Blade fixing for a blade in a gas turbine engine

Abstract

The blade fixing comprises a firtree having a width between two opposite surfaces, each defining a plurality of successive necks separated from one another by arcuate lobes. Each of the opposite surfaces is substantially flat and substantially parallel to the other at the narrowest point of a first one of the necks that is closest to the platform.

1 . A blade fixing for a rotor blade in a gas turbine engine, the blade having a platform with the blade fixing projecting therefrom, the blade fixing comprising a firtree having a width between two opposite surfaces, each surface defining a plurality of successive necks separated from one another by arcuate lobes, the firtree having a local minimum width at a narrowest portion of each of said necks and a local maximum width at an apex of each of said lobes, each of the opposite surfaces being substantially flat and substantially parallel to the other at the narrowest portion of a first one of the necks that is closest to the platform. 
   
   
       2 . The blade fixing as defined in  claim 1 , wherein the remainder of the plurality of successive necks have an arcuate profile at the narrowest portion of the such necks. 
   
   
       3 . The blade fixing as defined in  claim 1 , wherein each of the surfaces have a radius of curvature at the narrowest portion of the first neck which is larger than a radius of curvature on either side of the narrowest portion of the first neck. 
   
   
       4 . The blade fixing as defined in  claim 1 , wherein the narrowest portion of each of the first necks has a radius of curvature which is larger than a radius of curvature at the narrowest portion of any other neck of the plurality. 
   
   
       5 . The blade fixing as defined in  claim 1 , wherein the opposite side surfaces are substantially symmetrical with reference to a medial plane of the blade fixing. 
   
   
       6 . The blade fixing as defined in  claim 1 , wherein the lobes decrease in width as a function of a distance between the lobes and the platform. 
   
   
       7 . The blade fixing as defined in  claim 1 , wherein opposite portions on the surfaces immediately adjacent to the platform are part of the first necks. 
   
   
       8 . A firtree for a blade in a gas turbine engine, the firtree generally projecting from a platform of the blade, the firtree comprising at least two pairs of opposite arcuate lobes, each lobe of a pair being on a corresponding side, the lobes generally decreasing in size between successive lobes starting from a first of the lobes with reference to the platform, the platform and the first lobe being separated on each of the opposite sides by a neck having a substantially flat section extending parallel to a medial plane of the firtree, the necks uninterruptedly blending to adjacent lobes. 
   
   
       9 . The firtree as defined in  claim 8 , wherein the firtree is substantially symmetrical with reference to the medial plane. 
   
   
       10 . A fixing for an airfoil blade for a gas turbine engine, the fixing comprising a firtree projecting radially from a platform of the airfoil blade and having a plurality of pairs of opposed lobes, the platform and lobes being areas of maximum fixing width separated by corresponding necks, the necks being areas of minimum fixing width, one of the necks closest to the platform having a radial height which is larger than a radial height of the other necks. 
   
   
       11 . The fixing as defined in  claim 10 , wherein the sides of the firtree have profiles that are substantially symmetrical with reference to the medial plane. 
   
   
       12 . The fixing as defined in  claim 11 , wherein the lobes decrease in size as a function of the distance of the lobes from the platform.