History of Aviation - Chapter 1
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 manfiight 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 remodeled 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.
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.
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; ~at 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 far some distance without striking The ground and 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 LillienthaI'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 differen1 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 so thing worth while in the way of artificial flit 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 sideo _ 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 level2 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, accom plished 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 slowly 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 ai
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 e cy in the indoor wind-tunnel experiments.
right glider was, of course, a biplane model. y tested a small 6-in, model biplane and found 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 horsepower's 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 bad 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 lip., which was raised to a higher and higher figure by subsequent improvements until it reached 20 lip. 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.
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 ai4 to choose a very efficient fuselage shape as well and strut efficiency.