Flexible support structure for a geared architecture gas turbine engine

1. A gas turbine engine, comprising:

a fan shaft driving a fan having fan blades;

a fan shaft support that supports said fan shaft defining a fan shaft support transverse stiffness;

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 connected to said gear system, said gear system input defines a gear system input lateral stiffness;

a flexible support supporting said gear system and defining a flexible support transverse stiffness; and

wherein said gear system input lateral stiffness is less than 5% of said gear mesh lateral stiffness.

2. The gas turbine engine of claim 1 , wherein said gear system input defines a gear system input transverse stiffness, and said gear system input transverse stiffness is less than 5% of said gear mesh transverse stiffness.

3. The gas turbine engine of claim 2 , wherein said gear system input transverse stiffness is less than 20% of said fan shaft support transverse stiffness.

4. The gas turbine engine of claim 3 , wherein said gear system input transverse stiffness is less than 11% of said fan shaft support transverse stiffness.

5. The gas turbine engine of claim 1 , further comprising a low fan pressure ratio of less than about 1.45 and said low fan pressure ratio measured across the fan blades alone, and wherein said gear system includes a reduction ratio greater than 2.3.

6. The gas turbine engine of claim 5 , further comprising a two stage high pressure turbine and a low pressure turbine with an inlet, an outlet, and a low pressure turbine pressure ratio greater than about 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.

7. The gas turbine engine of claim 6 , wherein said gear system input defines a gear system input transverse stiffness and said gear system input transverse stiffness is less than 5% of said gear mesh transverse stiffness, and said flexible support transverse stiffness is less than 20% of said fan shaft support transverse stiffness.

8. The gas turbine engine of claim 7 , further comprising a low corrected fan tip speed less than about 1150 ft/second, wherein said low corrected fan tip speed is an actual fan tip speed at an ambient temperature divided by [(T ram ° R)/(518.7° R)] 0.5 , where T represents said ambient temperature in degrees Rankine.

9. A gas turbine engine, comprising:

a fan shaft driving a fan having fan blades;

a fan shaft support that supports 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 flexible support supporting said gear system and defining a flexible support lateral stiffness and a flexible support transverse stiffness; and

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.

10. The gas turbine engine of claim 9 , further comprising a low fan pressure ratio of less than about 1.45, said low fan pressure ratio measured across the fan blades alone, and wherein said gear system includes a reduction ratio greater than 2.3.

11. The gas turbine engine of claim 10 , further comprising a low pressure turbine with an inlet, an outlet, and a low pressure turbine pressure ratio greater than about 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.

12. The gas turbine engine of claim 11 , further comprising a low corrected fan tip speed less than about 1150 ft/second, wherein said low corrected fan tip speed is an actual fan tip speed at an ambient temperature divided by [(T ram ° R)/(518.7° R)] 0.5 , where T represents said ambient temperature in degrees Rankine.

13. The gas turbine engine of claim 11 , further comprising a bypass ratio greater than ten (10).

14. The gas turbine engine of claim 9 , further comprising a low pressure turbine with an inlet, an outlet, and a low pressure turbine pressure ratio greater than about 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, and wherein said gear system includes a reduction ratio greater than 2.3.

15. The gas turbine engine of claim 9 , further comprising a low corrected fan tip speed less than about 1150 ft/second, wherein said low corrected fan tip speed is an actual fan tip speed at an ambient temperature divided by [(T ram ° R)/(518.7° R)] 0.5 , where T represents said ambient temperature in degrees Rankine.

16. The gas turbine engine of claim 9 , further comprising a ring gear defining a ring gear transverse stiffness and said ring gear transverse stiffness is less than 20% of said gear mesh transverse stiffness.

17. The gas turbine engine of claim 16 , wherein both said flexible support lateral stiffness and said flexible support transverse stiffness are less than 8% of a respective one of said gear mesh lateral stiffness and said gear mesh transverse stiffness.

18. The gas turbine engine of claim 17 , further comprising a low fan pressure ratio of less than about 1.45, said low fan pressure ratio measured across the fan blades alone, and wherein said gear system includes a reduction ratio greater than 2.3.

19. The gas turbine engine of claim 18 , wherein said fan shaft support defines a fan shaft support lateral stiffness and said flexible support lateral stiffness is less than 11% of said fan shaft support lateral stiffness.

20. The gas turbine engine of claim 19 , wherein said flexible support defines a flexible support transverse stiffness and said fan shaft support defines a fan shaft support transverse stiffness and said flexible support transverse stiffness is less than 20% of said fan shaft support transverse stiffness.

21. The gas turbine engine of claim 20 , wherein said flexible support lateral stiffness is less than 11% of said fan shaft support lateral stiffness and said flexible support transverse stiffness is less than 11% of said fan shaft support transverse stiffness.

22. The gas turbine engine of claim 20 , further comprising a gear system input to said gear system, said gear system input defines a gear system input lateral stiffness, wherein said gear system input lateral stiffness is less than 20% of said fan shaft support lateral stiffness.

23. The gas turbine engine of claim 22 , wherein said gear system input defines a gear system input transverse stiffness and said gear system input transverse stiffness is less than 20% of said fan shaft support transverse stiffness.

24. The gas turbine engine of claim 23 , wherein said gear system input lateral stiffness is less than 11% of said fan shaft support lateral stiffness.

25. The gas turbine engine of claim 24 , wherein said gear system input transverse stiffness is less than 11% of said fan shaft support transverse stiffness.

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

27. The gas turbine engine of claim 20 , further comprising a gear system input to said gear system defining a gear system input lateral stiffness, wherein said gear system input lateral stiffness is less than 5% of said gear mesh lateral stiffness.

28. The gas turbine engine of claim 27 , wherein said gear system input defines a gear system input transverse stiffness and said gear system input transverse stiffness is less than 5% of said gear mesh transverse stiffness and said gear system input both transfers torque and facilitates segregation of vibrations.

29. The gas turbine engine of claim 20 , further comprising a low pressure turbine with an inlet, an outlet, and a low pressure turbine pressure ratio greater than about 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 and a low fan pressure ratio of less than about 1.45 with said low fan pressure ratio measured across the fan blades alone.

30. The gas turbine engine of claim 29 , further comprising a low corrected fan tip speed less than about 1150 ft/second, wherein said low corrected fan tip speed is an actual fan tip speed at an ambient temperature divided by [(T ram ° R)/(518.7° R)] 0.5 , where T represents said ambient temperature in degrees Rankine.

31. The gas turbine engine of claim 9 wherein said flexible support transverse stiffness is less than 8% of said gear mesh transverse stiffness.

32. The gas turbine engine of claim 31 , further comprising a bypass ratio greater than ten (10) and said gear system includes a reduction ratio greater than 2.3.

33. The gas turbine engine of claim 32 , further comprising 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.

34. The gas turbine engine of claim 33 , further comprising a two stage high pressure turbine.

35. The gas turbine engine of claim 34 , wherein said flexible support is mounted to an engine static structure.

36. The gas turbine engine of claim 32 , further comprising a low corrected fan tip speed less than about 1150 ft/second, wherein said low corrected fan tip speed is an actual fan tip speed at an ambient temperature divided by [(Tram ° R)/(518.7 ° R)]0.5, where T represents said ambient temperature in degrees Rankine.

37. The gas turbine engine of claim 32 , further comprising a gear system input to said gear system defining a gear system input transverse stiffness and said fan shaft support defining a fan shaft support transverse stiffness, wherein said gear system input transverse stiffness is less than 20% of said fan shaft support transverse stiffness.

38. The gas turbine engine of claim 37 , wherein said flexible support is mounted to an engine static structure.

39. The gas turbine engine of claim 38 , further comprising a mid-turbine frame including at least one airfoil extending into a flow path, and wherein said fan shaft support is a K-frame bearing support.

40. The gas turbine engine of claim 37 , wherein said gear mesh defines a gear mesh lateral stiffness and said gear system input defines a gear system input lateral stiffness and said gear system input lateral stiffness is less than 5% of said gear mesh lateral stiffness.

41. The gas turbine engine of claim 40 , wherein said fan shaft support defines a fan shaft support lateral stiffness and said gear system input lateral stiffness is less than 11% of said fan shaft support lateral stiffness.

42. The gas turbine engine of claim 37 , further comprising a two stage high pressure turbine and a low fan pressure ratio of less than 1.45 and said low fan pressure ratio is measured across the fan blades alone.

43. The gas turbine engine of claim 42 , further comprising 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.

44. The gas turbine engine of claim 43 , wherein said gear system input transverse stiffness is less than 11% of said fan shaft support transverse stiffness.

45. The gas turbine engine of claim 43 , further comprising a low corrected fan tip speed less than about 1150 ft/second, wherein said low corrected fan tip speed is an actual fan tip speed at an ambient temperature divided by [(Tram ° R)/(518.7 ° R)]0.5, where T represents said ambient temperature in degrees Rankine.

46. The gas turbine engine of claim 45 , wherein said gear system input transverse stiffness is less than 11% of said fan shaft support transverse stiffness, and said gear system input both transfers torque and facilitates segregation of vibrations.

47. The gas turbine engine of claim 31 , further comprising a two stage high pressure turbine, a low fan pressure ratio of less than 1.45 and said low fan pressure ratio is measured across the 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 and said gear system includes a reduction ratio greater than 2.3.

48. The gas turbine engine of claim 47 , further comprising a low corrected fan tip speed less than about 1150 ft/second, wherein said low corrected fan tip speed is an actual fan tip speed at an ambient temperature divided by [(Tram ° R)/(518.7 ° R)]0.5, where T represents said ambient temperature in degrees Rankine, and wherein said flexible support is mounted to an engine static structure.

49. The gas turbine engine of claim 48 , further comprising an input coupling to said gear system defining an input coupling lateral stiffness, wherein said fan shaft support defines a fan shaft support lateral stiffness and said input coupling lateral stiffness is less than 11% of said fan shaft support lateral stiffness.

50. The gas turbine engine of claim 9 , further comprising a ring gear defines a ring gear lateral stiffness, wherein said gear mesh defines a gear mesh lateral stiffness, and said flexible support defines a flexible support lateral stiffness and said flexible support lateral stiffness is less than 8% of said gear mesh lateral stiffness and said ring gear lateral stiffness is less than 12% of said gear mesh lateral stiffness.