To: SIKORSKY
The theory books explains, that the retreating blade flaps down
The only time the retreating blade flaps down is in a blowback / flapback condition or in a retreating blade stall condition.
Many years ago Sikorsky placed a camera on a rotorhead mounted on a whirl stand and one of the things they discovered was that the advancing blade led and the retreating blade lagged. Up until that time it was assumed that the opposite was true.
On a four blade fully articulated rotor system that was viewed from above the blades would be arranged like a peace sign with the forward blade and aft blade in alignment with each other and the advancing blade forward of its radial axis and the retreating blade aft of its’ radial axis. This is an example as there are other factors influencing blade position two of which are drag and inertia.
Duck for incoming (read Nick Lappos)
