Hmmm...Lu, what do you think of this?
It looks like most rotorhead designs have purely vertical pitch links, although some tilt out (from swashplate to pitch horn) and some tilt in. However I don't see any rotorhead designs where the upper (pitch horn) and lower (swashplate) ball joints are out of phase with each other. Is this an issue with centrifugal forces with a spinning rotorhead, and would this cause unwanted pitch changes?
Grainger, it's both the combination of the location of the flapping hinge (and its center of axis) and the LENGTH of the pitch horn (thus effecting the distance of the ball joint attachment point from the blade center line) that establishes the phase angle of 72 degrees. If the pitch horn was shorter, the phase angle would be less than 72 degrees, but if longer, then the phase angle would be more than 72 degrees (and approaching 90 degrees if the pitch horn was say 15 feet long). That's simple trig. FWIW, the Robbie rotor blades do have rather long pitch horns.
I wish I had a good textbook on helicopter design, I'm sure these issues would be covered.
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Safe flying to you...
[This message has been edited by Flight Safety (edited 29 June 2001).]