168 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. Li 



transverse frame are joined together by the " bed plates " L, which are of I- 

 beam section, and have mounted on their outer faces the bearings which sup- 

 port the propeller shafts. At V are bevel gears mounted on the propeller shafts, 

 which are driven by co-acting bevel gears, .1/, moulded on the outer ends of the 

 transmission shafts, 0, the latter being at this point firmly supported in bear- 

 ings mounted on the inner faces of the bed plates and steadied by the intermedi- 

 ate bearings, N. The two transmission shafts are seen to be not in line, the ro- 

 tary cylinder engine that was then under construction requiring this arrange- 

 ment. The bed plates, L, are further stiffened by the brace tubes, K, and the 

 transverse frame is braced against the thrust of the propellers by the tubes J. 

 The four tubes, P, unite at their upper ends to form what was designated as 

 the upper " pyramid," and the wires, 8 and T, radiate from its apex to the 

 rear and front, respectively, of the main frame. The lower " pyramid," on the 

 under side of the frame, also has similar wires running fore and aft. The 

 main portions of both frames are further strengthened by their sub-frames, 

 which merge together, and the main tubes of the main frame are individually 

 stiffened in the vertical piano by a minor system of guying. The scales shown 

 in the photographs are calibrated in metres. 



It is to be particularly noted that the midrod, which bad heretofore formed 

 the backbone of the main frame, was now made to act merely as a means of at- 

 taching the wings to the frame, the main strength of the frame being furnished 

 by the two parallel fifty millimetre tubes which extended the entire length of 

 the frame and which, reinforced by the guy-wires, formed a truss not only more 

 rigid transversely, but also many times stronger in its ability to resist torsional 

 strains than could be secured by a single tube of equal weight. In this plan of 

 constructing the main frame, the pyramids constituted a very important ele- 

 ment, for with the guy-wires arranged as they were it was impossible for any 

 portion of the frame to experience a stress which was not transmitted in some 

 way to the pyramids, in the frame, as here shown, these pyramids were 

 formed of tubes 15mm. in diameter, 0.5mm. thick, stiffened against budding 

 under the end pressure by means of the cross-braces, which united them near 

 their midpoints. 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, Imt also provided a means for holding the aerodrome to the launch- 

 in-- 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 " bear- 

 ing points " of the machine firmly against the uprights on the car. In fact, the 

 particular arrangement of these pyramids was largely determined by this neces- 

 sity for providing means for holding the aerodrome to the launching car, and 

 the form which seemed host suited to the purpose was duplicated on the up- 

 per side of the frame. 



