyro rotor is mounted horizontally and is supported in a gimbal ring which is free to turn about an axis on bearings in the vertical ring. The ver-
Figure 80 — Directional Gyro
60 FUNDAMENTALS OF AVIATION AND SPACE TECHNOLOGY
tical ling is mounted in bearings and is free to turn about the vertical axis. The circular azimuth card visi- ble through the instrument cover glass is graduated in degrees and is attached to the vertical ring. A caging knob in the front of the instiimient is used to set the card on a desired heading and to cage the gyro. When the knob is pushed in, it engages a pinion gear to a gear attached to the gimbal ring. By turning the knob, when it is thus engaged, the gimbal ring, vertical ring, and azimuth card can be rotated to any desired head- ing. The rotor, spinning at appro.ximately 12,000 rpm, obeys a gyroscopic principle of rigidity. Thus the rotor, gimbal ring, and the circular azimuth card remain fixed, the airplane moving around them.
When establishing a course, the pilot refers to the magnetic compass, then cages the gyro and selects a heading by use of the caging knob. After setting the card, the knob is pulled out, and the instrument is then in operation and will function properly until it is either upset or recaged.
Any bank in excess of 55 degrees will upset the gyro and cause the card to spin. The airplane must then be leveled, the gyro caged, and reset. The directional gyro will gradually drift off a heading over a period of time and should be reset at 15-minute intervals. Gyro drift should not exceed 5 degrees in 15 minutes on any single heading. Care should be taken in both setting the instrument and uncaging the gyro. The knob must always be pidled straight out with no turn- ing motion. If the knob is turned, even slightly, the card will begin to turn slowly and the instrinnent's natural tendency to drift off course will be speeded up.
The Gyro Horizon
The gyro horizon ( Figure 81 ) is a flight instrument often called an artificial horizon or an attitude gyro. By visually showing a miniature airplane and a gyro- actuated horizon, the pilot can look at the instrument and determine his flight attitude without reference to the ground.
The gyro horizon ( 1 ) enables the pilot to orient himself under conditions of poor visibility by provid- ing a reference in the form of an artificial horizon;
(2) shows the attitude of the air]^)lane's flight with reference to the real horizon and to the ground; and
(3) aids in maintaining the proper glide angle when making an instrument landing.
The gyro horizon is a vacuum-driven instrument which utilizes vacuum or suction from the vacuum pump or venturi tube as its source of power. The instnmient has a gyro rotor, which spins at approxi- mately 12,000 rpm, mounted in a case. The rotor is mounted so that its axle is vertical, thus allowing it
Figure 81 — Gyro Horizon
to spin in a horizontal plane. The case contains the rotor, on pivots, which is attached to a gimbal ring The horizon bar is attached to an arm pivoted at the rear of the gimbal ring and is controlled by the gyro tlirough a guide pin. This entire assembly is mounted on pivots located at the front and the back of the case. The dial is an integral part of the gimbal mount and follows the precession movement of the rotor. A minia- ture airplane image is located on the front of the instrument and is adjustable. The gyro horizon always indicates the attitude of the airplane in which the in- strument is mounted.
A caging knob is located on the front of the instru- ment to level the internal mechanism properly when it is upset. The limits of operation of the gyro horizon are 60 degrees of pitch and 90 degrees of bank. Any- time that these limits are exceeded, the mechanism will be upset and its readings will be erroneous.
The gyro horizon operates on the same fundamental gyroscopic principle as the directional gyro, i.e., rigidity. When the rotor is spinning, it will maintain itself in its plane of rotation unless upset. On the face of the instrument the position of the gyro rotor is indicated by the horizon bar, which is actuated by a pin protruding from the gyro case through a slot in the gimbal ring. Any tendency of the gyro to depart from its true position is corrected by a pendulous de- vice which constantly maintains the axle of the gyro in its vertical position.
The horizon bar remains stationary. Only the instru- ment case and the miniature airplane move when the airplane is banked,