Method and apparatus for an engine inlet for a ram-air system with an icing bypass

1. An aircraft comprising:

a computer;

a fuselage;

an engine housed in the fuselage;

a ram-air engine inlet formed on an exterior of the fuselage, the ram-air engine inlet being defined, at least in part, by a cowling door, the cowling door being moveable between a closed position and an open position;

wherein the computer determines whether forward airspeed of the aircraft provides sufficient ram air flow to the engine through the ram-air engine inlet and opens or closes the cowling door responsive to the determination of whether the forward airspeed of the aircraft provides sufficient ram air flow to the engine;

an intake duct fluidly coupling the ram-air engine inlet to the engine;

a filter disposed across the intake duct;

a bypass duct formed in the ram-air engine inlet aft of the intake duct, the bypass duct operable to be selectively opened and closed; and

wherein the computer determines whether flight conditions are sufficient to cause ice formation and opens or closes the bypass duct responsive to the determination of whether the flight conditions are sufficient to cause ice formation.

2. The aircraft of claim 1 , wherein the aircraft is a tiltrotor aircraft.

3. The aircraft of claim 1 , wherein the bypass duct comprises a door that is moveable between a closed position and an open position.

4. The aircraft of claim 3 , wherein the door of the bypass duct is actuated by at least one of an electric actuator and a hydraulic actuator.

5. The aircraft of claim 1 , wherein, when in the open position, the bypass duct facilitates passage of ice out of the ram-air engine inlet.

6. The aircraft of claim 5 , wherein the bypass duct reduces occlusion of the filter.

7. The aircraft of claim 1 , wherein a plane of the ram-air engine inlet is substantially perpendicular to a plane of the filter.

8. The aircraft of claim 1 , wherein, in the closed position, the cowling door conceals the filter and an entrance to the intake duct.

9. The aircraft of claim 1 , wherein, in the open position, the cowling door reduces restrictions to air flow into the intake duct.

10. A ram-air system for an aircraft, the ram-air system comprising:

a computer;

a ram-air engine inlet comprising a cowling door, the cowling door being defined, at least in part, by a pair of side walls and a cross member disposed between and coupling the pair of side walls;

wherein the computer determines whether forward airspeed of the aircraft provides sufficient ram air flow through the ram-air engine inlet and opens or closes the cowling door responsive to the determination of whether the forward airspeed of the aircraft provides sufficient ram air flow;

a bypass duct formed in an aft aspect of the cowling door, the bypass duct operable to be selectively opened and closed; and

wherein the computer determines whether flight conditions are sufficient to cause ice formation and opens or closes the bypass duct responsive to the determination of whether the flight conditions are sufficient to cause ice formation.

11. The ram-air system of claim 10 , wherein the cowling door abuts a fuselage.

12. The ram-air system of claim 11 , wherein the cowling door is hingedly coupled to the fuselage along an aft edge of the cowling door.

13. The ram-air system of claim 11 , wherein the cowling door is hingedly coupled to the fuselage along at least one of the pair of side walls.

14. The ram-air system of claim 10 , wherein the bypass duct comprises a door that is moveable between a closed position and an open position.

15. The ram-air system of claim 10 , wherein the cowling door is hingedly coupled to a nacelle.

16. A method of operating a ram-air system, the method comprising:

determining if forward airspeed of an aircraft provides sufficient airflow through a ram-air engine inlet;

responsive to a determination that the forward airspeed of the aircraft does not provide sufficient ram air flow through the ram-air engine inlet, opening a cowling door;

responsive to a determination that the forward airspeed of the aircraft provides sufficient ram air flow through the ram-air engine inlet, closing the cowling door;

determining if flight conditions are sufficient to cause ice formation;

responsive to a determination that flight conditions are not sufficient to cause ice formation, closing a bypass duct; and

responsive to a determination that flight conditions are sufficient to cause ice formation, opening the bypass duct.

17. The method of claim 16 , wherein the determining if forward airspeed of an aircraft provides sufficient airflow through a ram-air engine inlet is performed by a flight-control computer.

18. The method of claim 16 , wherein:

the opening the cowling door is performed by a flight-control computer; and

the closing the cowling door is performed by the flight-control computer.

19. The method of claim 16 , wherein the determining if flight conditions are sufficient to cause ice formation is performed by a flight-control computer.

20. The method of claim 16 , wherein:

the closing the bypass duct is performed by a flight-control computer; and

the opening the bypass duct is performed by the flight-control computer.