This space reserved. I have to go to a medical appointment. When I return I will respond.
I just got back. Much of what I was going to say was said in the next post however the below listed paragraph taken from that post is not correct.
“When the rotor disc is tilted by blade flapping, the two athwartship blades, in order to maintain a constant velocity in the plane of rotation, must move on their drag hinges to the position shown. If drag hinges were not fitted, the blades would be forced to accelerate and decelerate with every revolution”.
It states that if drag hinges were not fitted the blades would accelerate and decelerate with every revolution. The blades do in fact accelerate and decelerate with every revolution. That is called leading and lagging. What the author of the quoted article should have said was this. If the drag hinges were not fitted the mechanical forces would cause the blades to bend spanwise moving forward and backward at the tip with the bending taking place throughout the length of the blade. This is what happens on a rigid rotor system such as that used on the BO 105 and BK117 as well as others that do not have lag hinges. It even happens on Bell Helicopters but the bending is limited by the underslinging of the rotorhead.
The term Hooke’s joint effect is not a good description of what is happening. The technical term is Conservation of Angular Momentum. Also, it should be noted that the advancing blade leads and the retreating blade lags. Another incorrect point made by the author is that the blades are 90-degrees apart during hover. (Assuming a four-blade system). This would indicate that in hover the blades form a cross. This is not true. The blades because of their inertia hang back slightly from the pure radial position. All leading and lagging takes place behind the radial position and, the only time the blades are ahead of the radial position is when you are autorotating or, applying the rotor brake.
[This message has been edited by Lu Zuckerman (edited 21 June 2001).]