Geared architecture for high speed and small volume fan drive turbine

Abstract

A gas turbine engine includes a fan shaft that has fan blades. A fan shaft is drivingly connected to the fan. A fan shaft support supports the fan shaft and defines a fan shaft support lateral stiffness. A gear system is connected to the fan shaft and driven through an input. A gear system flex mount arrangement accommodates misalignment of the fan shaft and the input during operation and includes a flexible support that defines a flexible support lateral stiffness that is less than 11% of the shaft support lateral stiffness.

What is claimed is: 
     
         1 . A gas turbine engine, comprising:
 a fan shaft drivingly connected to a fan, said fan having fan blades;   a fan shaft support supporting said fan shaft and defining a fan shaft support lateral stiffness;   a gear system connected to said fan shaft and driven through an input; and   a gear system flex mount arrangement, wherein said flex mount arrangement accommodates misalignment of said fan shaft and said input during operation, and includes a flexible support defining a flexible support lateral stiffness that is less than 11% of said shaft support lateral stiffness.   
     
     
         2 . The gas turbine engine of  claim 1 , further comprising a ring gear defining a ring gear lateral stiffness and a gear mesh defining a gear mesh lateral stiffness and said ring gear lateral stiffness is less than 12% of said gear mesh lateral stiffness. 
     
     
         3 . The gas turbine engine of  claim 2 , wherein said flexible support lateral stiffness is less than 8% of said gear mesh lateral stiffness. 
     
     
         4 . The gas turbine engine of  claim 3 , wherein said gear system has a gear reduction ratio of greater than 2.3, and further comprising a bypass ratio greater than ten (10), a low 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 1 , further comprising a gear mesh defining a gear mesh lateral stiffness, wherein said flexible support lateral stiffness is less than 8% of said gear mesh lateral stiffness. 
     
     
         6 . The gas turbine engine of  claim 5 , wherein said gear system has a gear reduction ratio of greater than 2.3, and further comprising a bypass ratio greater than ten (10), a low fan pressure ratio of less than 1.45 measured across said fan blades alone, 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 a mid-turbine frame including a bearing support structure supporting a bearing system. 
     
     
         7 . The gas turbine engine of  claim 6 , further comprising a core flow path, a fan tip speed of less than 1150 ft/second and said mid-turbine frame includes at least one airfoil in said core flow path and directing air flow around said bearing support structure. 
     
     
         8 . The gas turbine engine of  claim 5 , further comprising a bypass ratio greater than ten (10), a low 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, said flexible support defines a flexible support transverse stiffness and said fan shaft support defines a fan shaft support transverse stiffness with said flexible support transverse stiffness less than 11% of said fan shaft support transverse stiffness, and said gear system has a gear reduction ratio of greater than 2.3, and a gear mesh defines a gear mesh transverse stiffness with said flexible support transverse stiffness less than 8% of said gear mesh transverse stiffness. 
     
     
         9 . The gas turbine engine of  claim 1 , wherein said gear system has a gear reduction ratio of greater than 2.3, and further comprising a bypass ratio greater than ten (10), a low fan pressure ratio of less than 1.45 and said low fan pressure ratio is 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. 
     
     
         10 . The gas turbine engine of  claim 9 , wherein a gear mesh defines a gear mesh lateral stiffness and said flexible support lateral stiffness less than 8% of said gear mesh lateral stiffness. 
     
     
         11 . The gas turbine engine of  claim 10 , wherein said input defines an input lateral stiffness that is less than 11% of said fan shaft support lateral stiffness. 
     
     
         12 . The gas turbine engine of  claim 11 , wherein said gear system includes a ring gear defining a ring gear lateral stiffness and said ring gear lateral stiffness is less than 12% of said gear mesh lateral stiffness. 
     
     
         13 . The gas turbine engine of  claim 10 , 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 11% of said fan shaft support transverse stiffness. 
     
     
         14 . The gas turbine engine of  claim 1 , wherein said gear system has a gear reduction ratio of greater than 2.3, and further comprising a bypass ratio greater than ten (10), a low fan pressure ratio of less than 1.45 and said low fan pressure ratio is measured across said fan blades alone, and a gear mesh defines a gear mesh lateral stiffness and said flexible support lateral stiffness is less than 8% of said gear mesh lateral stiffness. 
     
     
         15 . The gas turbine engine of  claim 14 , 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 11% of said fan shaft support transverse stiffness. 
     
     
         16 . The gas turbine engine of  claim 1 , wherein said gear system has a gear reduction ratio of greater than 2.3, and further comprising a bypass ratio greater than ten (10), a low fan pressure ratio of less than 1.45 and said low fan pressure ratio is measured across said fan blades alone, and 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 11% of said fan shaft support transverse stiffness. 
     
     
         17 . A gas turbine engine comprising:
 a fan shaft drivingly connected to a fan, said fan having fan blades;   a gear system connected to said fan shaft and driven through an input, a gear system flex mount arrangement, wherein the flex mount arrangement accommodates misalignment of said fan shaft and said input during operation, and a ring gear defining a ring gear lateral stiffness and a gear mesh defining a gear mesh lateral stiffness, wherein said ring gear lateral stiffness is less than 12% of said gear mesh lateral stiffness.   
     
     
         18 . The gas turbine engine of  claim 17 , wherein said gear system has a gear reduction ratio of greater than 2.3, and further comprising a bypass ratio greater than ten (10), a low fan pressure ratio of less than 1.45 and said low fan pressure ratio is 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. 
     
     
         19 . The gas turbine engine of  claim 18 , further comprising a mid-turbine frame supporting a bearing system and having at least one airfoil in a core flow path. 
     
     
         20 . The gas turbine engine of  claim 19 , wherein said flex mount arrangement includes a flexible support defining a flexible support lateral stiffness, 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. 
     
     
         21 . The gas turbine engine of  claim 18 , wherein said flex mount arrangement includes a flexible support defining a flexible support lateral stiffness, 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. 
     
     
         22 . The gas turbine engine of  claim 21 , further comprising a fan shaft support that supports said fan shaft and defines a fan shaft support lateral stiffness, wherein said input defines an input lateral stiffness that is less than 11% of said fan shaft support lateral stiffness. 
     
     
         23 . The gas turbine engine of  claim 22 , wherein said flexible support lateral stiffness is less than 8% of said gear mesh lateral stiffness. 
     
     
         24 . The gas turbine engine of  claim 23 , wherein said ring gear defines a ring gear transverse stiffness and 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. 
     
     
         25 . The gas turbine engine of  claim 24 , further comprising a fan shaft support that supports said fan shaft defining a fan shaft support transverse stiffness, wherein said input defines an input transverse stiffness, said fan shaft support define a fan shaft support transverse stiffness, and said input transverse stiffness is less than 11% of said fan shaft support transverse stiffness. 
     
     
         26 . The gas turbine engine of  claim 25 , further comprising a fan tip speed of less than 1150 ft/second and a mid-turbine frame including at least one airfoil in a core flow path. 
     
     
         27 . A gas turbine engine comprising
 a fan shaft drivingly connected to a fan, said fan having fan blades;   a fan shaft support that supports said fan shaft defining a fan shaft support lateral stiffness;   a gear system connected to said fan shaft and driven through an input, said input defining an input lateral stiffness that is less than  11  % of said fan shaft support lateral stiffness; and   a gear system flex mount arrangement, wherein said flex mount arrangement accommodates misalignment of said fan shaft and said input during operation.   
     
     
         28 . The gas turbine engine of  claim 27 , wherein said flex mount arrangement includes a flexible support defining a flexible support lateral stiffness that is less than 11% of said fan shaft support lateral stiffness. 
     
     
         29 . The gas turbine engine of  claim 28 , further comprising a ring gear defining a ring gear lateral stiffness, a gear mesh defining a gear mesh lateral stiffness, and said ring gear lateral stiffness is less than 12% of said gear mesh lateral stiffness. 
     
     
         30 . The gas turbine engine of  claim 29 , wherein said gear system has a gear reduction ratio of greater than 2.3, and further comprising a gear reduction ratio of greater than 2.3, a bypass ratio greater than ten (10), a low 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 and said flexible support lateral stiffness is less than 8% of said gear mesh lateral stiffness.