[email protected],
I don't have a gyroscopic precession theory, but I am standing on the shoulders of the giants from the collective work of over 300 years of classical mechanics. If that's not holding true in helicopters, then we need to find an Einstein to put us straight about what's actually happening.
I agree entirely that aerodynamic forces impose the couple, and they need the hinges; saying change the direction of angular momentum is just a complementary way of saying what you're saying.
That's exactly what you have in the controls - a mechanism to ensure that the blade flies in a way that alters its motion in the desired direction. That comes from an aerodynamic force, but where does it act? To tilt the disk down at the front and up at the back, where are the maximum and minimum lifting sections of the disk? To the left and right or to fore and aft?
All we would need is a hydraulic ram to exert a linear force 90 degrees before the desired blade position, give it a poke or pull and let precession do the rest.
If you were to do that you would get just such a motion. Twist a portable fan or a large circular saw in your hands to watch it at work. But the moment you are required to impose for rapid motion is large. In a helicopter that large force comes from the airflow on the blades not from the hub, but it's still there.
We should drop "gyroscope", as it too vividly conjures pictures of a spinning top toy, but I claim that the angular momentum of the rotor remains an important, defining property. If it wasn't, then you could roll or pitch the machine as fast in rpm as you can yaw it, and I don't believe that's nearly the case.