Originally Posted by
AF330
...
Am I right now?*Thanks
No, you sound mixed up. Let me try and sort this out.
...So momentum = Mass*Velocity...
Yep.
...Momentum is always constant...
Not necessarily, unless someone told you to assume that for their particular teaching example. It's possible in the case of props and gyros as teaching tools, but actually not true in real life most of the time. Angular momentum is not always conserved in real life.
But let's back up a bit and start simple first. For now, we can assume the speed of a bicycle wheel or a prop is constant, and there is no friction or other acceleration acting on it.
...Angular momentum = Mass*Velocity of a rotating object...
Yes.
...It is always equal....
Not if it changes. But like I said, we can assume it is constant in the case of a bicycle wheel or prop disc for now as a learning assumption.
...When we pitch up, we create a torque so we tend to make the prop rotate...
Not sure what you mean "make the prop rotate". Assuming we are using props as our example, here's how it goes.
1. A prop is fully spun up to begin with on a running engine. Turning at say 2400 rpm. This is constant speed, no change at any time for that.
2. A torque is applied in the form of a pitch input when the pilot raises the tail of the airplane using their stick. The torque is "seen" or felt on the prop disc at the top and the bottom. Actually it is applied though the engine drive shaft, but it does not matter how it is applied.
3. The airplane (prop disc etc.) responds with a left yaw. This is your gyroscopic precession.
Does this help?
... ---> we change the velocity of the prop so the angular momentum. The prop tries to keep a constant velocity (mass won't change) and creates a yaw turn...
You're reaching beyond where I think you should for now. I would not try and reach too far here by getting into conservation of momentum or anything that deep right now. All you need to know is how gyroscopic precession acts- a prop acts a like a big gyroscope and when it is already spun up to a normal running speed and torque is then applied to it via pitch input, it will react in another plane than the one in which the pitch torque is applied. Simple stuff- specifically, the plane of reaction is always 90 degrees to the upstream side on the disc or gyro where the original torque was applied. In this case the prop-gyro turns pitch torque into yaw torque. Are we ok now? I want to make sure we have that much before we get into it any deeper.