S. P. Langley

“ If we suppose it to realize 2 per cent of the theoretical energy contained in the fuel, we shall be assuming more than was actually obtained. The energy of the fuel cannot be obtained at all, of course, without boiler and engine, whose weight, for the purpose of the following calculation, must be added to that of the fuel; and if we suppose the weight of the boilers, engines and water, for a single minute’s flight, to be collectively ten pounds, we shall take an optimistic view of what may be expected under ordinary conditions. ”

“ To secure this balance, or equilibrium, we know in theory, that the center of gravity must be brought nearly under the center of pressure, by which latter expression we mean the resultant of all the forces which tend to sustain the aerodrome; but this center of pressure, as may in fact be inferred from “Aerodynamics,”10 varies with the inclination of the surface. It varies also with the nature of the surface itself, and for one and the same surface is constantly shifted unless the whole be rigidly held, as it is on the whirling-table, and as it cannot be in free flight. ”

“ To such men as Mr. Langley an unsuccessful experiment is not a failure but a means of instruction, a necessary and often an invaluable stepping-stone to the desired end. The trials of the large aerodrome in the autumn of 1903, to which the curiosity of the public and the sensationalism of the newspapers gave a character of finality never desired by Mr. Langley, were to him merely members of a long series of experiments, as much so as any trial of one of the small aerodromes or even of one of the earliest rubber-driven models. ”

“ He began his investigations at a time when not only the general public but even the most progressive men of science thought of mechanical flight only as a subject for ridicule, and both by his epoch-making investigations in aerodynamics and by his own devotion to the subject of flight itself he helped to transform into a field of scientific inquiry what had before been almost entirely in the possession of visionaries. ”

“ If the aerodrome is of sufficient size and power to carry a human being it is, of course, possible merely to supply an efficient means of controlling the lateral and horizontal equilibrium of the machine and depend upon the intelligence and skill of the operator, as developed by practice and experience, to maintain the proper equilibrium of the machine while in the air. ”

“ No one is unaware that many experimenters have been engaged in trying to execute free mechanical flight, and although the demonstration which I furnished in 1891 [“Experiments in Aerodynamics,” 1891] of its theoretical possibility with means then at our disposition, seemed conclusive, so long a time has elapsed without practical results, that it might be doubted whether these theoretical conditions are to be realized. I have thought it well, then, to occupy myself with the construction of an aerodrome with which I might put my previous conclusions to the test of experiment. ”

“ Langley had made the firm resolution not to undertake the construction of a large man-carrying machine, as he realized that his multitudinous administrative duties left him practically no time available for original research, yet the longing to take the final great step of actually transporting a human being through the air, which the successful flights of the models had now for the first time in the history of the world actually proved to be possible, soon became irresistible. ”

“ My most primitive observation with small gliding models was of the fact that greater stability was obtained with two pairs of wings, one behind the other, than with one pair (greater, that is, in the absence of any instinctive power of adjustment) .
This is connected with the fact that the upward pressure of the air upon both pairs may be resolved into a single point which I will call the “center of pressure,” and which, in stable flight, should (apart from the disturbance by the propeller thrust) be over the center of gravity. ”

“ CONSTRUCTION AND TESTS OF THE LARGE ENGINE
The main requirement in an engine for an aerodrome—aside from reliability and smoothness of operation, which are necessary in an engine for any kind of locomotion—is that it shall develop the greatest amount of power for the least weight. It is, therefore, desirable to reduce the weight and number of parts of the engine to the very minimum, so far as this can be done without sacrificing reliability and smoothness of running. ”

“ The weight of the aviator, it is true, constituted an appreciable part of the flying weight of the large machine, and it at first seemed possible to lower the center of gravity by placing him at a considerable distance below the line of thrust. But it was recognized from the beginning that the aviator would probably have to give a great deal of attention to any form of engine in order to insure its working properly, and his position must, therefore, be selected with a view to the proper supervision of the engine and without regard to its effect on the center of gravity. ”

“ It was, however, by no means possible to build the large aerodrome within the permissible limits of weight by simply increasing the various parts of the models according to some predetermined function of the size of the whole.
The fundamental difficulty is that inevitably, by the laws of geometry, which are mere expressions of the properties of space, if a solid of any form is magnified, the weight increases as the cube, while the surface increases only as the square, of the linear dimensions. ”

“ The writer is firmly convinced that the aerodrome is not only correct in principle but that it possesses no inherent faults or weaknesses, and that the success which the work deserves has been frustrated by two most unfortunate accidents in the launching of the machine. Other plans of launching, several of which were studied out during the early stages of the work on the large machine, would have avoided the accident which did occur, but, of course, might have produced others possibly even more disastrous, but which could be determined only by actual trial. ”

“ Where an engine has a large and heavy fly-wheel running at a high rate of speed, the nicety of adjustment of the sparking arrangement is not so essential, for the fly-wheel acts as a reservoir of energy and tends to smooth out the rough and jerky impulses which would be otherwise introduced by slight variations in the force of the explosions in the cylinders. In constructing an engine for an aerodrome, however, the permissible weight of the engine is so very small that the use of a fly-wheel having sufficient weight to act as an energy reservoir is practically prohibited. ”

“ This experience with propellers very strongly emphasizes the fact that on any flying machine the strains which are apt to be met with in the open air must be allowed for in the proportioning of the parts of the machine. But since an indiscriminate increase of strength in all the various parts of the machine would entail a prohibitory weight, very careful judgment, based on experience, will have to be exercised in deciding just where added strength must be employed, and also where the “live strains” are not apt to exceed very appreciably the calculation for statical conditions. ”

“ It was, however, very evident that, although the correct balancing which would insure equilibrium for a few minutes might soon be attained, the machine, lacking a human intelligence to control it, must be provided with some mechanism which would tend to restore the equilibrium, the conditions of which must necessarily change in a machine depending on the air for its support. ”

“ It is sufficient to call attention to the fact that in an engine having five cylinders arranged radially, all of the reciprocating parts are balanced for all forces of the first, second and third orders. As it is only the reciprocating parts which give any trouble in balancing any engine, the unbalanced rotating parts being readily balanced by placing an equal weight at an equal distance from the center of rotation, and on the opposite side thereof, it is readily seen that the properties of balancing which are inherent in this type of engine are unusual. ”

“ The radial arrangement of the cylinders is thus seen to give not only an engine with the smallest number of parts, each of which is as far as possible worked to a uniform amount during each complete revolution of the crank shaft, but it also gives a very compact and readily accessible mechanism with its center of gravity coincident with its center of figure, and with the liability of damage to it, in case of a smash of the vehicle on which it is used, reduced to the minimum from the fact that the greatest weight is located at the strongest part. ”

“ If one is building bridges, houses, and similar structures, where weight is not a prime consideration, it would be criminal negligence to fail to provide a sufficient “factor of safety,” or what in many instances may be more properly termed a “factor of ignorance,” while at the present time the insistence on large factors of safety in machines intended to fly would so enormously increase the weight that, before one-half the necessary parts were provided, the weight would be many times what could possibly be supported in the air. ”

“ EXPERIMENTS IN THE OPEN WIND
I have pointed out21 that an indefinite source of power for the maintenance of mechanical flight, lies in what I have called the “internal work” of the wind. It is easy to see that the actual effect of the free wind, which is filled with almost infinitely numerous and incessant changes of velocity and direction, must differ widely from that of a uniform wind such as mathematicians and physicists have almost invariably contemplated in their discussions. ”

“ The scale of the actual construction was adopted under the belief that it must be large enough to carry certain automatic steering apparatus which I had designed, and which possessed considerable weight. I decided that a flying machine if not large enough to carry a manager, should in the absence of a human directing intelligence, have some sort of automatic substitute for it, and be large enough to have the means of maintaining a long and steady flight, during which the problems (which the rubber-driven models so imperfectly answered) could be effectually solved. ”

“ I beg the reader, therefore, to recall as he reads, that everything here has been done with a view to putting a trial aerodrome successfully in flight within a few years, and thus giving an early demonstration of the only kind which is conclusive in the eyes of the scientific man, as well as of the general public—a demonstration that mechanical flight is possible-—by actually flying. ”

“ At this time (1898) the automobile industry, through which has come the development of the gasoline engine, was in its infancy, and there were few builders either in the United States or Europe who were attempting anything but rough and heavy construction. Many of them were enthusiastic over the possibilities of the internal combustion engine, and were ready to talk of devising such an engine as the aerodrome would require, but few were willing to guarantee any such definite results as were demanded. ”

“ While the sole function of the upper pyramid was to serve in the system of guying the frame, the lower pyramid not only served a similar purpose, but also provided a means for holding the aerodrome to the launching car in the process of launching it, the clutch-hooks gripping around the short horizontal tube at the apex of the pyramid and thus drawing the “bearing points” of the machine firmly against the uprights on the car. ”

“ Since the power required to rotate the rotor plates, with a uniform amount of water in the drums, varies as the cube of the speed, it is readily seen that it is impossible for the engine to race or injure itself by running away, as frequently happens where there is no engine governor and Prony brakes are used to measure the power.
In the early tests the engine was never allowed to develop more than 40 horse-power, as it was feared that by letting it develop more, which it was clearly seen to be capable of, it might be injured and cause a delay in the tests of the aerodrome. ”