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LEARNING TO FLY
IN THE
U. S. ARMY
_McGraw-Hill Book Co. Inc._
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[Illustration: A GROUP OF U.S. ARMY STUDENT AVIATORS.
_Frontispiece_
]
LEARNING TO FLY
IN THE
U. S. ARMY
A MANUAL OF AVIATION
PRACTICE
BY
E. N. FALES
FORMERLY ASSISTANT PROFESSOR OF MECHANICAL ENGINEERING
CHAIR OF AERONAUTICS, UNIVERSITY OF ILLINOIS
FIRST EDITION
SECOND IMPRESSION
McGRAW-HILL BOOK COMPANY, INC.
239 WEST 39TH STREET. NEW YORK
LONDON: HILL PUBLISHING CO., LTD.
6 & 8 BOUVERIE ST., E. C.
1917
COPYRIGHT, 1917, BY THE
MCGRAW-HILL BOOK COMPANY, INC.
THE MAPLE PRESS YORK PA
PREFACE
This book is primarily intended for non-technical readers; and for the
student aviators who, called from non-technical occupations, must cram
themselves at short notice with the gist of airplane flying; and who
must omit everything except the outstanding fundamentals.
The desired essentials are here given without sacrificing accuracy
to brevity. It has been necessary to omit many technical details of
interest to the aeronautical engineer, to whose needs other larger
textbooks are adapted as a complete survey of technical aeronautics. In
brief, the book presents the main principles of aviation, such as the
aviator must know in order properly to understand his airplane, keep
it trued up, and operate it in cross-country flights as well as at the
flying field.
Out of the 2000 aeronautical books now in existence, a few are adapted
to use as textbooks for the present need, but none give the particular
and abridged information in tabloid form such as must be adopted for
the best time economy of these students.
It is by the kind permission of Professor E. A. Holbrook, Mr. O. S.
Beyer, and Mr. C. M. Hebbert that chapters VI to XI have been included.
Acknowledgment and full credit is due them as co-authors. Chap. VI,
VII, and part of Chap. XI were prepared by Prof. E. A. Holbrook; Chap.
IX, X, pages 152-157 of Chap. VIII, and pages 173-177 of Chap. XI were
prepared by Mr. O. S. Beyer; Chap. VIII, pages 133-152, was prepared by
Mr. C. M. Hebbert.
In the Chapter on “History of Aviation” only those experiments are
treated which have a bearing on flight today; this chapter is to
be used in conjunction with the Chapter on “Principles of Flight,”
especially as regards controlling the airplane.
The question of Airplane Motors has not been touched, because to do
it justice would unduly increase the size of this volume, and because
adequate treatises on the subject are available.
_Dec._ 12th, 1917.
CONTENTS
PAGE
PREFACE vii
CHAPTER
I. History of Aviation 1
II. Types of Military Airplanes and Uses 18
III. Principles of Flight 39
IV. Flying the Airplane 80
V. Cross-country Flying 89
VI. The Rigging of Airplanes—Nomenclature 113
VII. Materials of Construction 120
VIII. Erecting Airplanes 133
IX. Truing up the Fuselage 158
X. Handling of Airplanes in the Field and at the Bases
Previous to and After Flights 166
XI. Inspection of Airplanes 173
LEARNING TO FLY
IN THE
U. S. ARMY
A MANUAL OF AVIATION
PRACTICE
CHAPTER I
HISTORY OF AVIATION
That part of the history of Aviation which has especial interest for
aviators is of recent date, and extends back only two dozen years. Of
course efforts have been made toward manflight ever since the early
sixteenth century, when Leonardo da Vinci invented the parachute and
became the first patron of aeronautics; between the time of this famous
artist and the present many experimenters have given their attention
to the problem, but previous to the last decade of the nineteenth
century nothing practical was achieved. Then, with the perfection of
the steam engine and the development of the gasoline engine, there came
inducement to sound experimentation, bringing forth such well-known
figures as Maxim, Langley, Lillienthal and Chanute.
The work of each of these men is an interesting story by itself,
especially that of Langley, who approached the matter from a strictly
scientific viewpoint, established testing apparatus and built
successful self-propelled steam models years before the Wright brothers
reported their independent successes. He reproduced his models to full
scale with every expectation of success, but failed, due to exhaustion
of his capital.
=Langley’s Experiments in Aerial Navigation.=—In all the history of
aerial navigation one of the most romantic stories is that describing
the scientific researches begun in 1887 by Langley and culminating in
1896 in the first really successful case of mechanical flight using a
prime mover; continuing up to 1903 when this first successful machine,
a model of 12-ft. span, was reproduced to full scale and manned for
its trial flight by a human pilot; and ending with the destruction of
this full-sized machine on launching, so that Langley missed the glory
of being the actual discoverer of manflight only by a hair’s breadth,
dying shortly afterward of a broken heart, as is conceded by those who
knew him. If this full-scale machine had performed as successfully in
1903 as it actually did after being rebuilt and partly remodelled a
decade later by the Curtiss company, Langley would have antedated the
first successful flight made by the Wright brothers by a narrow margin
of about 2 months.
[Illustration:
(_Courtesy S. S. McClure Co._)
FIG. 1.—The Langley steam model flying machine.
It flew a mile in 1896, the first successful airplane to fly with a
prime mover.]
=Lillienthal (Germany, 1894).=—But omitting details regarding the
early experimenters we will consider only that part of the history of
aviation most important to the prospective aviator. We will confine
ourselves to the sequence of gliding and power experiments begun by
Lillienthal, carried forward by Chanute and brought to completion by
the Wrights.
[Illustration:
(_Courtesy Jas. Means’ “Aeronautical Annual.”_)
FIG. 2.—Lillienthal’s biplane glider in flight, 1894.
Note.—(_a_) Arched wings; (_b_) fixed tail; (_c_) method of balancing
by swinging legs.]
[Illustration: (_Courtesy Jas. Means’ “Aeronautical Annual.”_)
FIG. 3.—Chanute’s biplane glider, 1896.
Note improvement in rigidity by bridge-type trussing.]
Lillienthal was the first man to accomplish successful flights
through the air by the use of artificial wing surfaces. After many
years of experiment and study of soaring birds he constructed rigid
wings which he held to his shoulders and which, after he had gained
considerable velocity by running forward downhill, would catch the air
and lift his weight completely off the ground. The wings were arched,
for he observed this was the case in all birds; flat wings proved
useless in flight, and suggested a reason for the failure of previous
experimenters. To these rigid wings Lillienthal fastened a rigid
tail; the wings and the tail comprised his “glider.” There were no
control levers and the only way the operator could steer was to shift
the balance by swinging his legs one way or the other. Lillienthal
constructed an artificial hill for his gliding so that he could coast
downward for some distance without striking the ground and he was able
to accomplish many glides of a couple of hundred yards in length.
=Chanute (Chicago, 1896).=—Chanute’s experiments in gliding were
quite similar to Lillienthal’s and were made on the sand dunes along
Lake Michigan outside of Chicago. His apparatus was more strongly
constructed, being of trussed biplane type, a construction suggested to
him by his experience in bridge building, and one which persists today
as the basis of strength in our present military biplanes.
=The Wright Brothers, 1901.=—Lillienthal was killed in a glide, having
lost control of his apparatus while some distance above the ground. The
Wright brothers read of his death and commenced thinking over the whole
problem. Lillienthal’s method of balancing his large apparatus by the
mere effect of swinging his legs appeared to them as a very inadequate
means of control. They came to the conclusion that the immediate
problem in artificial flight was the problem of stability, which they
felt should be solved by an entirely different means than that employed
by Lillienthal and Chanute. The work already done had demonstrated
without question that support in the air had been established; with
the addition of controllability the Wrights looked forward to doing
something worth while in the way of artificial flight.
To improve Lillienthal’s method of shifting the weight, they conceived
the idea of leaving the pilot in an immovable position in the glider,
and instead of obliging him to shift his weight this way and that, they
proposed to manipulate the surfaces of the wings themselves by means of
levers under the pilot’s control, so that the same result of balancing
could be obtained by quite a different and superior method.
They set out, therefore, deliberately to solve the whole question of
airplane stability. There was the fore and aft or horizontal stability,
for which Lillienthal had swung his legs forward and backward; there
was in addition the sidewise or lateral stability for which Lillienthal
had swung his legs to left and right. The fundamental requirements
to be met were that during flight the glider should be kept in its
proper attitude without diving or rearing up, and without rolling into
an attitude where one wing tip was higher than the other, i.e., the
machine was to be kept level in both directions.
[Illustration: First Wright glider.
With front elevator, shown flying empty as a kite.
Final Wright glider.
With rudder and elevator. Note right wing warped downward to raise
right wing tip.
A successful downhill glide. Pilot lies prone on bottom wing.
FIG. 4.]
=Fore and Aft Control.=—After some preliminary trials the Wrights
found that the fore and aft balance could be controlled by an elevator
or horizontal rudder, supported on outriggers on the front of the
airplane, and operated by a lever. If the pilot found the glider
pitching too much downward, and tending toward a dive, he would tilt
the elevator upward by moving the lever, thus turning the glider back
into its proper attitude. This elevator in modern machines is back of
the airplane, a better place for it than was chosen by the Wrights.
It may be said that their chief reason for first putting it in front
was that they could see it there and observe its effect. They soon
realized that the rear location gave easier control, and they acted
accordingly.
=Lateral Control.=—After satisfying themselves regarding fore and aft
control, the Wrights took up lateral control. Their problem was to
devise a means for keeping the span of the wings level so that when for
any reason one wing tip should sink lower than the other, it could be
at once raised back to its proper position. Lillienthal had tried to
do this by swinging his legs toward the high side; the shifted weight
restoring the position. The Wrights, to obviate this inadequate method,
bethought themselves to restore equilibrium by means of the wind itself
rather than by gravity. They observed an interesting maneuver employed
by a pigeon which seemed to secure its lateral balance in exactly
the way they wanted; this bird was seen to give its two wings each a
different angle of attack, whereat one wing would lift more forcibly
than the other, thereby rotating the bird bodily in any desired amount
or direction about the line of flight as an axis. To copy this bird
apparatus in a Wright glider, it was found sufficient to alter the
angle of the wing tips only, leaving the chief part of the supporting
surface in its original rigid position. In other words, the wing tips
were to be warped; the one to present greater angle of attack, the
other less angle, exactly as in the case of the pigeon. Suppose the
airplane to develop a list to the left, the wing on that side sinking,
the pilot was to increase the angle at the tip of this left-hand wing
by moving the warping lever, and at the same time decrease the angle
of the right-hand wing by the same lever. He was to hold this position
until the airplane was righted and brought back to level position.
This arrangement proved to have the effect anticipated and maintained
stability easily on a glider much larger than Lillienthal ever managed
with his leg-swinging method.
=Directional Control.=—We have now followed the development by the
Wrights of airplane control as regards:
1. Fore and aft or “pitching” motion, accomplished by an elevator
operated by lever.
2. Lateral or “rolling” motion accomplished by wing warping operated by
a second lever.
These were the only controls used in the earliest gliders. It remains
to consider the third element of control, viz:
3. The directional or “yawing” control, which is accomplished by an
ordinary vertical rudder operated by a third lever.
The Wrights found the warping had all the effect anticipated but had
also certain secondary and undesirable effects. Whenever they applied
the warping lever to correct the rolling motion, the glider responded
as far as rolling control was concerned, but at the same time would
“yaw” or swerve out of its course to right or left. This was a serious
complication. For, in the moment of swerving, the high wing which they
desired to depress would advance faster than the low wing, and solely
by its higher velocity tended to develop a greater lift and thereby
neutralize the beneficial effect of the warp. In many of their early
glides, because of pronounced swerving, the warp effect was entirely
counteracted and failed to bring the glider back to level; with the
result that one wing tip would sink, at the same time swinging backward
until the machine was brought to the ground. No amount of controlling
could prevent this.
After much bewilderment on this point, the Wrights observed that
whenever a wing tip was warped to a large angle its resistance became
relatively greater and it slowed up while the opposite side went ahead.
They at once hit upon the idea of a rudder, previously considered
unnecessary, which they believed could be turned in each case of
yawing just enough to create a new and apposing yawing force of equal
magnitude.
They therefore attached a rudder at the rear, connecting its tiller
ropes to lever No. 2, and giving this lever a compound motion so that
one hand could operate either warp or rudder control independently (or
simultaneously in proper proportion to eliminate the yawing tendency
above mentioned). This combination is the basis of the Wright patents
and is essential in airplanes of today.
Great success now ensued in their gliding experiments; the machine was
always in perfect control; could be manipulated in any desired manner;
turned to right or left, or brought down to earth with safety.
Thus were the three elements of control applied by the Wrights to their
glider and the problem apparent in Lillienthal’s death was solved.
The next step was to install a power plant able to maintain forward
speed without resorting to coasting downhill by gravity; and therefore
capable of producing a horizontal flight.
In developing a power flyer aside from the question of control the
proper design was arrived at as follows:
=Efficiency of Wings.=—The Wrights knew from Langley and Chanute that
flat wings were inefficient and useless, and curved wings essential;
they did not know whether the amount of curvature mattered much. To
find this out by trials in gliding would be slow and expensive. They
adopted a better way—the wind-tunnel method, wherein small-scale models
were tested and compared for efficiency in a blast of air. They made
their wind tunnel 16 in. in diameter and created a powerful air blast
through it by means of an engine-driven fan. Small models of wings
were placed in the center of this confined air blast, mounted on a
balance arm which projected into the tunnel from the outside. The
air forces and efficiency of the models were thus measured. A large
variety of shapes were tested and one was selected as best of all from
the standpoint of curvature and rounded wing tips. This shape was
adopted in their flyer, and though on a much larger scale fulfilled
the predictions made for its efficiency in the indoor wind-tunnel
experiments.
The Wright glider was, of course, a biplane model. They tested a small
6-in. model biplane and found that the two wings together were less
efficient than either wing by itself. However, other considerations,
such as rigidity of trussing, decided them to adopt the biplane rather
than a monoplane arrangement.
=Low Resistance to Forward Motion.=—The Wrights used their wind tunnel
also in choosing for the struts of their airplane a shape which would
present least head resistance to forward motion. They found that a
square strut had a resistance which could be decreased by changing
the shape to resemble a fish. The resistance of the pilot himself was
decreased by making him lie prone, face downward on the bottom wing.
=Propeller Efficiency.=—Although little data on the subject of
propeller efficiency was available to the Wrights, they were able to
arrive at a very creditable design wherein two propellers were used,
driven from a single motor, and rotating one each side of the pilot.
The mechanical difficulties which have since embarrassed the use of two
propellers were less with the Wrights because they were dealing with
smaller horsepowers than are in use today; they therefore were able to
realize a very high propeller efficiency.
=Motor.=—When the Wrights were ready to apply a motor to their glider,
they found it impossible to secure one light enough, and had to set
about building one themselves. They adopted a four-cylinder type,
water-cooled, and their aim was to save weight and complication
wherever possible. Their first motor gave about 12 hp., which was
raised to a higher and higher figure by subsequent improvements until
it reached 20 hp. In its earliest stages it was able to give sufficient
power for short horizontal flights.
=Means of Starting and Landing.=—One reason the Wrights could use such
low horsepower was that they employed auxiliary starting apparatus to
get up original speed. They knew that less horsepower was necessary to
fly an airplane after it was once in the air than was necessary to get
it into the air at the start, and they therefore rigged up a catapult
which projected their airplane forward on a rolling carriage with great
force at the start, so that all the motor had to do was to maintain
the flight in air. The Wright airplane had at first no landing wheels,
and was provided only with light skids on which it could make a decent
landing. Present-day airplanes, of course, have wheels on which to roll
both at starting and at landing and their motors are powerful enough to
eliminate the necessity for a starting catapult.
[Illustration: (_Courtesy American Technical Society and Scientific American
Supplement._)
FIG. 5.—Details of Bleriot XI monoplane.]
=Bleriot’s Contribution to Aviation.=—Bleriot experimented a great
many years before he attained success and did so years after the
Wrights had successfully flown. But when he did obtain success, his
great ingenuity produced features of design which were a decided step
forward. He added a body to the airplane and produced a machine which
instead of being a pair of wings with various appendages, was a body
to which wings were attached, giving a more shipshape and convenient
arrangement. The motor, instead of being located beside the pilot as
in the Wright machine, was put in the very front of the body ahead of
the pilot where it was not likely to fall on him in case of a smash.
This location of the motor entailed the use of a single propeller at
the front, a “tractor” screw as it was called, less efficient than the
double propeller of the Wrights, but better from the standpoint of
mechanical convenience. The body of a Bleriot, which was quite similar
to the body of any bird in its general arrangement, projected to the
rear in a tapering form and carried at the rear a rudder and elevator.
The motor, pilot and tanks were thus enclosed within the body and away
from the wind. Bleriot’s contributions were then, better location of
the motor, adaptation of the body or “fuselage,” elimination of the
front elevator and substitution of the rear elevator.
=Nieuport and Fokker’s Contribution to Aviation.=—A further advance
on Bleriot’s design was made by Nieuport and later by Fokker. The
former utilized the fuselage principle of Bleriot and enclosed the
whole framework, front and back, to give a stream-line form, and even
went so far as to make wind-tunnel experiments from which he was able
to choose a very efficient fuselage shape as well as wing and strut
efficiency.
[Illustration:
(_From Hayward’s “Practical Aeronautics.”_)
FIG. 6.—Nieuport monoplane.
Representing an advance in speed, due to covered stream-line body.]