What Makes Airplanes Fly?: History, Science, and Applications of Aerodynamics

225 Pages·1991·6.58 MB·English

by  Peter P. Wegener (auth.)

What Makes Airplanes Fly?
Peter P. Wegener
What Makes Airplanes Fly?
History, Science, and Applications of Aerodynamics
With 89 Illustrations
Springer-Verlag
New York Berlin Heidelberg London
Paris Tokyo Hong Kong Barcelona
Peter P. Wegener
Engineering and Applied Science
Yale University
New Haven, CT 06520, USA
Cover illustration: Otto Lilienthal in 1895 on a biplane glider. See page 17.
Wegener, Peter P., 1917-
What makes airplanes fly? : history, science, and applications of
aerodynamics / Peter P. Wegener.
p. cm.
Includes bibliographical references and index.
ISBN-13: 978-1-4684-0405-0
1. Aerodynamics. I. Title.
TL570.W4 1991
629.132'3-dc20 91-18396
Printed on acid-free paper.
© 1991 Springer-Verlag New York Inc.
Softcover reprint of the hardcover 1st edition 1991'
All rights reserved. This work may not be translated or copied in whole or in part without the writ
ten pennission of the publisher (Springer-Verlag New York, Inc., 175 Fifth Avenue, New York,
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The use of general descriptive names, trade names, trademarks, etc., in this publication, even if
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Typeset by Publishers Service of Montana, Bozeman, MT.
987654321
ISBN-13: 978-1-4684-0405-0 e-ISBN-13: 978-1-4684-0403-6
DOl: 10.1007/978-1-4684-0403-6
ToA.
Preface
This book is addressed to all who are interested in aerodynamics. In addition
to the aerodynamics of flight from low-speed craft to supersonic airliners, the
topic is interpreted in a broad sense, including the aerodynamics of automo
biles, bird flight, and the motion of diverse objects through air or water. The
fundamentals of basic mechanics and fluid mechanics - the physics underly
ing aerodynamics-and general remarks on the nature of science and engi
neering are interspersed in the text. The use of mathematics is minimal; it is
restricted to elementary algebra, and only a handful of simple but basic equa
tions appear. This is in harmony with the expectations of college students in
the humanities and social sciences taking courses outside their field and of
general readers whose interest in flight transcends the discussion of specific
airplanes, piloting, airlines, airports, and so on.
A brief history of man's attempts to fly from the early days to the Wright
brothers and beyond is given. The selection from the multitude of events over
the centuries is of necessity incomplete, but some of the major contribu
tions - in particular those that influenced the Wright brothers - are discussed.
An overview of the current status of aeronautics and some thoughts on the
future of air traffic are given at the end. These discussions are restricted to
civilian air transportation. Books on history, aeronautical engineering, and
military aviation are listed in Appendix 4 to facilitate further study.
The general reader may safely skip all appendixes and the footnotes. Even
the few equations can be dispensed with, since their meaning is explained in
the text. However, college students who use this book in general science or
engineering courses directed to liberal arts students will find it useful to hear
more about the metric system of measurement and subjects such as dimen
sional analysis. The latter is an important contribution of engineers to human
knowledge that gave us, for example, the Reynolds and Mach numbers. Care
ful study of this material will enable students to solve the problems found in
the study guide. The tables of properties in the book are sufficient to extract
the numerical values required for their solution.
I developed the material given here while teaching Yale College students in
the liberal arts, and I hope that the book may be used similarly elsewhere as
a textbook. The instructor ought to be an engineer or scientist with an interest
vii
in the fascinating topic of flight, who in addition believes in a liberal education
that cannot ignore science and engineering. About a century ago, man rose for
the first time from the surface of the earth in gliders and powered aircraft,
machines that must be counted among the greatest engineering feats. Who is
not curious to find out how it is possible for huge modem airliners to take off
at a steep angle and transport people and goods to any place on earth?
I first considered turning my rough lecture notes into a book in 1986, during
a term as a fellow of the Institute for Advanced Study in Berlin. The manu
script was written with the support of a grant to Yale University from the
Alfred P. Sloan Foundation. Sam Goldberg, who directed the foundation's
New Liberal Arts Program, suggested that I write this text. I am deeply grate
ful to him for his trust in and continuing support of this venture. My colleagues
W. Jack Cunningham and Katepalli R. Sreenivasan read the manuscript and
provided important advice.
John H. McMasters of the Boeing Commercial Airplane Company, Rein
hard Hilbig of Messerschmidt-BOlkow-Blohm, and Richard S. Shevell of
Stanford University provided much needed advice and data on aircraft aero
dynamics. Werner Nachtigall of the University of Kaiserslautern commented
on the biological aspects of bird flight. These colleagues extended valuable
aid, but all possible errors are of course my own responsibility. The physics
editorial department of Springer-Verlag New York read the manuscript and
provided many suggestions. I am grateful for this sensitive advice.
Finally, my gratitude goes to Stephen Mayer, who edited the manuscript.
His background is in the humanities, and when he was stumped, I knew I had
to make changes in the text. Susan Hochgraf prepared the drawings, and
Mafalda Stock expertly operated the word processor.
viii Preface
Contents
PREFACE .................................................. Vll
CHAPTER 1 A Dream Comes True: The Wright Brothers
and Their Predecessors ....................... .
1.1 The First Flights at Kitty Hawk. . . . . . . . . . . . 1
1.2 Mythology and Legend .................. 4
1.3 Early Adventures. . . . . . . . . . . . . . . . . . . . . . . 6
1.4 From Cayley to the Wright Brothers. . . . . . . . 10
CHAPTER 2 Milestones of the Modern Age .................. 25
2.1 Notes on Aeronautical Research. . . . . . . . . . . 25
2.2 Great Moments in Aviation. . . . . . . . . . . . . . . 27
CHAPTER 3 The Nature of Liquids and Gases. . . . . . . . . . . . . . . . 41
3.1 Description and Properties ............... 41
3.2 Behavior of Liquids at Rest. . . . . . . . . . . . . . . 43
CHAPTER 4 The Atmosphere of the Earth ................... 47
4.1 History and Composition. . . . . . . . . . . . . . . . . 47
4.2 Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.3 Global Circulation. . . . . . . . . . . . . . . . . . . . . . 54
CHAPTER 5 Air in Motion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
5.1 Description of Movement: Kinematics. . . . . . 57
5.2 Conservation of Mass and Energy. . . . . . . . . . 61
5.3 Viscosity and Turbulence. . . . . . . . . . . . . . . . . 68
5.4 The Boundary Layer .................... 74
CHAPTER 6 Thrning to Aerodynamics. . . . . . . . . . . . . . . . . . . . . . . 79
6.1 How Do We Test Models of Airplanes? ..... 79
6.2 Drag, Lift, and Other Coefficients ., . . . . . . . 85
CHAPTER 7 Aerodynamic Drag. . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
7.1 What is Drag? Blunt Bodies. . . . . . . . . . . . . . . 87
7.2 The Strange Case ofthe Sphere. . . . . . . . . . . . 90
7.3 Slender Bodies, Skin Friction, Airfoils. . . . . . 94
7.4 Automobiles, Etc., Etc. .................. 101
ix
CHAPTER 8 Aerodynamic Lift . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 109
8.1 Early Experience and Some History. . . . . . .. 109
8.2 Lift of the Infinitely Extended Wing. . . . . . .. 113
8.3 The Finite Wing of an Airplane. . . . . . . . . . .. 122
8.4 How Birds Fly and Why We Cannot
Copy Them. . . . . ... . . . . . . . . . . . . . . . . .. 123
CHAPTER 9 Notes on the Whole Airplane ................... 131
9.1 Stability and Control... . . . .. . . . . . . . ... .. 131
9.2 Propulsion: From Propellers to Rockets. . . .. 135
CHAPTER 10 Toward High Speed: Supersonic and
Hypersonic Flight. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 145
10.1 Pushing the Speed of Sound: Flight at M = I? 145
10.2 From Supersonic Transports to the Orient
Express ............................. 156
CHAPTER 11 Air Transportation and the Outlook for the Future.. 167
11.1 The New Traffic Patterns. . . . . . . . . . . . . . . .. 167
11.2 What Will the Future Bring? . . . . . . . . . . . . .. 174
ApPENDIX 1 Facts from Algebra . . . . . . . . . . . . . . . . . . . . . . . . . . .. 181
ApPENDIX 2 Model Testing and Similarity ................... 185
A2.1 Aircraft Nomenclature and Model Testing. .. 185
A2.2 Dimensions and Units ................... 187
A2.3 Similarity Parameters and Model Testing. . .. 189
ApPENDIX 3 History of the Metric System: The SI System
and Conversion Tables . . . . . . . . . . . . . . . . . . . . . . . .. 195
ApPENDIX 4 A Guide to Further Reading .................... 201
ApPENDIX 5 Study Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 207
FIGURE AND TABLE CREDITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 213
NAME INDEX. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 215
SUBJECT INDEX. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 219
x Contents
A Dream Comes True: CHAPTER
1
The Wright Brothers
and Their Predecessors
It is not extravagant to say that the 17th of
December 1903, when the Wright brothers made the
first free flight through the air in a power-driven
machine, marks the beginning of a new era in the
history of the world.
SIR WALTER RALEIGH (1861-1922)
1.1 The First Flights at Kitty Hawk
In the wind-swept sand dunes of Kill Devil Hills, about four miles south of Kitty
Hawk, North Carolina, on the Atlantic coast, an old dream of man became a
reality. By the toss of a coin on December 14, 1903, Wilbur Wright (1867-1912)
won the first turn at piloting the powered airplane he had built with his brother
Orville (1871-1948). The weather was beautiful, but the wind seemed insuffi
cient for the Wright Flyer I to start from the 90 slope of the dune. The two skids
of the aircraft-no undercarriage with wheels existed at the time-were set on
a yoke running on a single track. Five men from the local lifesaving station
helped with this work. The engine was warmed up while the flying machine was
restrained. When all was ready, the men holding it let go, and, after a short run
of 35 to 40 feet on the track, the airplane lifted off the yoke into the air. Despite
this initial success, the Flyers nose turned up too quickly, leading to a stall. A
rough landing in the sand broke one of the skids and damaged a control surface,
ending further attempts at flight for the day.
What had happened? Stall implies a loss of lift. This occurs if the angle of
an airplane with respect to the wind direction, the so-called angle of attack,
becomes too great. It is the aerodynamic lift force that opposes the weight of
a heavier-than-air flying machine to keep it aloft. The balance of forces in the
vertical direction is shown in the schematic diagram of Figure 1.1, which
depicts the fundamental idea of flight. The lift is largely produced by the wings
of the aircraft. In cruising flight illustrated in the figure -level flight at con
weight
stant speed - the lift is exactly equal to the weight of the airplane, and the two
forces compensate each other.
On December 17, repairs were completed, and the attempt to fly was
resumed. A brisk wind of about 27 miles per hour made the sloping track
unnecessary. The wooden rail was now put on smooth, level sand near the
building that housed the Wright brothers' workshop. It was a cold day, and the
work had to be interrupted by warm-up periods next to an improvised stove
Figure 1.1. The forces acting on an airplane in level
made of a carbide drum. Again the five witnesses were present. The Wright
flight at constant cruising speed. Lift and weight
brothers, ever methodical, wanted to make sure that their effort, if successful,
cancel each other, as do thrust and drag.
Figure 1.2. The first flight of a powered aircraft. The Wright brothers' Flyer I, with Orville at the controls and Wilbur at the right wing, covered 120 feet
in 12 seconds on December 17, 1903.
would be confirmed by independent observers. For years, attempts at flight
had been made. Would-be aviators in the United States and in other countries
had experimented with airplanes of reasonable or fantastic design. Unfounded
claims of success had appeared in several instances, yet no one had in fact
accomplished powered flight.
Orville Wright had positioned a camera on a tripod so that the airplane
would be in view of the lens when it reached the end of the wooden rail. One
of the local witnesses, John T. Daniels, was instructed to pull the string of the
shutter at the right moment. Now it was Orville's turn to pilot. Wilbur steadied
the right wing, the engine was revved up, and around 10:34 A.M. the Wright
Flyer llifted offthe rail into a 20-to 22-mph (9-to to-m/s) wind.* The aircraft
wobbled. Gusts of wind, marginal stability, and Orville's understandable inex
perience in piloting a powered aircraft combined to produce an erratic flight
path. A downward motion forced Orville to land 12 seconds later, after cover
ing a distance of 120 feet, less than the length of a modern airliner. Daniels
performed admirably with the camera, producing the famous picture shown in
Figure 1.2. Orville later calculated that the airspeed of the aircraft-that is, its
actual speed relative to the oncoming wind-was about 45 ft/s or 30 mph (14
mls or 50 lan/h). Had the air been calm, about 540 ft (165 m) would have been
*Por abbreviations and units, consult Appendix 3 and Tables A3.1-A3.2, which include conver
sion factors between the British and metric systems.
2 What Makes Airplanes Fly