PPRuNe Forums - View Single Post - Positive aircraft control vs. stabilized or stable flight
Old 27th Apr 2020, 13:41
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JimEli
 
Join Date: Dec 2006
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Originally Posted by cpt
Hello Blazkowic,

"positive aircraft control" rings me a bell about a system that was installed on S76s when equipped with the phase2 and3 autopilots. It was called the Pitch Bias Actuator (PBA) and it was designed to: "improve the longitudinal stability of the helicopter and give the cyclic a positive control position gradient in pitch"
In short, when you were accelerating, it was supposed to increase the need of forward motion with the cyclic, and also to compensate the natural tendancy of the rotor to tilt fore and back with the variations of power (collective pitch)
In case of system malfunction we could deactivate this system by pulling its circuit breaker.
Personally, I've never noticed much difference with or without this system operating.
A PBA was installed on the A model UH-60 also. Strangely, it was conspicuously required to be deactivated and removed from the aircraft during the period the helicopter was grounded for pitch-over accidents. Oddly, the stabilator which was conclusively determined NOT to cause any of the pitch-over accidents, received all the attention and took the blame.

Sorry for the hijack.

Last edited by JimEli; 27th Apr 2020 at 13:54.
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