Higher order harmonics
The ones I studied are induced due to aerodynamic differences and vortices.
For the flapping versus coning (see Daves remarks) I always presume that the hub is straithtend out by the dominant centrifugal forces.
For instance in a R22/R44 the second order harmonic is important (5-10%) at high speed, high coning, and flapping. These disturbances could temporary dis-align the head if flapping or coning friction were significant and coning would have more friction than flapping). I assume that they are not significant in the case of R22/R44.
During important transients (turbulence, wind gust) I guess some minor temporary (0,5 to 1,5 rev) unbalances could occur. (not calculated yet)
Delta3
Chiplight
This is what I wanted to stress, the first order simplified condition is not lift equilibrium but flapping moment equilibrium, see previous 3D rotor plots I published.
The physical equation at the foundation of rotor calculations is flapping moment equilibrium (not static but with inertia, coriolis etc).
In certain flight profiles the rotor is nicely running perpendicular to the mast
(blow back equal to forward cyclic, delta3 or other compesations schemes offsetting lateral effects) In that case there is no flapping, but there is an important aerodynamic force difference, and the rule is then that moments are equal, not lifts.
An important corollary in this simplified condition is that rotor trust will be laterally inclined to the backward blade (to the left in an R44) because of coning, so the total lift is not perpendicular to the tip path.
Delta3
Last edited by delta3; 13th Apr 2005 at 22:30.