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Dual Rotor Control Methods

Dual Rotor Control Methods

Dual Rotor Control Methods

(OP)
Greetings. This is my first post here so allow me to tell a bit about myself. I completed my Masters in mechanical engineering about 20 years ago. My thesis work was investigating the effects of tip vanes on helicopter rotors in hovering. However, after graduating, I've never worked with helicopters again though my interest has stayed strong.

That being said, could someone summarize how dual rotor helicopters are controlled in roll, pitch and yaw? I'm curious about fore and aft tandems like the Boeing Vertol, laterally displaced like the Fa 61, and synchropters like the Flettner Kolibri. I know all these machines use/used various combinations of differential collective and differential cyclic but I'm shady on the specifics.

Tom P.

RE: Dual Rotor Control Methods

(OP)
Thanks, Dave.  That site explains a lot.

One thing that occured to me was with all the cross coupling that can happen on laterally displaced rotors or synchropters when you use either differential cyclic or differential collective for yaw control, why has no one used rotor blade tip brakes for yaw control?  Certainly it works for co-axial designs.  Maybe not responsive enough?  Inefficient perhaps?

Tom P.

RE: Dual Rotor Control Methods

Tom,

The tip-paddles are a good method for the coaxial and they probably produce little, if any, cross couplings at slow forward speeds.  However, Kamov elected to rely solely on differential collective and they use a mechanism to switch the pedals for autorotation. Perhaps Kamov felt that their mechanism was simpler than the tip paddles, plus they were willing to put up with 'indecision's' of their mechanism at low collective settings.

Opposed cyclic is used in the tandem and, I assume, that it was also used in the side-by-side and interleaf configurations. This method should produce minimal cross couplings at slow forward speeds in the side-by-side and interleaf.  I think that it should also work properly during the transition and flight in autorotation.

Like the Kamov helicopters, yaw control of the intermeshing configuration is not perfect. Tip-paddles would eliminate the problem of switching pedals for autorotation, however they will not solve the torque-pitch coupling, because of the angle of the masts.  This is some preliminary work on yaw control for the intermeshing configuration, if interested. http://www.synchrolite.com/UniCopter_Directional.html

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