The following is submitted to provoke interest, boredom, or a scathing rebuttal.
[list=a][*]For a rotor that is freely articulated at the center of rotation, or a teetering rotor, the phase lag is 90-degrees.[*] For rotor that is totally rigid , except for feathering, the phase lag is
0-degrees.[/list=a]
The conditions are;
The rotation is CCW, when viewed from above.
Azimuth-0 is aft, azimuth-90 is to the right, etc.
The flight maneuver is a transition from hover to forward flight.
In the case of A/, the higher blade pitches will be found between azimuth-181 and azimuth-359, with the highest at azimuth-270. The 90-degree phase-lag will result in the disk being high between azimuth-271 and azimuth-89, with the highest at azimuth-360. This will cause the rotor disk to
'drag' the helicopter's nose down about its pitch axis.
In the case of B/, the higher blade pitches will be found between azimuth-271 and azimuth-89, with the highest at azimuth-360. The zero-degree phase-lag, in conjunction with the absolutely rigid coupling of the rotor to the fuselage will cause the rotor disk to
'pry' the helicopter's nose down about its pitch axis.
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An addendum to the forgoing is that this extremely rigid rotor must have higher than normal strength and thus greater mass. The mass will invoke gyroscopic precession.
. However, the gyroscopic precession will be relatively small, and in the case of twin counter-rotating main rotors, such as the coaxial and intermeshing configurations, the opposing gyroscopic precessions should provide some stability.
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That's the story and I'm sticking with it; until a knowable person says that parts of it, or all of it, are BS.
[ 25 November 2001: Message edited by: Dave Jackson ]