To: 212 Man
As Kyrillian stated those were the words of Mr. Paul Cantrell. Mr. Cantrell is also the author of a web site that is called Helicopter Frontiers. This web site is actually two web sites both of which are supported by Robinson Sales agents and/or training facilities that use Robinson Helicopters. Here is his complete statement about Gyroscopic Precession.
GYROSCOPIC PRECESSION
Gyroscopic precession is a phenomenon occurring in rotating bodies in which an applied force is manifested 90 degrees later in the direction of rotation from where the force was applied. Although precession is not a dominant force in rotary-wing aerodynamics, it must be reckoned with because turning rotor systems exhibit some of the characteristics of a gyro. This diagram shows how precession affects the rotor disk when force is applied at a given point:
A downward force applied to the disk at point A results in a downward change in disk attitude at point B. And upward force applied at Point C results in an upward change in disk attitude at point D.
Forces applied to a spinning rotor disk by control input or by wind gusts will react as follows:
"table at bottom of page 2-44"
This behavior explains some of the fundamental effects occurring during various helicopter maneuvers. For example, the helicopter behaves differently when rolling into a right turn than when rolling into a left turn. During roll into a left turn, the pilot will have to correct for a nose down tendency in order to maintain altitude. This correction is required because precession causes a nose down tendency and because the tilted disk produces less vertical lift to counteract gravity. Conversely, during a roll into a right turn, precession will cause a nose up tendency while the tilted disk will produce less vertical lift. Pilot input required to maintain altitude is significantly different during a right turn than during a left turn, because gyroscopic precession acts in opposite directions for each.
ME SPEAKING:
I think his statement about gyroscopic precession not being a major factor in helicopter aerodynamics is like saying that Bernoullis' theory is not a dominant force in aerodynamics but it must be reconed with when you design an airfoil. Without gyroscopic precession entering into the design concept of a helicopter then you and everybody on this thread would be in another line of work.
Here is another point. You may have read some of my previous posts where I referenced Mr. Cantrells words on these two sites. The main thrust of these web sites is in support of the Robinson design. This web site is full of a lot of very good pictures of helicopters and diagrams. Just prior to the section on gyroscopic precession Mr. Cantrell was discussing the Robinson rotorhead and compared it to a Bell rotorhead. At the completion of that part of the discussion the reader was directed to the section dealing with Gyroscopic precession. Instead of diagramming a Robinson swashplate, he used the Bell swashplate to illustrate precession (his words above) and in doing that, any one that read his words would believe that he was addressing a Robinson swashplate. If this is the way it is taught at Robinson schools then I can understand why there is so much animosity towards me when I discuss the infamous 18-degree offset.
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The Cat
[This message has been edited by Lu Zuckerman (edited 16 December 2000).]