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Physics
Classical Physics
Off center torque applied to a rotating body
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[QUOTE="jbriggs444, post: 6652283, member: 422467"] It is difficult to discern what you are asking about here. When you talk about the engines having "momentum vectors", you presumably mean that they have "angular momentum vectors". Or, in particular, that the spinning turbine shaft and blades has a non-trivial amount of angular momentum. So we have the rudder applying a torque to the plane. The plane yaws in response. A turn to the right or left within the plane of the craft-relative horizontal is called a "yaw". As opposed to a "roll" or a "pitch". The yaw rate (so many degrees per second) will result in a rate of change in the angular momentum of the spinning turbines. This would tend to cause the spinning turbines to precess. They will tend to either pitch up or pitch down depending on the direction of the turn and the turbine's direction of rotation. The engine bearings that hold the turbines in place will naturally deal with this pitching effect, applying a counter-torque that prevents the turbine shaft from pitching up or pitching down. The effect of that counter-torque is to cause the turbines to precess so that they continue to match the orientation of the aircraft as a whole. It is not that much torque. The bearings can deal with it. Obviously they can. Because they do. If the pilot has to crank in a tiny bit of elevator (the horizontal control surfaces on the tail) to compensate for the up or down pitching torque from the engines, he will do that automatically and without even thinking about it. "Plane pitching a bit down -- I'd better pull back slightly on the stick" If the angular momentum in the engines were all that big of a deal, one would expect to see aircraft doing cartwheels on the tarmac every time they throttled up their engines. We do not see that. We do not see the aircraft tilt at all when throttling up. At least I sure do not. Edit: I have not been able to Google up very much with respect to engine specifications for moment of inertia and rotation rate. However, there is some interesting reading out there. Your typical "jet engine" is actually a turbofan. With the turbine engine running a shrouded fan at a lower rotation rate, lower exhaust velocity and higher mass flow rate compared to the engine itself. This is a big win for fuel efficiency. Here, the concern about moment of inertia is apparently centered on how fast one can spool the engine up, rather than on how rapidly the engine bearings can force it to precess... [/QUOTE]
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Off center torque applied to a rotating body
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