PPRuNe Forums - View Single Post - Helicopter Dynamics: Gyroscopic Precession
Old 13th Mar 2014, 22:04
  #109 (permalink)  
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Maximum pitch, associated with maximum (but constant) lift, occurs 90 degrees away from maximum rate of change of pitch (and lift).
Where pitch changes most quickly is not where the lift is a maximum or minimum, it's where it has the average value.
negative ghostrider - don't confuse pitch angle with angle of attack - it is AoA that determines lift and that is max/min at the point of maximum rate of pitch change. The max/min AoA gives the max rate of blade flapping. The reason that the AoA decreases/increases towards the high/low point is aerodynamic damping - a blade flapping up (due to high AoA) meets air coming from above which gradually reduces the AoA and thus the lift.

When the blade gets to its high/low point the pitch change starts in the opposite direction.

Maybe it does, but where is it?

There's a cyclic control input to move to the left.
Is the maximum-minimum-lift/lowest-highest-blade-tip direction fore-and-aft or left-to-right?
With no advance angle on either the jacks or the pitch change horn, the swash plate would have to be tilted to the right to enable the disc to tilt forwards (in your example the left cyclic would result in an aft tilt of the disc with the maximum rate of pitch change/AoA/flap down in the 9 o'clock position) On most helicopters the jacks/pitch change rods are organised so that the disc follows the swash plate tilt because the pitch changes are made 90 degrees ahead of the desired disc attitude.
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