Equations were developed for the torsional motion of a gas-turbine engine geared to a helicopter rotor in which the rotor blades were hinged to the rotor shaft. The rotor system was simplified to yield simple third-order equations that can be used in the analysis of engine control. Comparison of the system response calculated from these equations with the experimentally observed frequency response of a rotor from a 2500-pound helicopter showed satisfactory agreement.nCalculations showed that the torsional motion arising from the hinged construction of the blades contributed to the instability of the engine-speed and engine-torque controls. Trends in stability and response of controls with increasing weight of helicopters were investigated.
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