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 lateral stiffness and a fan shaft support transverse stiffness;

a gear system connected to said fan shaft including a reduction ratio of greater than 2.3;

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

a low fan pressure ratio of less than 1.45 and said low fan pressure ratio is measured across the fan blades alone; and

wherein at least one of 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 20% of said fan shaft support transverse stiffness.

2 . The gas turbine engine of claim 1 , wherein said gear system includes a gear mesh defining a gear mesh transverse stiffness and said flexible support transverse stiffness is less than 8% of said gear mesh transverse stiffness.

3 . The gas turbine engine of claim 2 , 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, wherein the gear system is a planetary gear system and said flexible support lateral is less than 11% of said fan shaft support lateral stiffness.

4 . The gas turbine engine of claim 3 , 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 and said flexible transverse stiffness is less than 11% of said fan shaft support transverse stiffness.

5 . The gas turbine engine of claim 4 , further comprising a bypass ratio greater than ten (10) and a two stage high pressure turbine and wherein said gear system includes a gear mesh defining a gear mesh lateral stiffness and said flexible support lateral stiffness is less than 8% of said gear mesh lateral stiffness.

6 . The gas turbine engine of claim 5 , 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 11% of said fan shaft support lateral stiffness.

7 . The gas turbine engine of claim 2 , wherein the flexible support transverse stiffness is less than 11% of said fan shaft support transverse stiffness.

8 . The gas turbine engine of claim 7 , wherein said gear mesh defines a gear mesh lateral stiffness and said flexible support lateral stiffness is less than 8% of said gear mesh lateral stiffness.

9 . The gas turbine engine of claim 3 , further comprising a bypass ratio greater than 10 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 flexible lateral stiffness is less than 11% of said fan shaft support lateral stiffness, and said gear system is a planetary gear system.

10 . The gas turbine engine of claim 9 , further comprising a two stage high pressure turbine, an inner shaft and an outer shaft concentric with said inner shaft that both rotate via at least one bearing system, and 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.

11 . The gas turbine engine of claim 10 , 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 11% of said fan shaft support lateral stiffness.

12 . The gas turbine engine of claim 1 , further comprising a gear system input to said gear system defining a gear system input lateral stiffness 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 input lateral stiffness is less than 11% of said fan shaft support lateral stiffness.

13 . The gas turbine engine of claim 12 , further comprising a two stage high pressure turbine, and 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, wherein the gear system is a planetary gear system and said gear system defines a gear system input transverse stiffness and said gear system input transverse stiffness and is less than 11% of said fan shaft support transverse stiffness.

14 . 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 lateral stiffness and a fan shaft support transverse stiffness;

a gear system connected to said fan shaft including a reduction ratio of greater than 2.3;

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

a mid-turbine frame;

a low fan pressure ratio of less than 1.45 and said low fan pressure ratio is measured across the fan blades alone; and

wherein at least one of 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 20% of said fan shaft support transverse stiffness.

15 . The gas turbine engine of claim 14 , wherein said flexible support lateral stiffness is less than 11% of said fan shaft support lateral stiffness.

16 . The gas turbine engine of claim 15 , wherein said gear system includes a gear mesh defining a gear mesh lateral stiffness and said flexible support lateral stiffness is less than 8% of said gear mesh lateral stiffness.

17 . The gas turbine engine of claim 16 , 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 and said gear mesh defines a gear mesh transverse stiffness and said flexible support transverse stiffness is less than 8% of said gear mesh transverse stiffness.

18 . The gas turbine engine of claim 17 , further comprising a bypass ratio greater than ten (10), wherein the gear system is a planetary gear system and said flexible support transverse stiffness is less than 11% of said fan shaft support transverse stiffness.

19 . The gas turbine engine of claim 18 , further comprising a two stage high pressure turbine, and 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.

20 . The gas turbine engine of claim 18 , further comprising an inner shaft and an outer shaft concentric with said inner shaft that both rotate via at least one bearing system, wherein said mid-turbine frame includes at least one airfoil extending into a flow path.

21 . 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 lateral stiffness and a fan shaft support transverse stiffness;

a gear system connected to said fan shaft including a gear mesh defining a gear mesh transverse stiffness and a reduction ratio of greater than 2.3;

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

a low fan pressure ratio of less than 1.45 and said low fan pressure ratio is measured across the fan blades alone; and

wherein said flexible support lateral stiffness is less than 11% of said fan shaft support lateral stiffness, said flexible support transverse stiffness is less than 20% of said fan shaft support transverse stiffness, and said flexible support transverse stiffness is less than 8% of said gear mesh transverse stiffness.

22 . The gas turbine engine of claim 21 , 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 and said gear mesh defines a gear mesh lateral stiffness and the flexible support lateral stiffness is less than 8% of said gear mesh lateral stiffness.

23 . The gas turbine engine of claim 22 , further comprising a two stage high pressure turbine and a bypass ratio greater than ten (10), wherein the gear system is a planetary gear system.

24 . The gas turbine engine of claim 22 , further comprising:

a three stage low pressure compressor; and

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.

25 . The gas turbine engine of claim 22 , further comprising a mid-turbine frame including at least one airfoil extending into a flow path.

26 . The gas turbine engine of claim 25 , further comprising:

a three stage low pressure compressor;

an inner shaft and an outer shaft concentric with said inner shaft that both rotate via at least one bearing system;

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 mid-turbine frame includes at least one airfoil extending into a flow path.

27 . The gas turbine engine of claim 22 , 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 11% of said fan shaft support lateral stiffness.

28 . The gas turbine engine of claim 21 , 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.

29 . The gas turbine engine of claim 28 , further comprising a gear system input to said gear system defining a gear system input lateral stiffness and said gear system input lateral stiffness is less than 11% of said fan shaft support lateral stiffness.

30 . The gas turbine engine of claim 29 , further comprising:

a two stage high pressure turbine;

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 gear system is a planetary gear system and said gear system defines a gear system input transverse stiffness and said gear system input transverse stiffness is less than 11% of said fan shaft support transverse stiffness.