If your plane flies and it flies straight, all the twisting force (T) doesn't matter because your propulsive force (rpm on the prop) is definitely greater. If your prop has the same mass as the plane, then ****etaboutit.

Question is, what happened to the feet?

If Torque is measured in ft/lbs and thrust is measured in lbs, what happened to the ft?

What do you mean about propulsive force? What do you mean about twisting force? To me, twisting force means torque measured by (HP(5252))/rpm). Propulsive force could mean the same thing since the engine is doing work. If you meant propulsive force made by the propeller, then it would be a different equation T=CsubT[(air density*rpm)^2*D^4). CsubT is the thrust coefficient of the prop.

Anyway....musings.