PPRuNe Forums - View Single Post - Coriolis vs Conservation of Angular momentum
Old 21st Dec 2020, 16:51
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Vessbot
 
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Originally Posted by Robbo Jock
You've just hit the nail on the head. That is exactly why a gyroscope (or a spinning top or the Earth) behaves the way it does; it is a solid object, spinning - the force exerted on one particle is passed to all of them because they are all welded together. Apply a force at point x to a spinning disc/sphere/cylinder/whatever and it will be applied to all of the point masses and hence the resultant felt at point x plus 90 degrees because they're all welded together. Whirl a singular mass on a string, or your spacecraft in orbit, or a rotor blade and apply a force to it, it will be felt at the point that force is applied - there is nothing else to affect that force application. The plane of rotation may or may not change (depending on the force, the mass, the rotational speed) but the applied force will be felt at the point of application. That is the difference.


Careful you don't mix up two separate steps, when you say "is felt," for the two setups. In both single mass and solid disk, the force applied TO the body is at X. The force applied BY it (after travel time, for the single mass), is at X+90.

Originally Posted by [email protected]
When a gyro precesses, it takes its spin axis with it and, if you tried to restrain that spin axis somehow, it would create strong torques that could induce secondary precession effects.
Originally Posted by [email protected]

When a rotor flaps, the actual spin axis (rotor mast) doesn't move as the blades do - look at introducing a 20 kt head wind gust to a stationary helicopter on the ground, the disc flaps back but nothing else changes - can a gyro do this?


A rotor also takes the spin axis with it. ("Virtual axis," "tip path axis," "along disk axis"...) it is no longer aligned with the shaft axis. So I'm not seeing this as a difference.

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Originally Posted by [/color
[email protected];10951693]

The blades flapping is a result of aerodynamic forces induced by the change in pitch and AoA.

Is that coherent enough?


​​​​​All is coherent and true, but it doesn't answer the question for an "alternative" explanation. How is this not gyroscopic precession?

Also, when you find yourself explaining the most rudimentary thing that you'd tell to a day-one student, to someone who identified himself as having "worked on rotor analysis for many years" (that the pitch link controls AOA and lift, which is a force that moves the blade… really? Hold the phone while I write this down!) it should serve as a strong clue that there might be a miscommunication somewhere. A few posts ago (#83, "I think I solved it") I asked a question trying to suss this out, but it fell by the wayside. Again, do you think our position is that the force applied to the blade is something other than aerodynamic lift? Because NO ONE is saying this in the slightest!


Last edited by Vessbot; 21st Dec 2020 at 17:18.
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