Gust alleviating control for a coaxial rotary wing aircraft

1. A flight control system for a coaxial rotary wing aircraft comprising a main rotor system and an active elevator, the flight control system comprising:

a flight control computer that interfaces with the main rotor system and the active elevator, the flight control computer comprising processing circuitry configured to execute control logic comprising:

a gust detector that produces a gust error indicative of a wind gust encountered by the coaxial rotary wing aircraft; and

a gust alleviation control that reduces lift on the main rotor system with collective, based on the gust error, and mixes a collective command to a main rotor cyclic and a differential cyclic to reduce an aircraft pitch response and a lift-offset change, and further wherein the gust alleviation control reduces a main rotor pitching moment with the main rotor cyclic, based on the gust error, and mixes a main rotor cyclic command to the active elevator to reduce the aircraft pitch response.

2. The flight control system according to claim 1 , wherein the gust detector comprises a pitch rate model that maps a pitch rate command into either an expected load factor or an expected angle-of-attack.

3. The flight control system according to claim 2 , wherein the gust detector compares either the expected load factor or the expected angle-of-attack to a sensed load factor or an observed angle-of-attack to determine an aircraft disturbance.

4. The flight control system according to claim 3 , wherein the gust detector applies a dead-band to the aircraft disturbance and produces the gust error.

5. The flight control system according to claim 1 , wherein the gust alleviation control further comprises collective-based dynamic shaping of the gust error to quicken and scale the gust error as a collective-control quickened gust error.

6. The flight control system according to claim 5 , wherein the gust alleviation control applies a limiter to the collective-control quickened gust error as a collective-control limited quickened gust error to restrict authority of the collective control response.

7. The flight control system according to claim 6 , wherein the gust alleviation control sums the collective-control limited quickened gust error with a pilot collective command to produce an augmented pilot collective command.

8. The flight control system according to claim 7 , wherein the gust alleviation control further comprises a mixer that outputs a ganged pitch cyclic command, the collective command, and a differential lateral cyclic command to reduce the aircraft pitch response and a lift offset response to the augmented pilot collective command.

9. The flight control system according to claim 1 , wherein the gust alleviation control further comprises elevator-control dynamic shaping of the gust error to quicken and scale the gust error for elevator control as an elevator-control quickened gust error.

10. The flight control system according to claim 9 , wherein the gust alleviation control applies a limiter to the elevator-control quickened gust error as an elevator-control limited quickened gust error to restrict authority of the elevator control response.

11. The flight control system according to claim 10 , further comprising a delay element that transforms the elevator-control limited quickened gust error into an elevator command.

12. The flight control system according to claim 11 , further comprising a transformed elevator command filter that produces the main rotor cyclic command based on the elevator command in order to reduce the aircraft pitch response.

13. A method of gust alleviation on a coaxial rotary wing aircraft comprising a main rotor system and an active elevator, the method comprising:

producing, by a gust detector, a gust error indicative of a wind gust encountered by the coaxial rotary wing aircraft;

reducing lift on the main rotor system with collective, by a gust alleviation control, based on the gust error;

mixing a collective command to a main rotor cyclic and a differential cyclic to reduce an aircraft pitch response and a lift-offset change;

reducing a main rotor pitching moment with the main rotor cyclic based on the gust error; and

mixing a main rotor cyclic command to the active elevator to reduce the aircraft pitch response.

14. The method according to claim 13 , further comprising:

performing collective-based dynamic shaping of the gust error to quicken and scale the gust error as a collective-control quickened gust error;

limiting the collective-control quickened gust error as a collective-control limited quickened gust error to restrict authority of the collective control response;

summing the collective-control limited quickened gust error with a pilot collective command to produce an augmented pilot collective command; and

outputting a ganged pitch cyclic command, the collective command, and a differential lateral cyclic command to reduce the aircraft pitch response and a lift offset response to the augmented pilot collective command.

15. The method according to claim 13 , further comprising:

performing elevator-control dynamic shaping of the gust error to quicken and scale the gust error for elevator control as an elevator-control quickened gust error;

limiting the elevator-control quickened gust error as an elevator-control limited quickened gust error to restrict authority of the elevator control response;

delaying the elevator-control limited quickened gust error to transform the elevator-control limited quickened gust error into an elevator command; and

applying a transformed elevator command filter to produce the main rotor cyclic command based on the elevator command in order to reduce the aircraft pitch response.