A precession is a motion that spinning masses do where the axis of the spin traces a cone. Stick a flashlight pointing upwards on a moving turntable that is mounted horizontally. If the flashlight makes a dot on the ceiling then there is no precession. If you then pick up the turntable and keep tilting it so that the flashlight traces a circle on the ceiling, then you have precession.
Helicopter rotors, in the simple case, do not exhibit any such behaviour. In the full analysis, even a simple spinning top has at least two frequencies/amplitudes of precession. So I imagine a helicopter's rotors would show many of these.
Gyroscopic precession occurs when a force acts continuously on a spinning object at an angle to the spinning axis. Like when a spinning top starts to lean over, gravity pulls down on the object causing the top to precess. This can be shown quite easily in the classroom. It can then be broken down in the classroom to show that it's caused by a force acting on a rotating object apparently being realized 90 degrees later in the rotation.
Because it's easy to show in the classroom, it's also an easy way of convincing prospective helicopter pilots that a control system that appears to be rigged 90 degrees out of sync will actually work.
If you agree with me to this point, we'll all have to agree that gyroscopic precession is a big lie told to make life easy.
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I haven't read Padfield's or Leishman's books yet, so I still don't know what aerodynamic precession really is. If it's an attempt to explain why the controls are approximately 90 degrees out of sync, then I'd question if they even used the word precession accurately.
However, if they are referring to some higher order response of the rotor system, then they may in fact be using the term accurately.
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Dave, "stirring the cyclic" is a term for overcontrolling. Lots of students do it. They get task saturated trying to hover, end up moving the cyclic all over the place which means more effort required in controlling yaw & power. Also bad when operating close to power limits since it results in your total thrust vector leaning from the vertical and time averaging to a shorter but vertical vector.
Matthew.