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.
Fig. 42.—Diagram of Curtiss Hydro-aëroplane. (Scientific American.)
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.
Fig. 43.—The Etrich Monoplane of 1910.