Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/333

F LIGHT 321 screw (a a), the india-rubber in a state of torsion (/) extends. l]y fixiw the lower screw and turning the upper one a sufficient number of times the requisite degree of torsion io. 33. Helicoptcre or Screw-Model, by M. Penand. (1872.) and power are obtained. The apparatus when liberated flies into the air sometimes to a height of 50 feet, and gyrates in beautiful large circles for a period varying from 15 to 30 seconds. M. Penaud next directed his attention to the construction of a model, to be propelled by a screw and sustained by an elastic aero-plane extending horizontally. Sir George Cayley, it should be stated, proposed such a machine in 1810, and Mr Henson (as will be shown subsequently) constructed and patented a similar machine in 1842. Several other inventors succeeded in making models fly by the aid of aero-planes and screws, as, e.g., Mr Stringfellow in 18 17, 1 M. du Temple in 1857, and M. Jullien in 1858. As rigid aero-planes and screws were employed in the construction of these models they flew in a hap-hazard sort of a way, it being found exceedingly difficult to confer on them the necessary degree of stability fore and aft and literally. M. Pe naud succeeded in overcoming the diffi culty in question by the invention of what he designates his automatic rudder. This consists of a small elastic aero-plane placed aft or behind the principal aero-plane which is also elastic. The two elastic aero-planes extend horizontally and make a slight upward angle with the horizon, the angle made by the smaller aero-plane (the rudder) being slightly in excess of that made by the larger. The motive power is india-rubber in the condition of torsion ; the propeller, a screw. The reader will under stand the arrangement by a reference to the accompanying drawing (fig. 3! ). _ Fro. 39. Aero-plane model with automatic rudder, a a, clastic aero-plane; (> b, automatic rudder; c e, aerial screw centred at /; J, frame supporting acro-planc, rudder, and screw; e, india-rubber, in n state of torsion, attached to hook or crank at/. By holding the aero-plane (a a) and turning the screw (c r) the necessary power is obtained by torsion. (M. lY naud, 1872.) Models on the aero-plane screw type may be propelled by two screws, one fore and one aft, rotating in opposite 1 Mr Stringfellow constructed a second model, which was exhibited r.t the exhibition of the Aeronautical Society (Crystal Palace), in 1868. It is described and figured further on. directions ; and in the event of only one screw being employed it may be placed in front of or behind the aero plane. When the model is wound up and let go it descends about two feet, after which, having acquired initial velocity, it rises and flies in a forward direction at a height of from 8 to 10 feet from the ground for a distance of from 120 to 130 feet. It flies this distance in from 10 to 11 seconds, its mean speed being something like 12 feet per second. From experiments made with this model, M. Pe naud calcu lates that one horse power would elevate and support 85 Ib. Mr Brown has also written (1874) in support of elastic aero-bi-planes. His experiments prove that two elastic aero planes united by a central shaft or shafts, and separated by a wide interval, always produce increased stability. Tho production of flight by the vertical flapping of wings is in some respects the most difficult, but this also has been attempted and achieved. M. Pe naud and M. de Villeneuve have each constructed winged models. Professor Marey was not so fortunate. He endeavoured to construct an artificial insect on the plan advocated by Borelli, Straus-Durckheim, and Chabrier, but signally failed, his insect never having been able to lift more than a third of its own weight. MM. de Villeneuve and Pe naud constructed their winged models on different types, the former selecting the bat, tho latter the bird. M. Villeneuve made the wings of his arti ficial bat conical in shape and comparatively rigid. Ho FIG. 40. Artificial flyinp bird, rt ?> t d, a I c d , elastic wings, which twi.^t and untwist when made to vibrate; a b, a b , anterior margins of wings; c d, c il , posterior margins of wings; c, c , inner portions of wings attached to central shaft of model by clastic bands at c; /, india-rubber in a state of torsion, which provides motive power, by causing the crank situated between the vertical wing supports (;/) to rotate: as the crank revolves the wings are made to vibrate by means of two rods which extend between the crank and the roots of the wings; /(, tail of artificial bird. (M. l enaud, 1872.) controlled the movements of the wings, and made them strike downwards and forwards in imitation of natural wings, as described by Professor Pettigrew. His model possessed great power of rising. It elevated itself from the ground with ease, and flew in a horizontal direction for a distance of 24 feet, and at a velocity of 20 miles an hour. M. Pe naud s model differed from M. de Villeneuve s in being provided with elastic wings, the posterior margins of which in addition to being elastic were free to move round the. anterior margins as round axes (see p. 313, fig. 24). India-rubber springs were made to extend between the inner posterior parts of the wings and the frame, corresponding to the backbone of the bird. A vertical movement having been communicated by means of india-rubber in a state of torsion to the roots of the wings, the wings themselves, in virtue of their elasticity, and because of the resistance experienced from the air, twisted and untwisted and formed reciprocating screws, precisely analogous to those originally described and figured by Professor Pettigrew in 1867. M. Pe naud s arrangement is shown in fig. 40. If the left wing of M. Pe naud s model (a l>, c d of fig. 40) be compared with the wing of the bat as drawn by IX. 41