PPRuNe Forums - View Single Post - Cyclics, Semantics and Teetering Rotors ~ A question
Old 22nd July 2003 | 02:14
  #24 (permalink)  
Dave_Jackson
 
Joined: Apr 2003
Posts: 1,635
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From: Vancouver, BC, Canada
crab,

This thread is an attempt, by a few interested people, to acquire a better understanding of some complex activities. I don't think anyone is questioning the accuracy of Nick's remarks. They are contributory and appreciated.

The phrase 'Aerodynamic Precession' is used by Gareth Padfield &/or Gordon Leishman, two very respected helicopter dynamists.


Sprocket,

I think that the results from gyroscopic precession and from aerodynamic precession are identical, when one is considering a 'basic' teetering rotor.

" a spinning solid disk in an ideal setting used to demonstrate precession will have a force at one particular point, applied to make the disk/wheel etc tilt."

OK, but, remember that this is a 'solid disk" [structurally rigid disk] and therefor "a force at one particular point" will be transmitted to all points on the disk. The amount transmitted to the various points is a trigonometric function of the azimuths and the moment arm. The amount of this force that is transmitted to each radii-azimuth is identical to the force of a blade element at the same radii-azimuth.

When the consideration turns to a more complex rotor, Gyroscopic precession start to 'fly out the window'. In fact, IMHO, is better to use Aerodynamic precession in all circumstances; with the possible exception of when considering the hub portion of an articulated rotor with a large flapping hinge offset.
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There is Rate cross-coupling, Acceleration cross-coupling and apparently a much less known coupling called Washed-out cross-coupling. I am guessing that Washed-out cross-coupling is associated with time and therefore the speed with which the cyclic stick is pushed forward etc. This seem to be inline with Nick's remarks and some information he provided in an earlier thread, where he mentioned that the flight controls on the Comanche could tailored to the specific flight situation.

If this is correct, then the relevance of Washed-out cross-coupling [Wee-wa] may or may not be important in a 'basic' teetering rotor
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