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Old 22nd February 2007 | 19:07
  #25 (permalink)  
Graviman
 
Joined: Nov 2004
Posts: 1,334
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From: Cambridgeshire, UK
Kengineer-130,

I don't claim to be an expert, and certainly disregard my comments if an instructor chips in...

A helicopter cyclic movement initially controls the pitch/roll acceleration of the helicopter. The rotor responds quickly and the heli starts to swing, but it takes a while for the rate to build up. As the fuselage rolls or pitches the machine then becomes velocity control like a fixed wing. This is caused by the lag in rotor following heli, leading to an equilibrium at a fixed pitch or roll rate - basically the swash plate angle is now generating gyroscopic nutating forces. Once the heli starts to translate (or change its translational speed) flapback then leads to positional control on the cyclic.

Eventually the system will reach the attitude demanded, but the delay in response can lead to overcontroling hence reduced-g mast bumping (or PIO in hover). There is also the fact that the range of cyclic movement required for flapback (heli version of dihedral) increases stick sensitivity.

Actually a suprisingly good way to train your reflexes for the fine movements required is to thermal a glider. Being near stalling, while in a turn seems to make you much more aware of the aircraft feedback. It's been a little while since i flew anything though...

Mart

Last edited by Graviman; 24th March 2007 at 15:07. Reason: Just checked this up in Prouty...
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