Tilting a helicopter rotor, does it create torque?

  • Thread starter Moafak m
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Hello
I am making a helicopter flight simulation and I need an answer to this question:
when you push the cyclic forward, does this create a torque which will rotate the helicopter.
if the answer is yes, please tell me what counteracts this torque and stops the rotation when I return the cyclic stick to its original position.

if the answer is no, how can you explain that the lift force doesn't pass through the body's center of mass and yet doesn't have a torque.

(I assume lift force is represented as a vector which is always perpendicular to the rotor's plain of rotation)
 

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  • #2
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Yes you are correct that forward cyclic input causes the lift force vector to be off set from the aircraft center of mass and thereby creates a moment or torque about the lateral axis of the aircraft which in turn causes the aircraft to rotate on that axis.

The moment goes away when you neutralize the cyclic because the thrust vector is now back in line with the aircraft center of mass again. The aircraft would, by Newtons 1st law, keep rotating except there is a large aerodynamic damping force generated by the change in the relative wind at the rotor blade from the tangential blade velocity of rotation on the lateral axis.

If the pilot however wanted to stop the rotation faster he would not just neutralize the cyclic but he would over correct to create the opposite moment until the aircraft stopped rotating then he would neutralize the cyclic.
 
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I should also add that the description above is more accurate for a teetering, semi-rigid type of rotor. However, in a rotor system which has hinge offset, whether it be an actual hinge or some kind of flexible member, or even a rigid rotor hub, there is also a control moment generated just from the difference in lift between one side of the disc and the other and is independent of the angle change of the total rotor thrust vector. Plus it still generates the moment from the thrust vector angle. Therefore a rotor with hinge offset can create a larger control moment than one without and the larger the hinge offset, the larger the the control moment such a rotor can produce.

This is why a helicopter with hinge offset, as large as the jolly green giant or as small as a hughes 500, can be seen performing rolls and loops. Where a helicopter with a teetering rotor whether it be an R22 or BHT-214ST will probably never be seen performing any such maneuver.
 

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