Propulsion Systems for Rotorcraft

1 . A propulsion system for a rotorcraft comprising:

a first fan assembly including a plurality of first fan blades;

a second fan assembly including a plurality of second fan blades; and

a drive system adapted to provide torque to the first and second fan blades;

wherein, the first fan blades have a larger rotational inertia than the second fan blades; and

wherein, the second fan blades are adapted to experience a larger angular acceleration than the first fan blades in response to torque from the drive system, thereby providing responsive thrust control for the rotorcraft.

2 . The propulsion system as recited in claim 1 wherein the first and second fan blades further comprise fixed pitch fan blades.

3 . The propulsion system as recited in claim 1 wherein the first fan blades are longer than the second fan blades.

4 . The propulsion system as recited in claim 1 wherein the first fan blades are formed from a different material than the second fan blades.

5 . The propulsion system as recited in claim 1 wherein the plurality of first fan blades include a larger number of fan blades than the plurality of second fan blades.

6 . The propulsion system as recited in claim 1 wherein the first fan blades are wider than the second fan blades.

7 . The propulsion system as recited in claim 1 wherein the first fan blades further comprise a circumferential tip ring.

8 . The propulsion system as recited in claim 1 wherein at least one of the first or second fan assemblies further comprise a shrouded fan assembly.

9 . The propulsion system as recited in claim 1 wherein at least one of the first or second fan assemblies further comprise an open fan assembly.

10 . The propulsion system as recited in claim 1 wherein the first fan blades are adapted to provide a larger maximum thrust than the second fan blades.

11 . The propulsion system as recited in claim 1 wherein the drive system further comprises an electric motor.

12 . The propulsion system as recited in claim 1 wherein the drive system further comprises a hydraulic motor.

13 . The propulsion system as recited in claim 1 wherein the drive system further comprises a variable speed motor.

14 . A rotorcraft comprising:

a fuselage; and

a propulsion system coupled to the fuselage, the propulsion system comprising:

a first fan assembly including a plurality of first fan blades;

a second fan assembly including a plurality of second fan blades; and

a drive system adapted to provide torque to the first and second fan blades;

wherein, the first fan blades have a larger rotational inertia than the second fan blades; and

wherein, the second fan blades are adapted to experience a larger angular acceleration than the first fan blades in response to torque from the drive system, thereby providing responsive thrust control for the rotorcraft.

15 . The rotorcraft as recited in claim 14 wherein the second fan assembly further comprises a plurality of second fan assemblies.

16 . The rotorcraft as recited in claim 15 wherein the plurality of second fan assemblies further comprise at least four second fan assemblies.

17 . The rotorcraft as recited in claim 15 wherein the first fan assembly further comprises a central fan assembly including a mast; and

wherein the second fan assemblies are radially symmetric about the mast of the central fan assembly.

18 . The rotorcraft as recited in claim 17 wherein the central fan assembly forms a rotor disk and the second fan assemblies are disposed outboard of the rotor disk of the central fan assembly.

19 . The rotorcraft as recited in claim 17 wherein the central fan assembly forms a rotor disk and the second fan assemblies are disposed underneath the rotor disk of the central fan assembly.

20 . The rotorcraft as recited in claim 17 wherein the first fan blades of the central fan assembly further comprise variable pitch fan blades; and

wherein the second fan blades of the second fan assemblies further comprise fixed pitch fan blades.