text: If the blade angles of attack on both advanc- 
  ing and retreating blades remained the same 
  the higher velocity on 
  as in hovering flight, 
  the advancing blade would cause a dissym- 
  metry of lift and the helicopter would tend to 
  It was this effect that created 
  roll to the left. 
  great difficu!ty during many early helicopter 
  and autogiro projects. Juan De La Cierva was 
  the first to realize what caused this effect and 
  he solved the problem by mounting his auto- 
  giro blades individually on flapping hinges, 
  thus allowing a flapping action to automati- 
  that re- 
  cally correct the dissymmetry of lift 
  sulted from forward flight. This is the method 
  still used in an articulated rotor system today. 
  The see-saw, or semi-rigid, rotor corrects the 
  lift dissymmetry by rocking the entire hub and 
  blades about a gimbal joint, By rocking the 
  entire rotor system forward, 
  the angle of at- 
  tack on the advancing blade is reduced and 
  the angle of attack on the retreating blade is 
  increased. The rigid rotor must produce cyclic 
  variation of the blade pitch mechanically as 
  the blade rotates to eliminate the lift dissym- 
  metry. 
  Irrespective of the method used to 
  correct the dissymmetry of lift, 
  identical aero- 
  dynamic characteristics result. Thus, what is 