FIFTY YEARS OF FLYING PROGRESS — LOENING 209 



twin-engine configuration. Before the arrival at this final type we also 

 went through a trimotor period, notably the ubiquitous Ford trimotor 

 and the Fokker. But this type did not last except for the Ford, which 

 was more widely used and was probably one of the most successful 

 airplanes in history. 



STABILITY AND CONTROLS 



Fifty years have done much to the airplane's control surface, 

 stability, and tail configuration. Reexamining the early Wright plane 

 from the standpoint of our present-day knowledge, we must first pay 

 tribute to the acrobatic balancing skill necessary in order to keep the 

 airplane flying straight. The "Kitty Hawk" was controllable but 

 completely devoid of any natural stability. This applied also to the 

 early Curtiss planes. And while on the subject of controls and sta- 

 bility, we should make it clear that it was in this area that the Wright 

 invention really counted so effectively. 



To begin with, the Wrights, and Spratt who aided them, made a 

 discovery in their early gliding experiments for which ample credit is 

 never given. They were definitely and distinctly the first ones in the 

 art, here or in Europe (and this included Lilienthal and, of course, 

 Langley), who found out and verified by test that the center of pres- 

 sure on a curved surface moves hachward when the angle of incidence 

 is decreased. All other experimenters had thought that the center of 

 pressure acted as it did on flat plates and moved forward. The 

 Wrights also verified this in their wind-tunnel experiments, and inci- 

 dentally Wilbur Wright mentions this in his famous paper before the 

 Western Society of Engineers in 1901. Center of pressure location 

 enters with fundamental importance into the question of stability, 

 because the knowledge of this enabled the Wrights to balance their 

 plane correctly and to arrange their longitudinal up-and-down con- 

 trol to operate properly. Then, of course, the basic Wright invention 

 on which they received their patent was their lateral control of roll. 

 They put into practice the realization that up-and-down control and 

 side-to-side control by rudder were not enough for successful flying, 

 and that a third control was needed to balance laterally in roll. 



The Wrights first incorporated lateral control in their airplanes 

 by the well-known lateral twisting or warping of the wings. When 

 they did this, of course, the side that had the greater angle of inci- 

 dence, and would therefore raise up, would at the same time have a 

 greater drag and therefore would require compensating rudder action. 

 This was where the Wrights combined the directional yaw and the 

 lateral-roll control into one movement, although in later types of other 

 constructors like Curtiss, pilots learned to do tliis as part of their train- 

 ing. As we progressed into the tractor type with a fuselage, the fuse- 



