As shown in Plate XXXI, Fabre’s hydro-aëroplane was substantially a monoplane mounted on three richochet floats. It was propelled by a screw at the rear, and controlled in flight by the usual three-torque system, in this case consisting of horizontal rudders in front, vertical rudders front and rear, and suitable mechanism for twisting the wings. The floats were hollow to give them static buoyancy; they were curved fore and aft like wings, to give them dynamic lift, both in water and in air; they were elastically constructed with thin veneer bottoms and flexibly attached to the framing, so as to endure the severe buffeting, at high speeds, against the uneven water surface; they were capable of landing the machine safely on a sandy beach or meadow, as well as on the water. Indeed, a plan was conceived for rising and alighting on land and water indifferently.
The first machine weighed in flight 950 pounds and spread 280 square feet of surface, giving a loading of 3.4 pounds per square foot. It was driven by a 50-horse Gnome engine actuating a Chauvière propeller 7.5 feet in diameter. In the trials of March 28th, the machine cleared the water at a speed of 34 miles per hour, and flew about one-third of a mile, at an elevation of two to three yards; then at the will of the operator it alighted softly on the water.
The structural design of the Fabre monoplane was novel and unique, not to say radical. The wing framing consisted of a single Fabre trussed beam with ribs attached like the quills of a bird, over which was stretched the light sailcloth cover, then laced to the beam. The girder itself was formed of two ash planks eight inches wide by one-fourth inch thick trussed together by flat steel plates zigzagging trelliswise between them. As all parts of the beam cut the air edgewise it offered very little resistance, while at the same time being very strong. The ribs being attached only at one end allowed the sailcloth to be quickly slipped on and off for washing and proper care.
The characteristic features of Fabre’s wing construction were adopted by Paulhan in his novel and picturesque biplane shown in Plate XXXI. Trussed beams were used for all parts requiring considerable stiffness, the longitudinal ones being covered with fabric to reduce the resistance. The wings whose solid ribs were fastened only at their front ends were quite elastic, a quality conducive to stability, as long taught by writers[55] on aviation. In addition to the front rudder, there was at the rear a horizontal rudder with a vertical one just before it. To reduce the air resistance further the pilot and passenger were to sit tandem in a torpedo-shaped car with the 50-horse Gnome engine and fuel tank back of them. Beneath the longitudinal girders were two Farman skids flanked with the usual wheels, elastically connected. The machine, besides flying well, was readily demountable. The wings could be quickly removed, thus allowing the biplane to enter a door fifteen feet wide. The entire machine could be packed in a case 15½ feet long by 3¼ feet square, the whole case cubing less than six solid yards. Hundreds of them, therefore, could be stowed away in an ocean cruiser.
The flying quality of adequately designed flexible aëroplanes is well illustrated by the swallowlike monoplane shown in Fig. 43. This airy creation of the distinguished Austrian engineer, Igo Etrich, came into public prominence in the spring of 1910, though it had been developing privately for half a decade or more. On May 14th, near Vienna, it carried pilot Illner 84 kilometers in 80 minutes, at an elevation of 300 meters, thus surpassing all previous Austrian records for distance, duration and altitude. Its successor, Etrich IV, had wing tips still more turned up, and possessed such stability that during the meet at Johannisthal in October, Illner circled the pylons with his hands off the warping levers. At times he wheeled round curves of only ten meters radius, the whole machine tilted at an alarming angle, yet maintaining its poise with the natural ease and grace of a soaring albatross.
The prominent feature of Etrich’s monoplane was the elastic construction of its wings and tail. Across the rigid main bars of each wing were fastened numerous ribs with bamboo terminals, thus making the rear margin and tip of the wing flexible. Similarly the tail, or horizontal rudder, was framed of bamboo. Hence the pilot, by use of control wires, could flex both the wing margins and the tail up and down at will, to steer the machine, or he could let go the controls and allow the distorted surfaces to spring into their normal positions, and the machine to pursue the even tenor of its way. Moreover, the gusts and whirls in the air, on striking the elastic rear margins of the tail and wings, exert a propulsive effort. Thus could be utilized the wind’s energy of turbulence, as indicated by the present writer in 1893, in a paper on “Windgusts and Their Relation to Flight,” published in the Proceedings of the International Conference on Aërial Navigation of that year. In passing it may be remarked that many other aëroplane designers, notably Bréguet, have emulated Mr. Etrich, though unconsciously perhaps, in providing elastic ribs, hinges or pivots to permit the rear parts of the wings and tails of their machines to yield freely to intentional or unusual impulses, and then spring back to their normal positions.
The carefully elaborated monoplane of Robert Esnault-Pélterie, which had been steadily improving for eight years, had now attained great perfection of finish, and merited prominence in actual flight. As shown in Plate XXIX, it had a general resemblance to the Antoinette, though differing throughout in its manifold details. The stream-line body was of steel tubing, braced with wire, and tightly covered with smooth fabric to reduce resistance. A five-cylinder R. E. P. motor in front connected directly with the two-blade propeller. The pilot sat between the wings with the passenger before him at the center of gravity, both having control levers when desired for instruction. The wings could be warped and the rudders, at the end of ample empennage planes, occupied the extreme rear as shown. An elastically cushioned skid between the two freely turning wheels served to absorb the shock of hard landing, though usually not touching the ground. The R. E. P. monoplane of 1910 was a very graceful, swift and strong machine, of marked efficiency.
As always happens in the many-minded development of a complex invention, the general exhibition and use of the aëroplane led toward uniformity of design. This became particularly noticeable during the world-wide demonstrations of 1909 and 1910. Whatever predilection the inventor might have for his own devices, he would rather cast them aside than lose at the tournament and in the market. Without a monopoly of the flying art, he could ill afford to retain too affectionately his own second-rate device in competition with a rival having a more effective one. Accordingly there was a judicious and general adoption of those devices which had proved best in practice, from whatever lowly intellect they had emanated. Thus there was a marked tendency to the general use of starting wheels, landing skids, large warping surfaces, and, in racing machines, to the stream line concentration of the load, and the severe elimination of resistance.
A few examples will illustrate this tendency to choose the most practical devices from the world’s general stock. The Wright brothers, who, following Maxim, had been ardent votaries of the forward horizontal rudder, discarded this in 1910 for the elastic rear horizontal rudder introduced by Etrich. At the same time they abandoned the antiquated catapult introduced by Langley, and adopted the combination of wheels and skids introduced by Farman. In their racing machine they no longer placed the aviator beside his engine, presenting a broad front to the wind, but, like Curtiss and foreign designers, they placed the driver and power plant in line, to diminish the atmospheric resistance. These manifold and timely improvements indicate clearly the advantages to mankind of an “open door” in a crescent art.
But if the Wrights adopted the most successful devices of their neighbors, these in turn were not slow to reciprocate that policy. There was ample recognition of the merit of the combination of warping sustainers and double rudder proposed by scientific men before the advent of power aëroplanes, and so admirably employed by the Wrights and Prof. Montgomery in their early coasting flights. The warping wing was quite generally used on monoplanes in 1910; not to mention the ailerons, which frequently were an adaptation of the same principle.
As further illustrations, it may be noted that Voisin brothers adopted the Farman ailerons and abandoned the cellular type of sustaining surface introduced by Hargrave, finding the vertical surfaces strongly frictional and unnecessary for lateral equilibrium, in presence of the ailerons. They also abandoned the forward horizontal rudder, seeing that it could very well be omitted. On the other hand, it must be observed that the Farmans, Sommer and Curtiss still retained the combined fore and aft rudder. Curtiss and Farman also tried their hands at monoplane construction, though without abandoning the biplane. The most famous monoplanists, however, held firmly to their first love. In this they were emulated by many new designers, Nieuport, Hanriot, Déperdussin, etc. These show a marked tendency to employ smoothly covered hulls shaped after the fish or torpedo.
To drive the little aëroplanes so far developed, especially the racers, there was a general preference for a single-screw propeller mounted directly on the engine shaft, though doubtless for machines weighing many tons a multiplicity of such propellers would be used. Theoretically the advantage of twin screws was conceded, but in practice they were employed by very few constructors. The Chauvière wooden propeller was the favorite in France, and was approved by the constructors of propellers elsewhere, at least in its general features. The Voisin firm, indeed, still adhered to the metal propeller, and occasionally some experimentalist employed the more venerable French screw consisting of radial sticks covered with fabric. But the great records in the sporting world were achieved with solid wooden propellers.
A special chapter would be required to describe the various motors, even cursorily. Their relative values, however, may be summarized in the following brief words by Réné Gasnier, in the Aërophile for November, 1910:
“Last year we had but few light types; this year there is no dearth of them, and at their head stands that admirable motor Gnome, which has enabled aviators to accomplish all their fine performances. At first many persons had no confidence in the future of the rotatory motor. One must bow to the facts; on considering the nature of this motor it is seen to be of an admirable simplicity. It is evidently the typical aviation motor, and an approach toward the veritable rotatory motor which later will be the turbine. Numerous motors of four to eight cylinders are very well spoken of, but none attain the lightness of the Gnome. Among the air-cooled motors the Esnault-Pélterie is remarkable for the series of trials it has endured, and among water-cooled motors we may cite the splendid performance of the Antoinette—2,100 kilometers in one week at the Bordeaux meeting. This would be quite a good run even in an automobile. It is noticeable that the aëroplane motor tends distinctly to differentiate itself from its senior, the automobile motor, and assume a type absolutely adapted to its special work. In addition to the greatest possible lightness, a demand now arises for a slight consumption of fuel, and a range of speed which is indispensable for landing. It is dangerous to descend rapidly with the motor at full speed; on the other hand, in cutting off the ignition to glide down, one risks not being able to restart the motor, if need be, while if the motor relax sufficiently the descent takes place in perfect security. It suffices to speed up at the right moment.”
The practical utility of aviation began now to be questioned. The aëroplane had passed the primary epoch of experimental development and was becoming a standard article of manufacture representing a considerable industry. But what was it all worth? Aviators had flown faster than the eagle, higher than the clouds, farther than the common distance from metropolis to metropolis. Schools were licensing new pilots from day to day. But what career had these before them, and what essential function in the affairs of humanity could they perform? Some, indeed, might fit themselves for aërial service in warfare, some for the pleasant profession of amusing and entertaining mankind; but in the serious business of life, what important rôle could the air men hope to play? This was the pertinent inquiry, and it was largely a question of the reliability and economy of the aëroplane. Improvement in these two elements might therefore receive attentive consideration in the immediate future.
The reliability of the aëroplane depends partly on its environment, partly on its plan and structure, partly on the skill of its pilot. The pilot’s skill had been admirably developed in the tournaments and public exhibitions. The aërodynamic design conducive to stability and steadiness, the structural design conducive to maximum strength and resiliency, uniformly proportioned to the stress and work of each part of the complex machine; and above all the design of the motor, to ensure it against a thousand foibles—all these could be improved by the patient methods of theoretical and experimental science. The environment could, of course, be chosen. At first only the most favorable regions need be attempted for regular transportation, regions of level plain and farm land, or of lake and river surrounded by country not too rough and precipitous.
The general cost of the aëroplane to mankind depends on its plan and structure, on the methods of manufacture, on the material running expense; but its particular cost to the passenger is determined largely by the cupidity or business acumen of those who furnish the machine and those who operate it. Naturally when the world first awoke in the morning of practical sporting aviation, with a sudden and strong relish for flying, the prices would be fabulous, not to say ridiculous. During that hour no commercial transportation could be contemplated. But without monopoly the prices must quickly abate; for neither the manufacture nor manipulation of the aëroplane demand rare ability or training. The cost of manufacture would promptly be diminished by means of specialized tools and operatives, immediately upon the assurance of large and continuous orders. The cost of pilotage would become insignificant when a single chauffeur could take a dozen passengers on one aëroplane.
So much for the human and external elements in the cost of aviation. The inherent and material cost of the aëroplane could also be reduced, though perhaps less readily. It was unlikely that the machine would be built of much cheaper materials, or made much lighter per pound of cargo. Nor were such improvements of so much importance since they would affect only the first cost of the flyer. But an increase of aërodynamic efficiency in the propeller and aëroplane proper, together with increased thermodynamic efficiency in the motor, would materially lower the current cost of transportation at any given speed. These improvements would require careful research in the laboratory and patient trial in the workshop and field. The refinement and perfection of the aëroplane might therefore be looked for in those communities where men have sufficient foresight, enterprise and liberality to endow research, and to encourage the science and the art of aviation to supplement each other.