I'm with Baque Flip on this one. The precessive qualities of a gyro stem from the inertial effects of the rotating mass. As has already been said the mass and rpm of a rotor are not sufficient. I once had a formula for the minimum mass/rpm for a gyro which I have (thankfully for most of you) misplaced, but I did use it on a helo rotor system (Lynx [grey]) and fell well short. Incidently it is inertial effects that cock up the phase lag in an offset flapping hinge.
[This message has been edited by Grey Area (edited 21 December 2000).]