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# Rotor dynamics problem

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## Rotor dynamics problem

(OP)
I'm trying to get a clearer understanding about the use of Delta3 in a teetering main rotor, and any help will be appreciated.
__________________

When a 2-bladed rotor teeters (flaps) there is an acceleration and deceleration twice per revolution, due to a cyclic Coriolis effect.  On an intermeshing helicopter, the blades of the two rotors are at 90-degrees to each other, and this oscillation must be even more pronounced.

'Delta3 by Flap Hinge Geometry' [sketch ~ http://www.unicopter.com/0941.html] is incorporated in the Kaman intermeshing helicopters.  This specific type of Delta3 has a Flap-Lead coupling, which is in addition to the normal Pitch-Flap coupling.

I initially assumed that the Flap-Lead coupling was implemented to 'absorb' the oscillations caused by this cyclic Coriolis.  It now appears, to me at least, that the two oscillations are out of phase with each other by 45-degrees [graph ~ http://www.unicopter.com/0433.html#Graph].  This would imply that the delta3 is not achieving the assumed objective.

Any comments or correction of this assumption will be much appreciated.

### RE: Rotor dynamics problem

With reference to your rigid rotor, as I understand it, the rotor itself will generate vibrations at higher rotor orders, corresponding to the number of blades. If you are interested I have a solution to the issue of track and balance, which operates on exactly this theory. If you have an RTB algorithm which balances and trims out the N/rev harmonics, then a flat track is usually produced. Flat track as you will be aware does not necessarily mean low vibration, and vice-versa.

### RE: Rotor dynamics problem

(OP)
aerovibe,

Yes, I would appreciate hearing more about your solution to the issue of track and balance.

Thanks.

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