Flexible support structure for a geared architecture gas turbine engine

1. A gas turbine engine, comprising:

a drive shaft driving a propulsor;

a bypass duct at least partially defined by a housing outward of said propulsor;

a frame which supports said drive shaft, wherein said frame is a K-frame bearing support;

an epicyclic gear system connected to said drive shaft, said epicyclic gear system includes a sun gear having sun gear teeth, a plurality of planet gears having planet gear teeth, and a gear mesh between the sun gear teeth and the planet gear teeth, said gear mesh defining a gear mesh lateral stiffness and a gear mesh transverse stiffness, wherein a lateral stiffness refers to a perpendicular direction with respect to an axis of rotation of said gas turbine engine and a transverse stiffness refers to a pivotal bending movement with respect to said axis of rotation of said gas turbine engine;

an input coupling mounted to the sun gear of said epicyclic gear system;

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

wherein said flexible support lateral stiffness is less than 8% of said gear mesh lateral stiffness, said input coupling defining an input coupling lateral stiffness and an input coupling transverse stiffness, said frame defines a frame lateral stiffness and a frame transverse stiffness, and said input lateral stiffness is less than 11% of said frame lateral stiffness.

2. The gas turbine engine of claim 1 , further comprising a two stage high pressure turbine.

3. The gas turbine engine of claim 1 , wherein said drive shaft is mounted to a ring gear of said epicyclic gear system.

4. The gas turbine engine of claim 1 , wherein said drive shaft is mounted to a planet carrier of said epicyclic gear system.

5. The gas turbine engine of claim 1 , wherein said drive shaft is mounted to a ring gear of said epicyclic gear system.

6. The gas turbine engine of claim 1 , wherein said drive shaft is mounted to a planet carrier of said epicyclic gear system.

7. The gas turbine engine of claim 1 , wherein said input coupling transverse stiffness is less than 11% of said frame transverse stiffness.

8. The gas turbine engine of claim 7 , further comprising a two stage high pressure turbine.

9. The gas turbine engine of claim 1 , wherein said input coupling lateral stiffness is less than 5% of said gear mesh lateral stiffness.

10. The gas turbine engine of claim 9 , wherein said input coupling transverse stiffness is less than 5% of said gear mesh transverse stiffness.

11. The gas turbine engine of claim 10 , wherein gear system includes a ring gear having a stiffness that is less than 20% of said gear mesh.

12. A gas turbine engine, comprising:

a drive shaft driving a propulsor;

a frame supporting said drive shaft, wherein said frame is a K-frame bearing support;

a gear system connected to said drive shaft and driven through an input, wherein said gear system includes a ring gear, a sun gear having sun gear teeth, a plurality of planet gears having planet gear teeth, and a gear mesh between the sun gear teeth and the planet gear teeth, said gear mesh defines a gear mesh lateral stiffness and a gear mesh transverse stiffness, and said ring gear defining a ring gear lateral stiffness;

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

wherein said flexible support transverse stiffness is less than 8% of said gear mesh transverse stiffness, and said ring gear lateral stiffness is less than 12% of said gear mesh lateral stiffness.

13. The gas turbine engine of claim 12 , further comprising a two stage high pressure turbine and a bypass duct at least partially defined by a housing outward of said propulsor.

14. The gas turbine engine of claim 12 , wherein said drive shaft is mounted to the ring gear.

15. The gas turbine engine of claim 12 , wherein drive shaft is mounted to a planet carrier of said gear system.

16. A gas turbine engine, comprising:

a drive shaft driving a propulsor;

a frame supporting said drive shaft;

a gear system connected to said drive shaft and driven through an input wherein said input to said gear system and said gear system defines a gear mesh lateral stiffness and a gear mesh transverse stiffness;

a journal bearing defining a journal bearing transverse stiffness that is less than said gear mesh transverse stiffness; and

a gear system flex mount arrangement, wherein said flex mount arrangement accommodates misalignment of said drive shaft and said input during operation and includes a flexible support defining a flexible support lateral stiffness and a flexible support transverse stiffness, said flexible support lateral stiffness is less than 8% of said gear mesh lateral stiffness, said flexible support transverse stiffness is less than 8% of said gear mesh transverse stiffness, said frame defines a frame lateral stiffness and said flexible support lateral stiffness is less than 11% of said frame lateral stiffness, said frame defines a frame transverse stiffness and said flexible support transverse stiffness is less than 11% of said frame transverse stiffness, and said gear system includes a ring gear defining a ring gear lateral stiffness that is less than 12% of said gear mesh lateral stiffness.

17. The gas turbine engine of claim 16 , further comprising a two stage high pressure turbine.

18. The gas turbine engine of claim 17 , wherein a ring gear of said gear system defines a ring gear transverse stiffness and said ring gear transverse stiffness is less than 12% of said gear mesh transverse stiffness.

19. The gas turbine engine of claim 17 , further comprising a bypass duct at least partially defined by a housing outward of said propulsor.

20. The gas turbine engine of claim 19 , wherein said gear system is an epicyclic gear system and said drive shaft is mounted to a ring gear of said epicyclic gear system.

21. The gas turbine engine of claim 19 , wherein said gear system is an epicyclic gear system and said drive shaft is mounted to a planet carrier of said epicyclic gear system.