To: Baque Flip
Regarding the second paragraph of your post about gyroscopic characteristics. The rotor disc like the rotor on a gyroscope have two things in common. One, is rigidity in space. In other words, it will stay in the position you put it. The other is precession, as it will move to where you command it. In order to make the gyro/rotor disc move from its' rigid in plane position you have to input an external force. In the lab or in training school the instructor will demonstrate these characteristics using a multi gimbal gyroscope. With the rotor spinning, the instructor will perturb the rigid rotor by applying a force to the outer gimbal ring. The results of that force input causes the rotor to tilt in the direction of the force but 90-degrees later in the direction of rotation.
In the case of the rotor system it is either a direct force on the swashplate in the case of a Robinson or by a hydraulic servo such as those used on larger helicopters. The precession is still the same, 90-degrees and the precession will continue until one of two things happens, 1) the force stops or, 2) the control system or the rotor system comes up hard on the stops. In the case of 2 above the pilot becomes aware of the problem immediately as there is a very large vibratory force applied to the airframe from the rotorhead.
What you stated in the last sentence of your post discounts precession and states that the rotor moves because the swashplate position changes the pitch on the blades and the disc moves as a result. The change in pitch due to swashplate movement is the external perturbing force. The change in pitch creates a force differential across the disc, which results in precession.
Regarding the massive pitch couple on the Lynx when the AFCS is turned off I would direct you to read my post on the Piaseki Compound Helicopter where I made a comment about the Cheyenne helicopter.
The Cheyenne because of the design and the stiffness of the blades had a constantly changing phase angle (90 + or,- 5-10 degrees of precession). This little problem killed one pilot and destroyed a very large and very important wind tunnel in California. It took two years to figure out how to solve the problem. What they did was to measure and monitor cyclic stick position and when the blades went where they wanted instead of where the pilot commanded them the computer would sense this and command the servo system to instantly compensate. Say, the pilot pushed the stick forward and the disc tilted to the left, the computer would alter the servo input as if the pilot moved the cyclic to the right. The system worked very well but it was so complex and contained many single point catastrophic failure modes that the Army cancelled the program. I would assume that the AFCS system does the same on the Lynx as the flight computer did on the Cheyenne. Its’ too bad they can’t put one on a Robinson R22/44.
This principle of external force causing a gyro to precess is used in electro mechanical and air driven gyro instruments on the instrument panel of your ride. Only in this case it is the movement of the aircraft around the instrument that provides the perturbing force and the movement of the rotor is connected to the indicating needle or the ball on the gyro horizon.
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The Cat
[This message has been edited by Lu Zuckerman (edited 20 December 2000).]
[This message has been edited by Lu Zuckerman (edited 20 December 2000).]