Flexible support structure for a geared architecture gas turbine engine

Abstract

A gas turbine engine according to an example of the present disclosure includes, among other things, a fan shaft driving a fan having fan blades, a fan shaft support supporting the fan shaft. A gear system connected to the fan shaft includes a ring gear defining a ring gear transverse stiffness, a gear mesh defining a gear mesh lateral stiffness, and a gear mesh transverse stiffness. The gear system also includes a reduction ratio greater than 2.3. A gear system input to the gear system defines a gear system input lateral stiffness. The ring gear transverse stiffness is less than 20% of the gear mesh transverse stiffness and the gear system input lateral stiffness is less than 5% of said gear mesh lateral stiffness.

What is claimed is: 
     
         1 . 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 ring gear defining a ring gear transverse stiffness, a gear mesh defining a gear mesh lateral stiffness and a gear mesh transverse stiffness, and a reduction ratio greater than 2.3;   a gear system input to said gear system, said gear system input defines a gear system input lateral stiffness; and   wherein said ring gear transverse stiffness is less than 20% of said gear mesh transverse stiffness and 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 fan shaft support defines a fan shaft support transverse stiffness, 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. 
     
     
         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. 
     
     
         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 ring gear defining a ring gear lateral stiffness, a gear mesh defining a gear mesh lateral stiffness, and a reduction ratio greater than 2.3; and   wherein said ring gear lateral stiffness is less than 12% of said gear mesh lateral 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. 
     
     
         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. 
     
     
         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 , wherein said ring gear defines a ring gear transverse stiffness, said gear mesh defines a gear mesh transverse stiffness, and said ring gear transverse stiffness is less than 12% of said gear mesh transverse stiffness. 
     
     
         17 . The gas turbine engine of  claim 16 , further comprising a flexible support which supports said gear system and defines a flexible support lateral stiffness and said flexible support lateral stiffness is less than 8% of said gear mesh lateral stiffness. 
     
     
         18 . The gas turbine engine of  claim 17 , wherein said flexible support includes a flexible support transverse stiffness and said flexible support transverse stiffness is less than 8% of said gear mesh transverse stiffness. 
     
     
         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 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.