John D. wrote:
One aspect of the V-22 vs single rotored helicopters in VRS to ponder is why the V-22 apparently "rolls off" and cannot be controlled, whereas the single rotored vehicle remains controllable in VRS.
Apologies if this has been posted already, but here is Prouty's take:
For a tilt-rotor aircraft in the helicopter mode, we could make the same scenario for descent in the vortex ring state if both rotors were acting the same. It is probable, however, that they will not act the same because of thrust fluctuations that are always associated with the vortex ring state. If, for some reason, a small roll to the right starts, the right rotor drops, its descent angle increases and it loses thrust in the process. The left rotor, on the other hand, rises and regains some of the thrust that it had lost. This is another unstable situation in which the roll rate will just keep increasing in a divergent manner unless the pilot stops it with his roll control. But since the situation is unstable, he might go into a divergent left roll. It can be represented by a one-degree-of-freedom system with negative damping — a very difficult situation to control!
Rotor & Wing Magazine :: Ask Ray Prouty