Evening all, Sorry if this intellectual chess is boring some of you. Perhaps Heliport would put this all in a new thread which you could avoid.
Krylian, you said,
Quote: I think you are over generalizing Bailey's statement. Think of what happens when you're in a hover and push forward cyclic to commence forward flight. Sure, your forward cyclic will cause the plane of rotation to tilt forward, but how? If the angle of attack doesn't change then the lift in that quadrant is unchanged and the disk won't respond.
I don't have access to books at present so someone will correct me if I'm wrong.
Don't forget flapping to equality.
i.e. If cyclic pitch is applied the blade will flap to maintain the angle of attack.
If cyclic pitch is increased the blade will flap up, reducing pitch. It is the flapping that alters the plane of rotation. There is a lag due to the inertia of the blade in the vertical plane but this is small. so in practical terms the angle of attack does not change much unless you make rapid cyclic movements. All flapping in one direction occurs within 1/2 revolution. I seem to remember reading in an NTSB document that stall develops over several revolutions.
I had a discussion with another pilot today and this came up.
Why is aft cyclic good at high RRPM but bad at low?
The answer is this. At high Nr aft cyclic increases the angle of attack, moving the autorotative region outward along the blade and increasing its efficiency. This decreases the area and drag of the end, driven section. Lovely, RRPM goes up just like we were told it would. The inboard stalled section of the blade is small and irrelevant.
As Nr falls, more of the inner section of the blade stalls, so drag here becomes relevant, but no matter, aft cyclic increases the AOA, the autorotative bit is still up to the job. As it moves out along the blade it still reduces the drag of the end bit of the blade and overpowers the extra drag of the stalled section. RRPM goes up. Still OK
Nr falls more The stalled section at the root is now big and its drag is in equilibrium with the autorotative force. The drag at the end of the blade is small in comparison. Recovery may be possible if you dont muck it up. Any increase in angle of attack will push the stalled region outward so that the drag overpowers the autorotative force. RRPM goes down and the rotor stalls. Aft cyclic doesnt look so good here. I am guessing we are in the low 70s% area, but don't really know.
Aft cyclic is great at high RRPM but you can have too much of a good thing at low RRPM.
If you dont want to call it forward cyclic you could always call it less aft cyclic.
I believe that there must be some warning of impending stall, probably left roll and pitch down. At this point you are not far off doomed as stated in R22 SN24 (which I read today, comparison to fixed wing not so ridiculous eh, snoop?). I suggest you all read SN24 before making your mind up what action if any is worth taking at this point in your life.
I do not suggest you do anything other than you were trained to do.
Last edited by Gaseous; 10th January 2005 at 21:25.