To: Dave Jackson. .. .“I agree that on teetering rotors, the two blades, basically, lead-lag in unison. The small amount of lack of unison is handled by a strong hub and flexible mast. The undersling is probably an attempt to keep the rotor's mass centralized when the disk tips”.. .. .Response:. .. .On an underslung rotorhead such as that used on a Bell the tendency to lead and lag is minimal because of the underslinging of the head. When the blades teeter the axis of rotation intersects the axis of drive. On a conventional articulated rotor system the axis of rotation deviates from the axis of drive causing leading and lagging to take place. All of this was covered in several other threads. The Robinson rotorhead like the Bell can teeter and it too is underslung. However the blades are free to flap and in doing so the two axes deviate from each other and leading and lagging takes place. But, the blades can’t actually move so the loads are reacted by the cone hinges, the pitch change bearings, the teeter hinge and the rotor mast as well as the blade itself. The tendency to lead and lag can be verified by the inspection of the cone and teeter hinges as they are worn in an elliptical pattern.. .. .“The R-22 aerodynamic center is probably at 25-27% chord but it has been mentioned that the attachment point is at 40-45% chord”.. .. .Response:. .. .If what you say is true then the spanwise bending would be excessive. In an ideal design the pitch change axis, the aerodynamic center and the chordwise CG should all be on the same point. That is why on larger blades the tip weights can be adjusted in order to get them as close as possible. Since it is not possible to get the three points coincident with each other the blades or the blade attachment is designed to react these loads and the loads then go into the rotor head. . . . .. .“The R-22 hub's blade-feathering axis is 0,28" ahead of the mast's center of rotation; to reduce the moment carried by the pitch change bearings”.. .. .Response: . .. .This is what I stated above in my first post. Spanwise bending causes the moment you alluded to. This displacement of the rotor blade relative to the mast centerline is designed into the system because the chordwise CG of the blade is shifted relative to the mast centerline thus minimizing the spanwise bending.. . . . <small>[ 04 March 2002, 02:48: Message edited by: Lu Zuckerman ]</small>