Hello all,
I've been reading this thread for a while and would like to add a bit.
Lu, I think Try_Cyclic has the idea, dynamic rotors do not react simply like the blade angle. On certain systems the behavior of the stationary blades is not the same as the behavior of the rotating rotorhead. The phase lag is defined by
delta(phi) = 90° - arctan((nu^2-1)/(gamma/8))
where nu is the dimensionless natural frequency of the rotating rotor, and gamma is the Lock number, which defines the ratio of aerodynamic to inertial forces on the rotor blade.
For a simple articulated rotor with no root spring, nu=1, meaning the natural frequency of the rotor is 1/rev and the phase lag is just defined by the first term of the equation, 90°. This seems to be the case on almost all fully-articulated rotors and many teetering rotors like the 206. But if either a spring is introduced at the root, such as in many modern hingeless rotors, or (I assume), as pitch-flap coupling is introduced, nu becomes slightly greater than 1 and the phase response of the rotor is reduced. Hence, a hingless rotor is quicker to respond, and the phase lag between control input and the rotor disc motion is less than 90°.
Whether this is the case for the R-22 and R-44 I am not sure, but if I understand Try_Cyclic, he is saying that the delta hinge is reducing the phase lag to less than 90, possibly 72°.
As others have echoed, I await the official response from Mr. Robinson.
- Kyrilian
P.S. If interested, formulae above come from 'Helicopter Theory' by W. Johnson, pp 225