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-   -   Helicopter Dynamics: Phase Angle (https://www.pprune.org/rotorheads/19744-helicopter-dynamics-phase-angle.html)

Dave Jackson 13th August 2001 06:09

Helicopter Dynamics: Phase Angle
 
Lu; The following bits of information may answer your concern about phase lag.
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The phase lag "stems from the two components ...... one aerodynamic due to the distribution of airloads from the angular motion, the other from the gyroscopic flapping motion." ~ Padfield, [my bold]

Prouty, (I think it was him) has stated that when the control plane (swashplate) is changed by cyclic input the tip-path-plane will realign itself with the control-plane within 1/2 of a rotor's revolution.

"For blades freely articulated at the center of rotation, or teetering rotors, the response is lagged by exactly 90-degrees in hover; for hingeless rotors, such as the Lynx and Bo105, the phase angle is about 75 to 80-degrees."

It has been stated that the conventional swashplate is an ideal control mechanism for rotors with a 90-phase angle, but it is not ideal for rotors with a phase angle less than 90.
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To me it appears that Lynx's 75 to 80-degree phase angle is a compromise between the gyroscopic precession's 90-degrees and the aerodynamics' < 75-degrees.


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