Gas turbine engine with axial movable fan variable area nozzle

1. A turbofan engine comprising:

a fan section including a plurality of fan blades, the plurality of fan blades having a design angle of incidence;

a gear train having a gear reduction ratio of greater than 2.5:1;

a low pressure turbine driving the plurality of fan blades through the gear train, the low pressure turbine having a pressure ratio greater than 5:1;

a fan nacelle and a core nacelle, the fan nacelle at least partially surrounding the core nacelle;

a fan bypass flow path defined between the core nacelle and the fan nacelle, and a bypass ratio greater than 10:1;

a fan variable area nozzle in communication with the fan bypass flow path and defining a fan nozzle exit area between the fan nacelle and the core nacelle;

a duct defined between the fan nacelle and the core nacelle forward of the fan variable area nozzle, the duct having a duct maximum area, wherein the duct maximum area is greater than the fan nozzle exit area with the fan variable area nozzle in a fully open position;

a controller in communication with the fan variable area nozzle;

wherein the controller is configured to cause the fan variable area nozzle to vary the fan nozzle exit area to adjust fan bypass air flow in the fan bypass flow path in a plurality of flight conditions and maintain an angle of incidence of the plurality of fan blades in the plurality of flight conditions that is close to the design angle of incidence on the plurality of fan blades;

wherein the controller is configured to cause the fan variable nozzle to decreases the fan nozzle exit area for a cruise operating condition; and

wherein the controller is configured to cause the fan variable nozzle to increases the fan nozzle exit area for a landing operating condition.

2. The turbofan engine as recited in claim 1 , wherein the fan variable area nozzle includes a plurality of sectors, and each of the plurality of sectors are simultaneously moveable.

3. The turbofan engine as recited in claim 2 , further comprising a two stage high pressure turbine, and wherein the gear train includes a planetary gear system.

4. The turbofan engine as recited in claim 3 , further comprising a low spool including a low pressure compressor and the low pressure turbine, the low spool driving the low pressure compressor and the planetary gear system.

5. The turbofan engine as recited in claim 4 , wherein the low pressure turbine is a three stage low pressure turbine.

6. The turbofan engine as recited in claim 1 , wherein the plurality of fan blades include a fixed stagger angle.

7. The turbofan engine as recited in claim 6 , wherein the controller is configured to control the fan variable area nozzle to vary the fan nozzle exit area and adjust the bypass ratio, and wherein the controller is an engine controller.

8. The turbofan engine as recited in claim 1 , wherein the fan variable area nozzle includes a plurality of sectors, and each of the plurality of sectors are simultaneously moveable.

9. The turbofan engine as recited in claim 1 , wherein the duct has a duct area distribution that is tailored such that the duct maximum area is greater than the fan nozzle exit area with the fan variable area nozzle in the fully open position.

10. The turbofan engine as recited in claim 1 , wherein the fan variable area nozzle has a maximum required effective area, and the fan nozzle exit area with the fan variable area nozzle in a fully open position is greater than the maximum required effective area of the fan variable area nozzle.

11. The turbofan engine as recited in claim 1 , wherein the fan variable area nozzle includes a first fan nacelle section, and a second fan nacelle section movably mounted relative the first fan nacelle section and moveable axially relative the first fan nacelle section.

12. The turbofan engine as recited in claim 11 , wherein axial movement of the second fan nacelle aection iclative to the first fan nacelle section defines an auxiliary port extending between the first fan nacelle section and the second fan nacelle section.

13. The turbofan engine as recited in claim 12 , wherein the second fan nacelle section defines a trailing edge of the fan variable area nozzle.

14. The turbofan engine as recited in claim 1 , wherein the fan variable area nozzle has an effective area increase limit, and the fan nozzle exit area has a maximum effective area increase, and the fan variable area nozzle to achieve the maximum effective area increase of the fan nozzle exit area in operation before the fan variable area nozzle has reached the effective area increase limit.

15. The turbofan engine as recited in claim 14 , wherein the duct has a duct area distribution and outer wall curvature that is tailored such that the maximum effective area increase of the fan nozzle exit area is achieved in operation before the fan variable area nozzle has reached the effective area increase limit.

16. The turbofan engine as recited in claim 14 , wherein the fan variable area nozzle includes a plurality of sectors, and each of the plurality of sectors are simultaneously moveable.

17. A turbofan engine comprising:

a fan section including a plurality of fan blades, the plurality of fan blades having a design angle of incidence;

a gear train including a planetary gear system having a gear reduction ratio of greater than 2.5:1;

a low pressure turbine driving the plurality of fan blades through the gear train, the low pressure turbine having a pressure ratio greater than 5:1;

a fan nacelle and a cure nacelle, the fan nacelle at least partially surrounding the core nacelle;

a fan bypass flow path defined between, the core nacelle and the fan nacelle, and a by-pass ratio greater than 10:1;

a fan variable area nozzle in communication with the fan bypass flow path, and defining a fan nozzle exit area between the fan nacelle and the core nacelle;

a controller in communication with the fan variable area nozzle;

a duct defined between the fan nacelle and the core nacelle forward of the fan variable area nozzle, the duct having a duct maximum area, wherein the duct maximum area is greater than the fan nozzle exit area with the fan variable area nozzle in a fully open position;

wherein the controller is configured to cause the fan variable area nozzle to vary the fan nozzle exit area in a plurality of flight conditions, causing the fan section to change to a more favorable fan operating line and avoid an instability region;

wherein the controller is configured to cause the fan variable nozzle to decreases the fan nozzle exit area for a cruise operating condition; and

wherein the controller is configured to cause the fan variable nozzle to increases the fan nozzle exit area for a landing operating condition.

18. The turbofan engine as recited in claim 17 , wherein the fan variable area nozzle includes a plurality of sectors, and each of the plurality of sectors are simultaneously moveable.

19. The turbofan engine as recited in claim 18 , further comprising a low spool including a low pressure compressor and the low pressure turbine, the low spool driving the planetary gear system, and wherein the plurality of fan blades include a fixed stagger angle.

20. The turbofan engine as recited in claim 19 , wherein the fan variable area nozzle varies the fan nozzle exit area to adjust fan bypass air flow in the fan bypass flow path in response to the controller in the plurality of flight conditions, maintaining an angle of incidence of the plurality of fan blades in the plurality of flight conditions that is close to the design angle of incidence on the plurality of fan blades.

21. The turbofan engine as recited in claim 17 , wherein the fan variable area nozzle has a maximum required effective area, and the fan nozzle exit area with the fan variable area nozzle in the fully open position is greater than the maximum required effective area of the fan variable area nozzle.

22. The turbofan engine as recited in claim 21 , further comprising a two stage high pressure turbine; and a low spool including a low pressure compressor and the low pressure turbine, the low spool driving the planetary gear system, and wherein the plurality of fan blades include a fixed stagger angle.

23. The turbofan engine as recited in claim 17 , wherein the fan variable area nozzle varies the fan nozzle exit area to adjust fan bypass air flow in the fan bypass flow path in response to the controller in the plurality of flight conditions, maintaining an angle of incidence of the plurality of fan blades in the plurality of flight conditions that is close to the design angle of incidence on the plurality of fan blades.

24. The turbofan engine as recited in claim 23 , wherein the fan variable area nozzle has an effective area increase limit, the fan nozzle exit area has a maximum effective area increase, and the fan variable area nozzle achieves the maximum effective area increase of the fan nozzle exit area in operation before the fan variable area nozzle has reached the effective area increase limit.