OK, I understand now. You're talking about the torque reaction of the tail rotor. I'm talking about the precession torque caused when the tail rotor is yawing. And you're right: I didn't consider changes in tail rotor torque reaction. This will occur since the tail rotor pitch did get a step input to induce the yaw.

In my case, I gave a right rudder input, which would reduce the tail rotor torque, which would have caused a nose-up pitch. This happens to be the same direction as the turbine precession pitch moment caused by precession. So I don't really know what I was seeing - except that it didn't appear to be a whole lot different to my piston powered 60s.

Quote:

Phil, I think were both saying the same thing but were using different language to describe it. I'm getting confused when you use the term precession torque, and in my mind thats those are two different forces. Torque Tendency (like the main rotor applying force to the heli causing it to yaw about the vertical axis in the direction of travel) and Gyroscopic Precession where a force applied to any spinning object will cause an interaction 90degrees in advance of the direction of travel, and parallel to the original forces vector.

Assuming were on the same page (I think!), I still dont see how a turbine could act with sufficient force to prevent the full mobility of the heli.

I didn't think the turbine would have enough angular momentum to cause problems either. However if you look through the forums, you'll see conjectures that it would.

If I knew the mass and dimensions of the rotating parts in an HP5 I could estimate the moment of inertia and know for sure that precession from the turbine is not significant. A least I could see how it compares with the torque reaction from the tail rotor.