Rotorcraft having propeller generated power during autorotations

1. A rotorcraft having an engine powered mode and an autorotation mode, the rotorcraft comprising:

a fuselage;

a tailboom coupled to and extending aftwardly from the fuselage;

a flight stabilizer including first and second horizontal stabilizers coupled to and extending laterally from the tailboom such that the horizontal stabilizers are aft of the fuselage;

an engine disposed within the fuselage;

a drivetrain configured to receive torque and rotational energy from the engine in the engine powered mode;

a main rotor system coupled to the drivetrain and rotatable to generate lift and forward thrust for the rotorcraft in the engine powered mode;

a pusher propeller coupled to the drivetrain and rotatable to generate forward thrust for the rotorcraft in the engine powered mode, the pusher propeller coupled to the tailboom and positioned aft of the horizontal stabilizers; and

a tail rotor system coupled to the drivetrain and rotatable to generate anti-torque thrust for the rotorcraft in the engine powered mode, the tail rotor system coupled to the tailboom and positioned aft of the pusher propeller such that the pusher propeller is interposed between the horizontal stabilizers and the tail rotor system;

wherein, in the autorotation mode, the pusher propeller is aerodynamically driven responsive to airflow therethrough and the drivetrain is configured to receive torque and rotational energy from the pusher propeller, thereby providing power to the main rotor system.

2. The rotorcraft as recited in claim 1 wherein the drivetrain further comprises a transmission between the engine and the main rotor system, the transmission configured to adjust a rotating speed ratio between the engine and the main rotor system.

3. The rotorcraft as recited in claim 2 wherein the drivetrain further comprises a driveshaft coupling the transmission and the pusher propeller.

4. The rotorcraft as recited in claim 2 wherein the drivetrain further comprises a freewheeling unit coupled between the engine and the transmission.

5. The rotorcraft as recited in claim 4 wherein the freewheeling unit further comprises a sprag clutch.

6. The rotorcraft as recited in claim 1 wherein the main rotor system further comprises a non-rigid main rotor system.

7. The rotorcraft as recited in claim 1 wherein the main rotor system further comprises a fully articulated main rotor system.

8. The rotorcraft as recited in claim 1 wherein the main rotor system further comprises a plurality of rotor blades coupled to a rotor hub such that each rotor blade is configured to independently flap relative to the rotor hub about a flapping axis.

9. The rotorcraft as recited in claim 1 wherein the pusher propeller further comprises a plurality of variable pitch rotor blades.

10. The rotorcraft as recited in claim 9 wherein the pitch of the rotor blades of the pusher propeller is collectively controllable.

11. The rotorcraft as recited in claim 9 wherein the pitch of the rotor blades of the pusher propeller is greater in the engine powered mode than in the autorotation mode of the rotorcraft.

12. The rotorcraft as recited in claim 9 further comprising a manual input for reducing the pitch of the rotor blades of the pusher propeller when the rotorcraft transitions from the engine powered mode to the autorotation mode.

13. The rotorcraft as recited in claim 9 further comprising a flight control system configured to reduce the pitch of the rotor blades of the pusher propeller when the rotorcraft transitions from the engine powered mode to the autorotation mode.

14. The rotorcraft as recited in claim 1 wherein the tail rotor system further comprises variable pitch rotor blades.

15. The rotorcraft as recited in claim 1 wherein the flight stabilizer further comprises first and second vertical fins coupled to respective outboard ends of the first and second horizontal stabilizers.

16. The rotorcraft as recited in claim 1 wherein the flight stabilizer further comprises a central vertical fin on an underside of the tailboom to provide yaw stability and to protect the pusher propeller from ground strikes.

17. A rotorcraft having an engine powered mode and an autorotation mode, the rotorcraft comprising:

a fuselage;

a tailboom coupled to and extending aftwardly from the fuselage;

a flight stabilizer including first and second horizontal stabilizers coupled to and extending laterally from the tailboom such that the horizontal stabilizers are aft of the fuselage;

an engine disposed within the fuselage;

a drivetrain configured to receive torque and rotational energy from the engine in the engine powered mode;

a main rotor system coupled to the drivetrain and rotatable to generate lift and forward thrust for the rotorcraft in the engine powered mode;

a pusher propeller coupled to the drivetrain and rotatable to generate forward thrust for the rotorcraft in the engine powered mode, the pusher propeller including a plurality of variable pitch rotor blades, the pusher propeller coupled to the tailboom and positioned aft of the horizontal stabilizers;

a tail rotor system coupled to the drivetrain and rotatable to generate anti-torque thrust for the rotorcraft in the engine powered mode, the tail rotor system coupled to the tailboom and positioned aft of the pusher propeller such that the pusher propeller is interposed between the horizontal stabilizers and the tail rotor system; and

a flight control system configured to collectively control the pitch of the rotor blades of the pusher propeller;

wherein, in response to the rotorcraft transitioning from the engine powered mode to the autorotation mode, the flight control system reduces the pitch of the rotor blades of the pusher propeller; and

wherein, in the autorotation mode, the pusher propeller is aerodynamically driven responsive to airflow therethrough and the drivetrain is configured to receive torque and rotational energy from the pusher propeller, thereby providing power to the main rotor system.

18. The rotorcraft as recited in claim 17 wherein the drivetrain further comprises:

a transmission between the engine and the main rotor system, the transmission configured to adjust a rotating speed ratio between the engine and the main rotor system;

a driveshaft coupling the transmission and the pusher propeller; and

a freewheeling unit coupled between the engine and the transmission.

19. The rotorcraft as recited in claim 17 wherein the main rotor system further comprises a fully articulated main rotor system including a plurality of rotor blades coupled to a rotor hub such that each rotor blade is configured to independently flap relative to the rotor hub about a flapping axis.

20. A rotorcraft having an engine powered mode and an autorotation mode, the rotorcraft comprising:

a fuselage;

a tailboom coupled to and extending aftwardly from the fuselage;

a flight stabilizer including first and second horizontal stabilizers coupled to and extending laterally from the tailboom such that the horizontal stabilizers are aft of the fuselage;

an engine disposed within the fuselage;

a drivetrain configured to receive torque and rotational energy from the engine in the engine powered mode;

a main rotor system coupled to the drivetrain and rotatable to generate lift and forward thrust for the rotorcraft in the engine powered mode, the main rotor system including a plurality of rotor blades coupled to a rotor hub such that each rotor blade has a pitching degree of freedom and a flapping degree of freedom;

a pusher propeller coupled to the drivetrain and rotatable to generate forward thrust for the rotorcraft in the engine powered mode, the pusher propeller coupled to the tailboom and positioned aft of the horizontal stabilizers; and

a tail rotor system coupled to the drivetrain and rotatable to generate anti-torque thrust for the rotorcraft in the engine powered mode, the tail rotor system coupled to the tailboom and positioned aft of the pusher propeller such that the pusher propeller is interposed between the horizontal stabilizers and the tail rotor system;

wherein, in the autorotation mode, the pusher propeller is aerodynamically driven responsive to airflow therethrough and the drivetrain is configured to transfer torque and rotational energy from the pusher propeller to the main rotor system to counteract main rotor speed decay and aid in main rotor speed recovery; and

wherein, in the autorotation mode, a glide speed of the rotorcraft is controlled responsive to cyclic pitch control and rotor blade flapping of the main rotor system such that the pusher propeller acts solely as a wind turbine.