Originally Posted by
Reely340
There is a nice vid about the Huey the Nelson-D'Anona foundation is operating.
https://www.youtube.com/watch?v=zunO6iUVUT0
...
I could understand if there would exist a specific rpm where the system and its dampeners enter resonance,
but then slightly off that rpm everything should be rock solid.
Given the structural stress rotational imbalance such a heavy rotorsystem would cause,
I presume the Huey would have some rather tight balancing limits to be cleared as airworthy, not?
Once the rotor is out of a pure hover and has edgewise airflow, there are significant harmonic air loads on each blade. 1 per rev, 2 per rev, 3 per rev and so forth. These forces variously sum or negate themselves at the rotor hub and transmit certain frequencies to the fixed system. 2 per rev vertical blade loads sum to a 2P vertical airframe vibration while 1P and 3P horizontal forces in the blades sum to a 2P horizontal vibration in the airframe. Higher frequency harmonic air loads also sum, but the magnitude of the forces generally drop as the “per rev” increases, unless the blades themselves are poorly tuned and get excited near a resonance.
The 1P and 2P harmonic air loads in a rotor are large enough, that even a very well tuned structure sees large loads without a hinge in the relevant direction, but of course, hinges introduce some new problems, particularly hinges in the rotor plane.