Expert: Paul Soderman - 3/10/2009

Question
I would like an explanation of how a Helicopter achieves Directional Control. Similarly, how does it compensate for the increased air flow against the advancing blades, vs. the retarding blades while underway.
My thought is that the Rotor Blades constantly change pitch on every revolution which seems like a mechanical nightmare. That is to say, that to go forward, more pitch is applied as the blade is around the aft. and less pitch when the blade is around the forward of the Craft on each and every rotation. Is this True?
Thanks,   Don

Answer
Yes Don - variable rotor pitch or cyclic is exactly how helicopters operate.  Blade pitch varies during each revolution to keep loading constant and can be changed to move the helicopter in any desired direction.  That is - on the advancing side angle of attack is decreased and on the retreating side angle of attack is increased. To tilt forward and increase helicopter forward speed, the aft rotor pitch angles are increased. Thus, the total rotor thrust vector tilts forward.  Or it can be tilted left, right or backward.  A collective control changes pitch the same amount at every azimuth location so the helicopter ascends or descends.  The mechanical system is somewhat complicated, but the helicopter people have been doing it for so long that they have it pretty well optimized.  It is reliable.
Paul