Helicopter engine speed enhancement during heavy rotor load and rapid descent rate maneuvering

A control for a helicopter engine having a free turbine for normally driving the helicopter rotors at a rated speed, comprising:

• means for providing an actual speed signal indicative of the rotary speed of the free turbine;
• fuel valve means for metering fuel to said engine at a rate determined by a fuel command signal applied thereto;
• and
• fuel controlling signal processing means connected for response to said actual speed signal, for providing a reference speed signal indicative of desired rotary speed of the free turbine which reference speed signal normally indicates said rated speed and which reference speed signal alternatively indicates a speed greater than said rated speed in response to high rotor load and high descent rate maneuvers, for providing, in response to said actual speed signal and said reference speed signal, a speed error signal indicative of the difference in turbine speed indicated by said actual speed signal and said reference speed signal, and for providing said fuel command signal to said fuel valve means indicative of a desired fuel flow rate as a function of said speed error signal;
• characterized by:
• a vertical accelerometer for providing a vertical acceleration signal indicative of acceleration of the helicopter in a direction substantially parallel to the rotary axis of the main rotor;
• vertical descent rate means for providing a vertical descent rate signal indicative of the vertical descent rate of the helicopter;
• pitch angle means for providing a pitch angle signal indicative of the pitch angle of the helicopter;
• roll angle means for providing a roll angle signal indicative of the roll angle of the helicopter;
• and
• said fuel controlling signal processing means comprising means responsive to said vertical acceleration signal indicating positive vertical acceleration in excess of a threshold magnitude, said threshold magnitude being a function of said vertical descent rate signal, for providing successively greater speed increasing increments to said reference speed signal to reach a predetermined reference speed signal indicating a reference speed in excess of rated speed, for providing said predetermined reference speed signal for at least a predetermined time, and responsive to the lapse of said predetermined time, said vertical acceleration signal indicating a positive vertical acceleration which is less than a predetermined threshold magnitude, said pitch angle signal indicating a helicopter pitch angle which is less than a pitch angle threshold magnitude and said roll angle signal indicating a helicopter roll angle which is less than a roll angle threshold magnitude for providing successively greater decrements to said reference speed signal to reach a reference speed signal indicative of rated speed.