bifilar vibrations 3P

[saksmito]

Hi.
I´ve began to work on the Sikorsky S76 just a couple of months ago and have a question.
Where could I find info about bifilar vibrations and the way the S76 dampens them.
I´ve seen in the configuration that it has a damper consisting of four masses with an excentrical movement. The problem is that this kind of vibration is absolutely new for me. My experience is with the Superpuma model from Eurocopter, and the only vibrations there where the ones from tail and main rotors. Don´t know how does it appear nor the mechanism to reduce it.

Thanks.

 

[Intermesher]

This thread may be of value.

http://www.pprune.org/forums/archive/index.php/t-183289.html

 

[saksmito]

Thanks a lot for your response. It´s been very useful.
Anyway I still have a question not answered in that forum (better said answered but not understood).
As it seems when the blade makes it´s way through the air it passes from bearing more to less weight in one roll.
Multiplied by the number of blades makes it normal to have n excitement cycles in one roll (or at least an armonical number)
So... why do the dampers work on n+1/n-1?