Hi heedm:
Gyroscopic precession or aerodynamic precession or both?
From ~ Helicopter Flight Dynamics: The Theory and Application of Flying Qualities and Simulation Modeling ~ 1996 ~ by Gareth D. Padfield.
The phase angle "
stems from the two components ...... one aerodynamic due to the distribution of airloads from the angular motion, the other from the gyroscopic flapping motion."
I am certainly not qualified to question Gareth Padfield, but what the heck, this is the Internet and anything goes. As mentioned before, since a rotor's mass and RRPM (excluding minor adjustments) are constants. it is possible to consider his reference to "gyroscopic flapping motion" from an aerodynamic perspective.
Nick has mentioned that the optimum phase angle for a specific helicopter will vary as the flight aerodynamics change. This is also reinforced by the Sikorsky ABC and its widely variable Gamma.
Virtually all the inputs are aerodynamic, even a non-rotor input such as parasitic drag is aerodynamic. Trim, stability and control are looked at primarily from an aerodynamic perspective.
To me, it appears that an aerodynamic perspective, where possible, is the preferred method.
=======
Having concluded the aerodynamic sales pitch; lets talk rotational physics.
=======
>"
My point is that when you make everything unearthly rigid, you have turned the helicopter into a gyroscope. "<
Only the rotor is a gyroscope; in the horizontal plane
The whole helicopter is *starting* to become a gyroscope in the vertical-longitudinal plane, but, this will only last until the desired nose-down pitch is achieved. Then all precessions stop.
>"
You apply the upwards force to the tail, a moment is created, angular momenta are summed, and the helicopter rolls a very small amount to the left. "<
The very small roll to the left can be also explained aerodynamically and the change in pitch is exactly what we commanded. In a very rigid coaxial or intermeshing helicopter, the tendency for a small roll to the left will be offset by a tendency for an equal roll to the right. These combined tendencies should slightly decrease the helicopters roll and pitch rate thereby, adding to its stability. I hope.
