Flexible support structure for a geared architecture gas turbine engine

1. A geared architecture for a gas turbine engine comprising:

a fan shaft;

a frame which supports said fan shaft, said frame defines a frame stiffness;

a plurality of gears which drives said fan shaft;

a flexible support which supports the geared architecture and defines a flexible support stiffness that is less than said frame stiffness; and

an input coupling to said plurality of gears, said input coupling defines an input coupling stiffness which is less than said frame stiffness, wherein said flexible support stiffness and said input coupling stiffness are each less than about 20% of said frame stiffness.

2. The geared architecture as recited in claim 1 , wherein said frame and said flexible support are mounted to a static structure of a gas turbine engine.

3. The geared architecture as recited in claim 1 , wherein said input coupling is mounted to a sun gear of said gear system.

4. The geared architecture as recited in claim 3 , wherein said fan shaft is mounted to a ring gear of said gear system.

5. The geared architecture as recited in claim 4 , wherein said plurality of gears form a star system.

6. The geared architecture as recited in claim 3 , wherein said fan shaft is mounted to a planet carrier of said gear system.

7. The geared architecture as recited in claim 1 , wherein at least one of said flexible support stiffness and said input coupling stiffness are less than about 11% of said frame stiffness.

8. The geared architecture as recited in claim 7 , wherein said flexible support stiffness and said input coupling stiffness are each less than about 11% of said frame stiffness.

9. The geared architecture as recited in claim 1 , wherein said frame which supports said fan shaft and defines said frame stiffness is a K-frame bearing support, said K-frame bearing support supporting a bearing system that supports said fan shaft.

10. A geared architecture for a gas turbine engine comprising:

a fan shaft;

a frame which supports said fan shaft;

a plurality of gears which drives said fan shaft, said plurality of gears includes a gear mesh that defines a gear mesh stiffness;

a flexible support for supporting the geared architecture and which defines a flexible support stiffness that is less than said gear mesh stiffness, wherein said flexible support stiffness is less than about 8% of said gear mesh stiffness; and

an input coupling to said plurality of gears, said input coupling defines an input coupling stiffness with respect to said gear mesh stiffness, wherein said input coupling stiffness is less than about 5% of said gear mesh stiffness.

11. The geared architecture as recited in claim 10 , wherein a stiffness of a ring gear of said plurality of gears is less than about 20% of said gear mesh stiffness.

12. The geared architecture as recited in claim 11 , wherein at least one of a lateral stiffness and a transverse stiffness of a ring gear of said plurality of gears is less than about 12% of said gear mesh stiffness.

13. The geared architecture as recited in claim 12 , wherein at least one of a lateral stiffness and a transverse stiffness of a planet journal bearing which supports a planet gear of said plurality of gears is less than or equal to said gear mesh stiffness.

14. The geared architecture as recited in claim 10 , wherein said gear mesh stiffness is defined between a sun gear and a multiple planet gears of said plurality of gears.

15. The geared architecture as recited in claim 10 , wherein said plurality of gears floats with said fan shaft.

16. The geared architecture as recited in claim 10 , wherein a stiffness of a planet journal bearing which supports a planet gear of said plurality of gears is less than said gear mesh stiffness.

17. The geared architecture as recited in claim 10 , wherein a stiffness of a ring gear of said plurality of gears is less than said gear mesh stiffness.

18. A geared architecture for a gas turbine engine comprising:

a fan shaft;

a frame which supports said fan shaft, said frame defines a frame stiffness;

a plurality of gears which drives said fan shaft, said plurality of gears includes a gear mesh that defines a gear mesh stiffness;

a flexible support supporting the geared architecture and which defines a flexible support stiffness that is less than said gear mesh stiffness; and

an input coupling to said plurality of gears, said input coupling defines an input coupling stiffness that is less than said gear mesh stiffness, wherein said flexible support stiffness and said input coupling stiffness are each less than said frame stiffness.

19. The geared architecture as recited in claim 18 , wherein said flexible support stiffness and said input coupling stiffness are each less than about 20% of said frame stiffness.

20. The geared architecture as recited in claim 18 , wherein said flexible support stiffness is less than about 8% of said gear mesh stiffness.

21. The geared architecture as recited in claim 20 , wherein said input coupling stiffness is less than about 5% of said gear mesh stiffness.

22. The geared architecture as recited in claim 1 , wherein said flexible support supports a carrier of the geared architecture.

23. The geared architecture as recited in claim 1 , wherein said flexible support supports a ring gear of the geared architecture.

24. The geared architecture as recited in claim 10 , wherein said flexible support supports a carrier of the geared architecture.

25. The geared architecture as recited in claim 10 , wherein said flexible support supports a ring gear of the geared architecture.

26. The geared architecture as recited in claim 18 , wherein said flexible support supports a carrier of the geared architecture.

27. The geared architecture as recited in claim 18 , wherein said flexible support supports a ring gear of the geared architecture.