Shortened support for compressor variable vane

Abstract

A variable vane assembly comprises an upstream vane stage including an airfoil coupled with an upstream vane stem and an upstream vane arm, configured to drive the upstream vane stem to rotate. The upstream vane stem is supported in an upstream housing boss. A downstream vane stage includes an airfoil coupled with a downstream vane stem and a downstream vane arm, and configured to drive the downstream vane stem to rotate. The downstream vane stem is supported in a downstream housing boss. A first clearance is defined between a radially inner end of the upstream vane arm and a radially outer end of the upstream housing boss. A second clearance is defined between a radially inner end of the downstream vane arm and a radially outer end of the downstream housing boss. A clearance ratio of the second clearance to the first clearance is greater than or equal to 10.

1 . A variable vane assembly comprising:
 an upstream vane stage including an airfoil coupled with an upstream vane stem and an upstream vane arm and configured to drive said upstream vane stem to rotate, with said upstream vane stem supported in an upstream housing boss, and a downstream vane stage including an airfoil coupled with a downstream vane stem and a downstream vane arm and configured to drive said downstream vane stem to rotate, with said downstream vane stem supported in a downstream housing boss; and   a first clearance defined between a radially inner end of said upstream vane arm and a radially outer end of said upstream housing boss, and a second clearance defined between a radially inner end of said downstream vane arm and a radially outer end of said downstream housing boss, with a clearance ratio of said second clearance to said first clearance being greater than or equal to 10.   
     
     
         2 . The variable vane assembly as set forth in  claim 1 , wherein said clearance ratio is greater than 35. 
     
     
         3 . The variable vane assembly as set forth in  claim 1 , wherein a top hat bushing is inserted in said upstream housing boss, and said top hat bushing defining said radially outer end of said upstream housing boss. 
     
     
         4 . The variable vane assembly as set forth in  claim 1 , wherein a downstream bushing supports said downstream vane stem in said downstream housing boss, with said downstream bushing having an outer diameter and extending for a length, and an upstream bushing ratio of said length to said outer diameter being greater than or equal to 2.5 and less than or equal to 3.0. 
     
     
         5 . The variable vane assembly as set forth in  claim 4 , wherein said downstream vane stem has an outer periphery supported within said downstream bushing that has at least one greater diameter portion and a lesser diameter portion. 
     
     
         6 . The variable vane assembly as set forth in  claim 4 , wherein there are a pair of greater diameter portions on opposed sides of said lesser diameter portion. 
     
     
         7 . The variable vane assembly as set forth in  claim 4 , wherein said downstream bushing includes graphite. 
     
     
         8 . The variable vane assembly as set forth in  claim 7 , wherein said upstream vane stage having an upstream bushing positioned within a bore of said upstream housing boss, and said upstream bushing extending for a length and having an outer diameter and an upstream bushing ratio of said length to said outer diameter being greater than 3.0. 
     
     
         9 . The variable vane assembly as set forth in  claim 4 , wherein said upstream vane stage having an upstream bushing positioned within a bore of said upstream housing boss, and said upstream bushing extending for a length and having an outer diameter and an upstream bushing ratio of said length to said outer diameter being greater than 3.0. 
     
     
         10 . The variable vane assembly as set forth in  claim 9 , wherein said downstream bushing includes graphite. 
     
     
         11 . A compressor section comprising:
 a plurality of rotor blade stages;   a variable vane assembly including an upstream vane stage including an airfoil coupled with an upstream vane stem and an upstream vane arm configured to drive said upstream vane stem to rotate, with said upstream vane stem supported in an upstream housing boss, and a downstream vane stage including an airfoil coupled with a downstream vane stem and a downstream vane arm and configured to drive said downstream vane stem to rotate, with said downstream vane stem supported in a downstream housing boss; and   a first clearance defined between a radially inner end of said upstream vane arm and a radially outer end of said upstream housing boss, and a second clearance defined between a radially inner end of said downstream vane arm and a radially outer end of said downstream housing boss, with a ratio of said second clearance to said first clearance being greater than or equal to 10.   
     
     
         12 . The compressor section as set forth in  claim 11 , wherein said clearance ratio is greater than 35. 
     
     
         13 . The compressor section as set forth in  claim 11 , wherein a top hat bushing is inserted in said upstream housing boss, and said top hat bushing defining said radially outer end of said upstream housing boss. 
     
     
         14 . The compressor section as set forth in  claim 11 , wherein a downstream bushing supporting said downstream vane stem in said downstream housing boss, with said downstream bushing having an outer diameter and extending for a length, and an upstream bushing ratio of said length to said outer diameter being greater than or equal to 2.5 and less than or equal to 3.0. 
     
     
         15 . The compressor section as set forth in  claim 14 , wherein said downstream vane stem has an outer periphery supported within said downstream bushing that has at least one greater diameter portion and a lesser diameter portion. 
     
     
         16 . The compressor section as set forth in  claim 14 , wherein there are a pair of greater diameter portions on opposed sides of said lesser diameter portion. 
     
     
         17 . The compressor section as set forth in  claim 14 , wherein said downstream bushing includes graphite. 
     
     
         18 . The compressor section as set forth in  claim 17 , wherein said upstream vane stage having an upstream bushing positioned within a bore of said upstream housing boss, and said upstream bushing extending for a length and having an outer diameter and an upstream bushing ratio of said length to said outer diameter being greater than 3.0. 
     
     
         19 . The compressor section as set forth in  claim 14 , wherein said upstream vane stage having an upstream bushing positioned within a bore of said upstream housing boss, and said upstream bushing extending for a length and having an outer diameter and an upstream bushing ratio of said length to said outer diameter being greater than 3.0. 
     
     
         20 . The compressor section as set forth in  claim 19 , wherein said downstream bushing includes graphite.