Tip gap control systems with inner duct control surfaces

1. A tip gap control system for a ducted aircraft having a vertical takeoff and landing flight mode and a forward flight mode, the tip gap control system comprising:

a flight control computer including an inner duct surface control module configured to generate an inner duct surface actuator command in response to the ducted aircraft converting between the vertical takeoff and landing flight mode and the forward flight mode; and

a proprotor system in data communication with the flight control computer, the proprotor system comprising:

a duct including a plurality of active inner duct surfaces movable into a plurality of positions including a retracted position and an extended position;

a plurality of proprotor blades surrounded by the duct; and

one or more actuators coupled to the active inner duct surfaces;

wherein, the one or more actuators are configured to move the active inner duct surfaces between the plurality of positions based on the inner duct surface actuator command, thereby controlling a tip gap between the proprotor blades and the duct;

wherein, the one or more actuators move the active inner duct surfaces to form a vertical takeoff and landing flight mode tip gap between the proprotor blades and the duct in response to the ducted aircraft converting to the vertical takeoff and landing flight mode; and

wherein, the one or more actuators move the active inner duct surfaces to form a forward flight mode tip gap between the proprotor blades and the duct in response to the ducted aircraft converting to the forward flight mode, the forward flight mode tip gap different from the vertical takeoff and landing flight mode tip gap.

2. The tip gap control system as recited in claim 1 wherein the inner duct surface actuator command further comprises a tip gap adjustment distance, the one or more actuators configured to move the active inner duct surfaces by the tip gap adjustment distance.

3. The tip gap control system as recited in claim 1 wherein the inner duct surface actuator command further comprises one of a retract command or an extend command, the one or more actuators configured to move the active inner duct surfaces by a predetermined distance in response to receiving the inner duct surface actuator command.

4. The tip gap control system as recited in claim 1 wherein the proprotor blades pass adjacent to a blade pass band on an inner surface of the duct, the active inner duct surfaces disposed along the blade pass band.

5. The tip gap control system as recited in claim 1 wherein the active inner duct surfaces are circumferentially disposed on an inner surface of the duct.

6. The tip gap control system as recited in claim 1 wherein an inner surface of the duct forms a circumferential slot, the active inner duct surfaces retractable into the circumferential slot.

7. The tip gap control system as recited in claim 1 wherein an inner surface of the duct forms a cavity; and

wherein, the active inner duct surfaces are slidably coupled to the duct at the cavity, the active inner duct surfaces slidable into the cavity in the retracted position, thereby increasing the tip gap in the retracted position.

8. The tip gap control system as recited in claim 1 wherein an inner surface of the duct forms a cavity; and

wherein, the active inner duct surfaces are hingeably coupled to the duct at the cavity, the active inner duct surfaces rotatable into the cavity in the retracted position, thereby increasing the tip gap in the retracted position.

9. The tip gap control system as recited in claim 1 wherein an inner surface of the duct forms a cavity; and

wherein, the active inner duct surfaces further comprise fluid-filled active inner duct surfaces disposed in the cavity, the fluid-filled active inner duct surfaces deflated in the retracted position and inflated in the extended position, thereby increasing the tip gap in the retracted position.

10. The tip gap control system as recited in claim 1 wherein the active inner duct surfaces are independently actuated to permit nonuniform positioning of the active inner duct surfaces.

11. A rotorcraft having a vertical takeoff and landing flight mode and a forward flight mode, the rotorcraft comprising:

a fuselage;

a flight control computer including an inner duct surface control module configured to generate an inner duct surface actuator command in response to the rotorcraft converting between the vertical takeoff and landing flight mode and the forward flight mode; and

a proprotor system coupled to the fuselage and in data communication with the flight control computer, the proprotor system comprising:

a duct including a plurality of active inner duct surfaces movable into a plurality of positions including a retracted position and an extended position;

a plurality of proprotor blades surrounded by the duct; and

one or more actuators coupled to the active inner duct surfaces;

wherein, the one or more actuators are configured to move the active inner duct surfaces between the plurality of positions based on the inner duct surface actuator command, thereby controlling a tip gap between the proprotor blades and the duct;

wherein, the one or more actuators move the active inner duct surfaces to form a vertical takeoff and landing flight mode tip gap between the proprotor blades and the duct in response to the rotorcraft converting to the vertical takeoff and landing flight mode; and

wherein, the one or more actuators move the active inner duct surfaces to form a forward flight mode tip gap between the proprotor blades and the duct in response to the rotorcraft converting to the forward flight mode, the forward flight mode tip gap different from the vertical takeoff and landing flight mode tip gap.

12. The rotorcraft as recited in claim 11 further comprising a maneuver detection module configured to detect a flight condition of the rotorcraft, the inner duct surface control module configured to determine the inner duct surface actuator command based on the flight condition;

wherein, the flight condition further comprises at least one of a flight maneuver or a flight mode.

13. A method for controlling a tip gap for a ducted aircraft having a vertical takeoff and landing flight mode and a forward flight mode, the method comprising:

generating an inner duct surface actuator command in response to the ducted aircraft converting between the vertical takeoff and landing flight mode and the forward flight mode;

transmitting the inner duct surface actuator command to a proprotor system including a duct and a plurality of proprotor blades, the duct including a plurality of active inner duct surfaces;

moving at least one of the active inner duct surfaces between a retracted position and an extended position in response to the inner duct surface actuator command, thereby controlling the tip gap between the proprotor blades and the duct;

moving at least one of the active inner duct surfaces to form a vertical takeoff and landing flight mode tip gap between the proprotor blades and the duct in response to the ducted aircraft converting to the vertical takeoff and landing flight mode; and

moving at least one of the active inner duct surfaces to form a forward flight mode tip gap between the proprotor blades and the duct in response to the ducted aircraft converting to the forward flight mode, the forward flight mode tip gap different from the vertical takeoff and landing flight mode tip gap.

14. The method as recited in claim 13 further comprising generating the inner duct surface actuator command in response to receiving a tip gap adjustment distance.

15. The method as recited in claim 14 further comprising generating the inner duct surface actuator command in response to the tip gap adjustment distance exceeding a tip gap adjustment distance threshold.

16. The method as recited in claim 13 further comprising generating the inner duct surface actuator command based on a pitch of the proprotor blades.

17. The method as recited in claim 13 further comprising retracting the active inner duct surfaces in response to detecting a structural deformity of the proprotor system.

18. The method as recited in claim 13 further comprising retracting the active inner duct surfaces in response to detecting a collision with the proprotor system.

19. The tip gap control system as recited in claim 6 wherein the one or more actuators are disposed in the circumferential slot.

20. The tip gap control system as recited in claim 1 wherein the flight control computer comprises a tip gap monitoring system including one or more strain gauges, the tip gap monitoring system configured to monitor the tip gap between the proprotor blades and the duct.