Assisted landing systems for rotorcraft

1. A propulsion assembly for a rotorcraft comprising:

a blade assembly;

a drive shaft coupled to the blade assembly;

an electric motor coupled to the drive shaft and operable to provide rotational energy to the drive shaft to rotate the blade assembly; and

a single use landing assistance turbine coupled to the drive shaft and operable to selectively provide rotational energy to the drive shaft during an underpowered descent to rotate the blade assembly and provide upward thrust, thereby reducing a descent rate of the rotorcraft prior to landing.

2. The propulsion assembly as recited in claim 1 wherein the blade assembly further comprises a fan blade assembly including a plurality of fixed pitch fan blades.

3. The propulsion assembly as recited in claim 1 wherein the blade assembly further comprises a rotor blade assembly including a plurality of variable pitch rotor blades.

4. The propulsion assembly as recited in claim 1 wherein the electric motor is interposed between the blade assembly and the landing assistance turbine, the electric motor and the landing assistance turbine forming a stacked arrangement.

5. The propulsion assembly as recited in claim 1 wherein the landing assistance turbine is adapted to provide the upward thrust for a duration between about 1 and about 10 seconds.

6. The propulsion assembly as recited in claim 1 wherein the drive shaft further comprises a clutch interposed between the electric motor and the landing assistance turbine.

7. The propulsion assembly as recited in claim 1 wherein the landing assistance turbine further comprises a solid fuel turbine.

8. The propulsion assembly as recited in claim 7 wherein the solid fuel turbine further comprises a solid fuel chamber adapted to contain a solid fuel and an oxidant chamber adapted to contain an oxidant.

9. The propulsion assembly as recited in claim 8 wherein the solid fuel and the oxidant are replaceable after use.

10. The propulsion assembly as recited in claim 8 wherein the solid fuel turbine further comprises a controllable speed turbine including a throttle, the throttle operable to selectively release oxidant for combustion with the solid fuel, thereby selectively controlling the upward thrust.

11. The propulsion assembly as recited in claim 10 wherein the throttle is operable to vary the release of oxidant in response to input from a flight control computer.

12. The propulsion assembly as recited in claim 10 wherein the throttle is operable to vary the release of oxidant in response to input from a pilot of the rotorcraft.

13. The propulsion assembly as recited in claim 1 wherein the underpowered descent of the rotorcraft is caused by at least partial failure of the electric motor.

14. The propulsion assembly as recited in claim 1 wherein the landing assistance turbine further comprises a combustion chamber to contain a combustion reaction, the combustion reaction producing exhaust and wherein the landing assistance turbine further comprises an exhaust subsystem to release the exhaust.

15. The propulsion assembly as recited in claim 1 further comprising a nacelle at least partially containing the drive shaft, the electric motor and the landing assistance turbine.

16. A rotorcraft comprising:

a fuselage; and

a plurality of propulsion assemblies coupled to the fuselage, each propulsion assembly further including:

a blade assembly;

a drive shaft coupled to the blade assembly;

an electric motor coupled to the drive shaft and operable to provide rotational energy to the drive shaft to rotate the blade assembly; and

a single use landing assistance turbine coupled to the drive shaft and operable to selectively provide rotational energy to the drive shaft during an underpowered descent to rotate the blade assembly and provide upward thrust, thereby reducing a descent rate of the rotorcraft prior to landing.

17. The rotorcraft as recited in claim 16 wherein at least one of the plurality of propulsion assemblies is subject to a malfunction caused by a failure of the electric motor;

wherein the non-malfunctioning propulsion assemblies in the plurality of propulsion assemblies provide upward thrust during the underpowered descent; and

wherein the landing assistance turbine of the malfunctioning propulsion assembly is adapted to provide upward thrust during a descent rate reduction maneuver prior to landing to safely land the rotorcraft.

18. The rotorcraft as recited in claim 16 wherein the rotorcraft further comprises a quadcopter and the plurality of propulsion assemblies further comprises four fan assemblies.

19. The rotorcraft as recited in claim 16 further comprising one or more wings supported by the fuselage, the plurality of propulsion assemblies coupled to the one or more wings.