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What is helicopter rotor droop?


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March 09, 2012 12:20PM

Helicopters fly by means of an angle of attack increase in the main - rotor disc. However - when this angle of attack increases, the drag experienced on the blades also increases which tends to want to slow the blades down. To avoid that, a gas turbine helicopter engine will have what is called a Power Turbine Governor or PTG. This control unit senses increases in torque values when the pilot pulls up on collective and distributes more fuel into the engine in order to get more output to counter the increase in drag on the rotor blades, thus maintaining a constant rotor RPM in all operating conditions. Rotor 'droop' is when the rotor RPM drops below a minimum given parameter and can be caused by a variety of problems.