View Full Version : Strange phantom torque behaviour. Anyone else?

11-25-2005, 08:51 AM
Theres a strange characterstic going on here that I've reported to the bug team at 1C. If you fly a single engine a/c and turn off the motor, you'll find that if the prop windmills you'll get a very strong rotational force in the opposite direction to the direction of torque. I find this a bit suspect...

However, it gets worse.

For when the prop actually stops windmilling (whether jammed or low airspeed) suddenly that mysterious anti-torque force completely disappears, nay, REVERSES and you are suddenly forced to throw the stick around in counteraction.
It gets very tedious when deadstick gliding around the speed at which this change happens; its not always easy to prevent it especially if you're making quick adjustments to make it into a field...

"Hmm, a bit high here, I'll drop the nose and lose some of that alt," speed picks up, prop starts to windmill and *bang!*; sudden reversal in lateral stick force!

I'd post a track but don't know where to host it!

I first noticed it on the Spit IX - anyone had it on any others? If at all?

Just interested to find out!

11-25-2005, 09:15 AM
Yeah i get that, I first noticed it in the MkVIII spit.

11-25-2005, 10:01 AM
Originally posted by Arm_slinger:
Yeah i get that, I first noticed it in the MkVIII spit.

same thing on focke, I don't think that phenomena is limited to Spit

11-25-2005, 11:47 AM
The same in teh Bf109, out of fuel while landing and "phantom" torque swung me so brutally that I crashed...

11-25-2005, 12:37 PM
Many WW2 aircraft were trimmed via the structure (offset tails, wing twists, mostly subtle) to fly straight with cruise power. It might be that with the engine off it's the structural trim that is in effect. But perhaps it is too much?

11-25-2005, 01:18 PM
I think this phenomenon isn't totally in conflict with the laws of physics:
When the engine is running and has enough power, it exerts torque to the prop and then the prop exerts equal but opposite torque to the plane, which has to be cancelled by structural trimming.
When the engine is at very low power (braking) or windmilling, the prop spins the engine and thus exerts torque on the plane to another direction and structural trim strenghtens it.
So as long as the prob is spinning, the torque is OK.
But when the prop stops spinning completely that "braking" torque disappears and the plane has to be trimmed again to another direction. But I think this effect is too strong and the structural trim should still keep turning the plane to the same direction (opposite to the torque felt while increasing throttle).

I'm not sure if I'm right because airspeed and many other variables affect trimming and thus the situation is way more complex.
Anyway the most brutal and dangerous torgues act while engine rpm changes and these are due to accelerating or decelerating masses.

11-27-2005, 09:09 AM
Thanks guys...

Birdman, i was thinking along similar lines that this might be the cause, so windmilling prop understandable but to have such magnitudes of force reversal seems a little ..over-amplified...

11-27-2005, 09:37 AM
yes the plane becomes very hard to control, will suddenly roll in one direction all by itself, very quickly.

while triming is true, the effect should be gradual