Originally Posted by
Lonewolf_50
If the main rotor blades are stalled ... NO lift and so I infer no torque reaction to the body (edit: though certainly some precession due to mass and inertia) ... but the finestron is still turning (be it with a lot of pitch or a little pitch, control position dependent) then I'd expect there to a value of thrust, however modest, whenever that set of blades is spinning until they too either
1. stall
or
2. the lack of V gets down to a low enough value that V^2 isnt big enough to matter.
First of all a small amendment regarding torque:
The question of torque on the airframe does not necessarily depend on Lift. Any kind of drag applied to the rotor will create torque as long as the engines are creating torque.
This drag can either come from producing Lift or from being stalled.
So the only question relevant for the torque on the airframe will be if the engines were operating at anything above idle or even being shut down.
Regarding effectivesness of the Fenestron at RPM whre the main rotor is stalled: That is a good question.
My personal feeling is that it will continue to create lift/yaw significantly beyond the critical RPM for the main rotor. The high number of blades and small spacing between them will cause downwash from one blade interfering with the next blade thereby decreasing local AoA. Additionally the blades of the Fenestron have a rather large camber also improving behaviour at high AoA.
Therefore I tend to believe that it will create meaningful yaw/torque probably down to quite low RPM's.
So if the engines were shut down and stalled it will depend on the position of the pitch change links (pedals) if the helicopter will start spinning significantly pro Fenestron or not. Friction in the main rotor drive will compound to this yaw.