ENGAGEMENT AND DISENGAGEMENT OF TAIL ROTOR
An exemplary rotorcraft includes a propulsion system including a prime mover and a drive shaft coupled to the prime mover, the drive shaft including a coupling separating the drive shaft into an input shaft and an output shaft, the coupling operable between an engaged position rotationally coupling the input shaft and the output shaft and a disengaged position rotationally disengaging the output shaft from the input shaft, a main rotor coupled to the prime mover, a secondary rotor attached to the output shaft, and a motor coupled to the output shaft.
1 . A rotorcraft, comprising:
a propulsion system including a prime mover and a drive shaft coupled to the prime mover, the drive shaft including a coupling separating the drive shaft into an input shaft and an output shaft, the coupling operable between an engaged position rotationally coupling the input shaft and the output shaft and a disengaged position rotationally disengaging the output shaft from the input shaft;
a main rotor coupled to the prime mover;
a secondary rotor attached to the output shaft; and
a motor coupled to the output shaft.
2 . The rotorcraft of claim 1 , wherein the prime mover is an engine.
3 . The rotorcraft of claim 1 , wherein the motor is a hydraulic motor.
4 . The rotorcraft of claim 1 , wherein the motor is an electric motor.
5 . The rotorcraft of claim 1 , wherein the coupling is not a clutch.
6 . The rotorcraft of claim 1 , wherein the coupling is a sliding coupling.
7 . The rotorcraft of claim 1 , wherein the motor is coupled to the output shaft by a belt.
8 . The rotorcraft of claim 1 , wherein the prime mover is an engine;
the motor is an electric motor; and
the electric motor is coupled to a generator driven by the engine.
9 . The rotorcraft of claim 8 , wherein the electric motor is coupled to the output shaft by a belt.
10 . The rotorcraft of claim 1 , wherein the prime mover is an engine;
the motor is an electric motor; and
the electric motor is coupled to a battery.
11 . A method, comprising:
operating a rotorcraft comprising a propulsion system including a prime mover and a drive shaft coupled to the prime mover, the drive shaft including a coupling separating the drive shaft into an input shaft and an output shaft, a main rotor coupled to the prime mover, and a secondary rotor coupled to the output shaft, the coupling operable between an engaged position rotationally coupling the input shaft and the output shaft and a disengaged position rotationally disengaging the output shaft from the input shaft;
actuating the coupling to the disengaged position disengaging the secondary rotor from the prime mover; and
spooling up the main rotor with the prime mover while the secondary rotor is disengaged from the prime mover.
12 . The method of claim 11 , wherein the coupling is not a clutch.
13 . The method of claim 11 , wherein the coupling is a sliding spline coupling.
14 . The method of claim 11 , further comprising driving, when the coupling in the disengaged position, the output shaft with a motor to a speed synchronous with the input shaft driven by the prime mover; and
actuating the coupling to the engaged position when the input shaft speed and the output shaft speed are synchronous.
15 . The method of claim 14 , wherein the prime mover is an engine and the motor is an electric motor.
16 . The method of claim 14 , further comprising driving the main rotor and the secondary rotor with the prime mover at a flight speed.
17 . The method of claim 16 , further comprising disengaging the motor from the output shaft via a clutch when the prime mover is driving the main rotor and the secondary rotor at the flight speed.
18 . The method of claim 11 , further comprising driving the main rotor and the secondary rotor with the prime mover while the coupling is in the engaged position;
actuating the coupling to the disengaged position while the prime mover is driving the main rotor and the input shaft; and
braking rotation of the secondary rotor with an electric motor coupled to the output shaft.
19 . The method of claim 18 , further comprising an electric power source connected to the electric motor; and
charging the electric power source with the electric motor while braking the secondary rotor.
20 . The method of claim 11 , further comprising driving, when the coupling in the disengaged position, the output shaft with a motor to a speed synchronous with the input shaft driven by the prime mover;
actuating the coupling to the engaged position when the input shaft speed and the output shaft speed are synchronous;
driving the main rotor and the secondary rotor with the prime mover while the coupling is in the engaged position; and
actuating the coupling to the disengaged position while the prime mover is driving the main rotor and the input shaft.