Upper surface louvers for lift fans

1. A fan apparatus, comprising:

a duct having an inlet opening,

a fan mounted in the duct, and

a plurality of louver devices positioned at the inlet opening, each louver device having an open position and a closed position, wherein each louver device includes a moveable louver portion rotatable relative to the inlet opening and a control horn fixed to the moveable louver portion, and

a linkage bar, each control horn being rotatable connected to the linkage bar,

wherein linear motion of the linkage bar is translated to rotation of the movable louver portions by the control horns, to transition the plurality of louver devices between the open and closed positions, and

wherein a shape of the control horn varies across the plurality of louver devices, and the angular range of rotation of each moveable louver portion varies between louver devices depending on the shape of the corresponding control horn.

2. The fan apparatus of claim 1 , wherein:

adjacent louver devices define a plurality of airflow channels, each airflow channel having a curvature profile that changes as the plurality of louver devices move between the open and closed positions,

each airflow channel has a first portion proximal to the fan, and a second portion distal from the fan, the first portion of said airflow channel remaining fixed relative to the fan as the plurality of louver devices move between the open and closed positions, and

the fan has blades rotating in a plane perpendicular to a rotational axis, the first portion of each airflow channel directing airflow in a direction perpendicular to the plane.

3. The fan apparatus of claim 1 , wherein each louver device has a distal edge portion that points toward a flow of air approaching the duct, the distal edge portion being adjustable to maintain an angle of attack between positive and negative ten degrees.

4. The fan apparatus of claim 1 , wherein each louver device has a fixed louver portion proximal to the fan that stays in a fixed position relative to the duct and the fan, and the moveable louver portion is distal from the fan.

5. The fan apparatus of claim 4 , wherein each moveable louver portion of the plurality of louver devices is hinged to the respective fixed louver portion.

6. The fan apparatus of claim 4 , wherein each louver device has a different airfoil shape.

7. The fan apparatus of claim 4 , further including an actuator member connected to the plurality of louver devices that is moveable in a longitudinal direction to drive movement of the plurality of louver devices between the open and closed positions.

8. The fan apparatus of claim 7 , wherein each fixed louver portion of the plurality of louver devices is rigidly connected to a strut structure extending in the longitudinal direction, the actuator member being contained in the strut structure.

9. The fan apparatus of claim 1 , wherein each control horn has a curved shape.

10. The fan apparatus of claim 9 , wherein each control horn includes a head portion and a tail portion connected by an arm portion, the length of the arm portion varying across the plurality of louver devices.

11. The fan apparatus of claim 10 , wherein the tail portion of each control horn is received in a slot of a fixed portion of the respective louver device.

12. The fan apparatus of claim 1 , wherein the plurality of louver devices is moved between the open position and the closed position by a single actuator.

13. The fan apparatus of claim 1 , wherein the difference between the angular ranges of rotation of the moveable louver portions is determined by the difference in shapes of the control horns.

14. The fan apparatus of claim 1 , wherein each moveable louver portion has a greater angular range of rotational movement between the open position and the closed position compared to upstream moveable louver portions.

15. The fan apparatus of claim 1 , wherein, in each louver device:

the control horn has a first end fixed to the moveable louver portion and a second end rotatably connected to the linkage bar,

the moveable louver portion and control horn are rotatable relative to the inlet opening, around a hinge,

the first end of the control horn is restrained from linear movement by the hinge,

the control horn is rotated around the hinge by linear movement of the linkage bar, and

the moveable louver portion is rotated between the open and closed positions by rotation of the control horn.

16. An aircraft, comprising:

a lift fan mounted in a duct,

an airfoil structure containing the lift fan and having an upper airfoil surface including a lift fan intake cover having a plurality of louver devices configured to move between an open position and a closed position when the aircraft transitions from a hover mode to a horizontal flight mode,

wherein:

a moveable portion of each louver device has an airfoil shape, the airfoil shape varying between louver devices along a longitudinal axis of the duct,

the longitudinal axis coincides with a relative wind direction when the aircraft is in the horizontal flight mode,

the plurality of louver devices is moved between the open position and the closed position by a single actuator,

the actuator is connected to a linkage bar, and the linkage bar is pivotably connected to each louver device,

the linkage bar is connected to a control horn of each louver device,

each control horn is fixed to the corresponding moveable louver portion,

a shape of the control horn varies across the plurality of louver devices,

the angular range of rotational movement between the open position and the closed position of each louver device depends on the shape of the respective control horn, and

each moveable louver portion has a greater angular range of rotational movement between the open position and the closed position compared to upstream moveable louver portions.

17. The aircraft of claim 16 , wherein each louver device has a fixed louver portion proximal to the lift fan that stays in a fixed position relative to the lift fan, and the moveable louver portion is distal from the lift fan.

18. The aircraft of claim 16 , wherein, each control horn has a curved shape and includes a head portion and a tail portion connected by an arm portion, the variation of shape between the control horns is a variation in a length of the arm portion, and the difference between the angular ranges of rotation of the moveable louver portions is determined by the difference in the lengths of the arm portions.

19. A method of controlling airflow into a lift fan on an aircraft during a transition phase between a hover mode and a horizontal flight mode, comprising:

using a plurality of louver devices extending over a lift fan of an airfoil surface to direct airflow, and

rotating a distal portion of each louver device between open and closed positions, including rotating each distal portion through a different angular range of rotation by translating linear motion of a linkage bar to rotational motion with a control horn of each louver device,

wherein a shape of the control horn varies between louver devices along the fore-to-aft direction of the aircraft, and the angular range and rate of rotation of each distal portion varies between louver devices depending on the shape of the corresponding control horn.