Geared Turbofan With Fan Blades Designed To Achieve Laminar Flow

Abstract

A fan blade comprises a main body having an airfoil extending between a leading edge and a trailing edge. The fan blade has at least one of a channel closed by a cover, and an end cap covering at least one of the leading and trailing edges. At least one of a cover and an end cap has a pair of opposed ends. A step is defined extending from at least one of a suction wall and a pressure wall of the airfoil, to an outer surface of the one of a cover and an end cap at one of the opposed ends, and the step being less than or equal to about 0.010 inch (0.0254 centimeter) in dimension.

1 . A fan blade comprising:
 a main body having an airfoil extending between a leading edge and a trailing edge and the fan blade having at least one of:   (a) a channel closed by a cover, and   (b) an end cap covering at least one of the leading and trailing edges; and   the at least one of the cover and the end cap having a pair of opposed ends, and a step defined by at least one of a suction wall and a pressure wall of the airfoil, to an outer surface of said one of the cover and the end cap at one of said opposed ends, and said step being less than or equal to about 0.010 inch (0.0254 centimeter) in dimension.   
     
     
         2 . The fan blade as set forth in  claim 1 , wherein said main body including both said cover and said end cap, the end cap at said leading edge, wherein there are a plurality of said step defined at each of said opposed ends of said cover on one of said suction wall and said pressure wall, and wherein said steps are defined at each of said opposed ends of said end cap on both said suction and pressure walls, and wherein all of said step dimensions are less than or equal to about 0.010 inch (0.0254 centimeter). 
     
     
         3 . The fan blade as set forth in  claim 2 , wherein an outer surface of said fan blade having a surface roughness and said surface roughness having a root means square value of less than about 60×10 −6  inch on at least a portion of a radial length of the main body. 
     
     
         4 . The fan blade as set forth in  claim 2 , wherein a filler material is provided between each of said opposed ends of said end caps and cover and said main body, with said filler material reducing the size of said steps, and said filler material being part of said cover and said end cap for purposes of measuring said dimensions of said steps. 
     
     
         5 . The fan blade as set forth in  claim 1 , wherein an outer surface of said fan blade having a surface roughness and said surface roughness having a root means square value of less than about 60×10 −6  inch on at least a portion of a radial length of the main body. 
     
     
         6 . The fan blade as set forth in  claim 1 , wherein a filler material is provided between at least one of said ends of said one of the end cap and the cover and said main body, with said filler material reducing the size of said step, and said filler material being part of said cover and said end cap for purposes of measuring said dimensions of said steps. 
     
     
         7 . The fan blade as set forth in  claim 1 , wherein said fan blade having a chord length, and a ratio of said step dimension to said chord length being less than or equal to about 0.001. 
     
     
         8 . The fan blade as set forth in  claim 1 , wherein said step occurring over at least from 20% of a blade span, measured from a platform to a radially outer tip of said airfoil. 
     
     
         9 . The fan blade as set forth in  claim 1 , wherein said fan blade is designed to rotate with a fan tip corrected speed below 1225 ft/second (368 meters/second) at bucket cruise. 
     
     
         10 . The fan blade as set forth in  claim 1 , comprising a shroud for connecting the fan blade to an adjacent fan blade. 
     
     
         11 . The fan blade as set forth in  claim 1 , wherein at least one of the main body, cover, and cap is formed of aluminum or an aluminum alloy. 
     
     
         12 . The fan blade as set forth in  claim 1 , wherein at least one of the main body, cover, and cap is formed of titanium or a titanium alloy. 
     
     
         13 . The fan blade as set forth in  claim 1 , wherein at least one of the main body, cover, and cap is formed of composite. 
     
     
         14 . The fan blade as set forth in  claim 1 , wherein at least one of the main body is formed of composite, a metal, or an alloy, and wherein the cover or the cap is formed of titanium or a titanium alloy. 
     
     
         15 . A gas turbine engine comprising:
 a fan drive turbine driving a fan rotor having a plurality of blades through a gear reduction;   each of said plurality of blades including a main body having an airfoil extending between a leading edge, and a trailing edge and each of said plurality of blades having a chord length, and each of said plurality of blades having at least one of:   (a) a channel closed by a cover, and   (b) an end cap covering at least one of the leading and trailing edges; and   the at least one of the cover and the end cap having a pair of opposed ends, and a step defined by at least one of a suction wall and a pressure wall of the airfoil, to an outer surface of said one of the cover and the end cap at one of said opposed ends, and a ratio of said step dimension to said chord length being less than or equal to about 0.001.   
     
     
         16 . The gas turbine engine as set forth in  claim 15 , wherein said main body including both said cover and said end cap, the end cap at said leading edge, wherein there are a plurality of said step defined at each of said opposed ends of said cover on one of said suction wall and said pressure wall, and wherein said steps are defined at each of said opposed ends of said end cap on both said suction and pressure walls, and wherein all of said step dimensions having said ratio being less than or equal to about 0.001. 
     
     
         17 . The gas turbine engine as set forth in  claim 16 , wherein a filler material is provided between each of said opposed ends of said end caps and cover and said main body, with said filler material reducing the size of said step dimensions, and said filler material being part of said cover and said end cap. 
     
     
         18 . The gas turbine engine as set forth in  claim 15 , wherein an outer surface of said fan blade having a surface roughness and said surface roughness having a root means square value of less than about 60×10 −6  inch on at least a portion of a radial length of the main body. 
     
     
         19 . The gas turbine engine as set forth in  claim 15 , wherein a filler material is provided between at least one of said ends of said one of the end cap and the cover and said main body, with said filler material reducing the size of said step dimensions, and said filler material being part of said one of said cover and said end cap. 
     
     
         20 . The gas turbine engine as set forth in  claim 15 , wherein said step occurring over at least from 20% of a blade span, measured from the platform to a radially outer tip of said airfoil. 
     
     
         21 . The gas turbine engine as set forth in  claim 15 , wherein said fan blade is designed to rotate with a fan tip corrected speed below 1225 ft/second (368 meters/second) at bucket cruise. 
     
     
         22 . The gas turbine engine as set forth in  claim 15 , comprising a shroud connecting adjacent ones of said blades. 
     
     
         23 . A method of manufacturing a fan blade comprising the steps of:
 providing a main body extending between a leading edge and a trailing edge, and having a suction wall and a pressure wall, with said main body having at least one of a channel enclosed by a cover, and an end cap covering at least one of said leading and trailing edges, with said at least one of the cover and the end cap being assembled to said main body, and defining a step by at least one of the suction and pressure walls and an end of the at least one of the cover and the end cap, and the step being made to be less than or equal to about 0.010 inch (0.0254 centimeter) in dimension.   
     
     
         24 . The method as set forth in  claim 23 , wherein the size of the step is reduced by adding a filler material which is considered part of the at least one of the end cap and the cover for purposes of measuring said step dimension. 
     
     
         25 . The method as set forth in  claim 23 , wherein the main body includes both the cover and the end cap and there are at least four of said steps associated with ends of the cover having one spaced toward the leading edge and one spaced towards the trailing edges and ends of the end cap on each of the pressure and suction walls, and all of said dimensions of said steps being made to be less than or equal to about 0.010 inch (0.0254 centimeter). 
     
     
         26 . The method as set forth in  claim 23 , wherein a surface roughness of an outer surface of the main body, and the at least one of the cover and the end cap is made to be less than about 60×10 −6  inch over at least a portion of a radial length of the main body. 
     
     
         27 . The method as set forth in  claim 23 , wherein a machining step is utilized to reduce the surface roughness. 
     
     
         28 . The method as set forth in  claim 23 , wherein the fan blade defining a chord length, and a ratio of said step dimension to said chord length being less than or equal to about 0.001. 
     
     
         29 . A method of designing a fan blade comprising:
 providing a main body having an airfoil extending between a leading edge and a trailing edge, and the fan blade having a chord length, the airfoil extending radially outwardly from a platform, and the fan blade having at least one of:   (a) a channel closed by a cover; and   (b) an end cap covering at least one of the leading and trailing edges; and   the at least one of the cover and the end cap having a pair of opposed ends, and a step defined by at least one of a suction wall and a pressure wall of the airfoil to an outer surface of said one of the cover and the end cap at one of said opposed ends, and a ratio of said step dimension to said chord length being less than or equal to about 0.001.   
     
     
         30 . The method as set forth in  claim 29 , wherein an outer surface of said fan blade having a surface roughness and said surface roughness having a root means square value of less than about 60×10 −6  inch on at least a portion of a radial length of the main body.