Flexible support structure for a geared architecture gas turbine engine

1. A gas turbine engine, comprising:

a fan having fan blades;

an outer housing surrounding the fan, and a bypass flow path within said outer housing;

a fan shaft drivingly connected to said fan;

a frame supporting said fan shaft and defining a frame lateral stiffness and a frame transverse stiffness;

a gear system connected to said fan shaft and driven through an input defining an input lateral stiffness and an input transverse stiffness, said gear system includes a gear mesh defining a gear mesh lateral stiffness and a gear mesh transverse stiffness; and

a gear system flex mount arrangement, wherein said gear system flex mount arrangement accommodates misalignment of said fan shaft and said input during operation and includes a flexible support which supports said gear system relative to a static structure and defines a flexible support lateral stiffness and a flexible support transverse stiffness;

wherein at least one of said flexible support lateral stiffness and said flexible support transverse stiffness is less than 8% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness; and

wherein at least one of said input lateral stiffness and said input transverse stiffness is less than 11% of a respective one of said frame lateral stiffness and said frame transverse stiffness.

2. The gas turbine engine of claim 1 , wherein at least one of said flexible support lateral stiffness and said flexible support transverse stiffness is less than 11% of a respective one of said frame lateral stiffness and said frame transverse stiffness.

3. The gas turbine engine of claim 2 , wherein at least one of said input lateral stiffness and said input transverse stiffness is less than 5% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness.

4. The gas turbine engine of claim 3 , further comprising a gear reduction ratio of greater than 2.3, a bypass ratio greater than ten (10), a fan pressure ratio of less than 1.45 measured across said fan blades alone, and a low pressure turbine with an inlet, an outlet, and a low pressure turbine pressure ratio greater than 5:1, wherein said low pressure turbine pressure ratio is a ratio of a pressure measured prior to said inlet as related to a pressure at said outlet prior to any exhaust nozzle.

5. The gas turbine engine of claim 4 , wherein said gear system includes a ring gear defining a ring gear lateral stiffness that is less than 12% of said gear mesh lateral stiffness.

6. The gas turbine engine of claim 4 , wherein said gear system includes a ring gear defining a ring gear transverse stiffness that is less than 12% of said gear mesh transverse stiffness.

7. The gas turbine engine of claim 4 , wherein said gear system includes a ring gear defining a ring gear lateral stiffness and a ring gear transverse stiffness and said ring gear lateral stiffness and said ring gear transverse stiffness are less than 12% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness.

8. The gas turbine engine of claim 4 , further comprising a two stage high pressure turbine.

9. The gas turbine engine of claim 8 , further comprising a three stage low pressure compressor.

10. The gas turbine engine of claim 9 , further comprising a fan tip speed of less than 1150 ft/second.

11. The gas turbine engine of claim 4 , further comprising a journal bearing defining a journal bearing lateral stiffness that is less than said gear mesh lateral stiffness.

12. A gas turbine engine, comprising:

a fan having fan blades;

an outer housing surrounding the fan, and a bypass flow path within said outer housing;

a fan shaft drivingly connected to said fan;

a frame supporting said fan shaft;

a gear system connected to said fan shaft, said gear system includes a gear mesh defining a gear mesh lateral stiffness and a gear mesh transverse stiffness;

a gear system input to said gear system defining a gear system input lateral stiffness and a gear system input transverse stiffness; and

wherein at least one of said gear system input lateral stiffness and said gear system input transverse stiffness is less than 5% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness.

13. The gas turbine engine of claim 12 , further comprising a low fan pressure ratio of less than 1.45 and said low fan pressure ratio is measured across the fan blades alone.

14. The gas turbine engine of claim 13 , further comprising a fan tip speed less than about 1150 ft/second.

15. The gas turbine engine of claim 14 , further comprising a mid-turbine frame including at least one airfoil extending into a flow path.

16. The gas turbine engine of claim 15 , further comprising a bypass ratio greater than ten (10).

17. The gas turbine engine of claim 16 , wherein said gear system input transverse stiffness is less than 5% of said gear mesh transverse stiffness.

18. The gas turbine engine of claim 17 , further comprising a ring gear in said gear system defining a ring gear lateral stiffness, wherein said ring gear lateral stiffness is less than 12% of said gear mesh lateral stiffness.

19. The gas turbine engine of claim 16 , wherein said gear system input lateral stiffness is less than 5% of said gear mesh lateral stiffness.

20. The gas turbine engine of claim 19 , further comprising a ring gear in said gear system defining a ring gear lateral stiffness, wherein the ring gear lateral stiffness is less than 12% of said gear mesh lateral stiffness.

21. The gas turbine engine of claim 12 , wherein said frame defines a frame lateral stiffness and a frame transverse stiffness, at least one of said gear system input lateral stiffness and said gear system input transverse stiffness is less than 11% of a respective one of said frame lateral stiffness and said frame transverse stiffness.

22. The gas turbine engine of claim 21 , wherein said gear system input transverse stiffness is less than 11% of said frame transverse stiffness.

23. The gas turbine engine of claim 22 , wherein said gear system input transverse stiffness is less than 5% of said gear mesh transverse stiffness.

24. The gas turbine engine of claim 23 , wherein said gear system input lateral stiffness is less than 5% of said gear mesh lateral stiffness.

25. The gas turbine engine of claim 24 , further comprising a fan tip speed less than about 1150 ft/second.

26. The gas turbine engine of claim 25 , further comprising a ring gear in said gear system defining a ring gear lateral stiffness and a ring gear transverse stiffness, wherein at least one of said ring gear lateral stiffness and said ring gear transverse stiffness is less than 12% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness.

27. The gas turbine engine of claim 26 , wherein said ring gear lateral stiffness is less than 12% of said gear mesh lateral stiffness.

28. The gas turbine engine of claim 21 , wherein said gear system input lateral stiffness is less than 5% of said gear mesh lateral stiffness.

29. The gas turbine engine of claim 12 , further comprising a two stage high pressure turbine.

30. The gas turbine engine of claim 29 , further comprising a three stage low pressure compressor.