In demonstrating stuck left pedal from a takeoff with my instructor yesterday when starting a nose left turn he had me stir or move the cyclic clockwise in small steady circles and pump the collective. It did slow the spin down significantly but I just don't understand why.

Any thoughts or comments would be greatly appreciated.

  • $\begingroup$ Which helicopter? Was there forward speed or were you in a hover? $\endgroup$ – Koyovis Jun 27 '17 at 19:00
  • $\begingroup$ The r22 and it was in a hover $\endgroup$ – Wes Jun 27 '17 at 20:27

The R22 has an anti-clockwise rotor. The more torque the rotor exerts, the higher the clockwise torque on the helicopter will be: nose right. With a stuck left pedal the nose wants to turn left, so we want the rotor to exert more torque.

On pumping the collective: there is an effect of how fast the collective pitch is raised, on the torque exerted. The figure below shows $C_T$ (a dimensionless measure of rotor torque) against time for a full sweep of the collective from full down to full up. Rapid deflection causes a torque overshoot, so a higher torque than a slow deflection.

enter image description here

So if the collective is raised fast and lowered more slowly, a net torque increase is generated while lowering the helicopter. Picture source: Helicopter Performance, Stability and Control by Raymond Prouty

On rotating the cyclic: cyclic pitch deflection causes angle-of-attack variation of the rotor blades, with an associated variation in blade drag, and therefore rotor torque. There is a section on this effect in the book Principles of Rotor Aerodynamics by J. Gordon Leishman (section 8.15.7 Unsteady Axial Force and Airfoil Drag). What I can distill from this chapter is that stirring the collective clockwise creates more airfoil drag, while keeping the net movements fwd/aft and left/right neutral. Unfortunately the section does not contain any helpful diagrams.

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  • $\begingroup$ Thank you so much for the explanation! I have some studying to do on it in order for it to completely sink in but I can't say thank you enough Koyovis! $\endgroup$ – Wes Jun 29 '17 at 18:36
  • $\begingroup$ No worries Wes, wishing you lots of joy riding helicopters. $\endgroup$ – Koyovis Jun 29 '17 at 23:16

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