To:Rotorque, Helisphere and 212man
This might get a bit mixed up because intermixed with your comments about corriolis forces you were addressing static droop.
One of you made a comment about leading of the blades when you pulled collective in countering a statement I had made about a diagram. Whoever made that statement was correct. The leading would be limited and controlled by the amount of blade cone. If the blades were returned to flat pitch the lead would diminish to the point that the blades were in the normal position. It would be assumed that the blades in the flat pitch condition would be in the pure radial position and assuming a four-blade system the blades would form a cross. In actuality, due to the inertia of the blades instead of the blades forming a cross it would be more like a very mild X and as such the blades all would lag behind the pure radial position (Cross) and all leading and lagging would be behind the radial position. The only time the blades ever cross the radial position is during auto rotation when the blades are driving the system as opposed to the other way around.
Regarding the leading of the blades causing the rotor system to speed up (for a very short time) I don’t think this is true. Because the blades are mounted on a hinge and connected to the rotor head by a soft damper any movement of the blades about the lag hinge would not be reflected on the rotorhead. That is, unless the rotor system is in autorotation when the dampers are bottomed out and the aerodynamic forces on the rotorhead are back driving the gearbox.
If what was said above were true then the leading and lagging of the blades would be reflected in the dynamic system and the power train and be very noticeable by the pilot. The only time the pilot is aware of this condition is when he has a bad damper and he feels it as a lateral beat. But although the lateral beat stems from leading and lagging it really is a mass balance problem as the effected blade is out of balance with the other blades relative to their respective positions during rotation
Regarding the terms flapping up and flapping down there is a problem of interpretation. These terms are usually discussed in teaching helicopter aerodynamics and it causes many many problems. It is true on a two bladed rotor system if one blade flaps up the other will flap down. Assuming you are in a hover in a Bell and discounting any cyclic adjustments for tail rotor translation here is what happens. In a hover the blades are disposed at 90-degrees to the rotor shaft. When the pilot pushes forward the aerodynamic and precessional forces will cause the disc to dip down over the nose and rise up over the tail. In order to do this the advancing blade must flap down over the nose and due to the construction of the system the other blade flaps up over the tail. Now to what you were referring to. The advancing blade meets the oncoming relative wind and flaps up and the other blade flaps down. When the rotor system flaps relative to the fixed swashplate there is pitch coupling and this restores the blades to the commanded position therefore any tendency to flap out of the commanded disc position the blades immediately return. However when they use the flap up/flap down illustration they never address pitch coupling.
Regarding the comment about seeing the blades flap up on the advancing side and flapping down on the retreating side of an S-61, I would advise you to look at the tip path change when you move the cyclic. The disc will tip down in the direction of cyclic movement and, although you can’t see the rear of the disc I will assure you if one part goes down the opposite side of the disc will go up. Even on a 7 bladed CH-53.
In one post I mentioned Hookes joint effect in agreeing with a post made previously. On a hooks joint there is not a constant velocity in the rotation of the input Vs the output and that is when I mentioned a constant velocity joint being employed on a front drive automobile as opposed to using a Hookes joint in the drive system. The leading and lagging is a function of the law of conservation of angular momentum or as it is known as Corriolis forces. To minimize the effects of Corriolis forces on a single rotor helicopter they underselling the rotor system to lower the center of mass relative to the drive point on the rotor shaft. Speaking of center of mass, the center of mass on the blades does not move in or out relative to the root or tip of the blade. However it can move up or down relative to the flapping hinge and this is what causes the Coriollis force to kick in. The mass of the blades increases due to centrifugal force and does two things it increases the stiffness of the blade and it increases the moment of inertia of the disc system providing the forces necessary to cause precession when a perturbing force is appplied.
Now lets discuss the exceptions to the statements above. I previously stated that with a soft inplane rotor system the leading and lagging forces are not transmitted to the rotorhead and then into the drive system. A major exception to this is the Robinson head. The Robinson head has cone hinges, which are in effect, offset hinges that allow flapping in relation to the rotorhead itself. As I stated previously when a blade flaps it leads and lags. The Robinson head does not provide for leading and lagging brought about by flapping. Nevertheless, the tendency to lead and lag is there. These forces are so great that any lead lag motion is reacted by the cone hinges and then into the teeter hinge and then into the drive shaft and transmission. This fact is borne out by the high replacement frequencies for the respective hinges/bushings as they are worn into an egg shape. The Robinson head like the Bell head is underslung to minimize the tendency to lead and lag but the Robinson head unlike the bell head has the ability to flap and the Bell doesn’t.
Hopefully, I have covered all of the points in your respective posts. If not let me know as I am not going anywhere.
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The Cat