THE AUTOQIRO PITCAIRN 267 



The accident caused Ciervii to review the entire progress of 

 mechanical fliglit. He reasoned that if a proven, ellicient airphme 

 couhl be crashed so easily by a seasoned pilot's Hying it slowly near 

 the ground, there was something fundamentally wrong with the 

 airplane. He canvassed the entire field of flight by heavier-than-air 

 craft in the search for a fundamentally safe Hying machine. Finally, 

 after continuous research in theory and practice, he struck upon the 

 idea of autogiration. 



While there are nnvny ft)rms of autogiration, but one seemed prac- 

 tical to the great inventor. This was the result of extraordinarily 

 sound and inspii-ed engineering tleveloped from higher mathematics. 

 The Autogiro would have been impossible without the preliminary 

 development of the correct theory. 



On his first machine he used two 4-blade rotors. One of these was 

 placed above the other, with the two rotating in opposite directions. 

 He had realized that the lift on the blades while traveling with the 

 flight path would be much greater than while going against it, and 

 the idea of the two rotors with opposite directional rotation was 

 calculated to cancel out the tendency to tip over. He found that the 

 upper rotor turned much the faster, however, and the tendency to 

 tip over was so strong that no real attempt was made to take it off 

 the ground. This was Cierva's only attempt to use two rotors on 

 the same machine. 



His confidence was undiminished, and he set to work on the second 

 type. It should be mentioned here that, although probably in excess 

 of 50 or GO Autogiros have been constructed, there have been only 

 6 or 8 general types, and that many models were simply slight modi- 

 fications of their predecessors. The rotor of the second type em- 

 ployed three rigid cantilever blades. He attempted to compensate 

 for the difference in lift between the blades while advancing and 

 while receding by a mechanism which changed the angle of incidence 

 of each as it revolved, giving the greater angle on the receding blade. 

 This mechanism proved cumbersome and substantially ineffective. 



On the third general type, which like the others was constructed 

 around an airplane fuselage, he used five blades, and — it flew. The 

 tendency to tip over was corrected with ailerons. Althougli it flew 

 but a few feet, he told me that no other machine has ever given him 

 the thrill that he experienced when this proved that an Autogiro 

 could be flown. The machine of course had many deficiencies, chief 

 among which was that of the strong gyroscopic force set up by tlie 

 rotation of the large rigid rotor. The gyroscopic force was so strong 

 that the controls of the machine had to be greatly modified. 



Encouraged by its flight success, however, he built a model which 

 embodied one of the main principles essential to a successful Auto- 

 giro. In this he constructed the spars of the blades with rattan. 



