Blade

Abstract

A blade having a root portion and an aerofoil portion, wherein the aerofoil portion has a tip remote from the root portion, and a leading edge and a trailing edge, and wherein the tip of the aerofoil portion has a set-back portion extending from the leading edge or the trailing edge of the aerofoil portion part way towards the respective other edge and set back from the remainder of the tip of the aerofoil portion towards the root portion.

1 . A blade comprising a root portion and an aerofoil portion, wherein the aerofoil portion has a tip remote from the root portion, and a leading and a trailing edge, and wherein the tip of the aerofoil portion has a set-back portion extending from the leading edge or the trailing edge of the aerofoil portion part way towards the respective other edge and set back from the remainder of the tip of the aerofoil portion towards the root portion. 
     
     
         2 . A blade as claimed in  claim 1 , wherein the set-back portion in the tip is serrated. 
     
     
         3 . A blade as claimed in  claim 2 , wherein the serrated set-back portion has shaped serration slots which extend not aligned with the circumferential direction of motion of the tip when the blade is rotating in use in a fan. 
     
     
         4 . A blade as claimed in  claim 3 , wherein the serration slots are approximately perpendicular to the surface of the tip which is flow-washed when the blade is rotating in use in a fan. 
     
     
         5 . A blade as claimed in  claim 3 , wherein the serration slots are 2 mm deep. 
     
     
         6 . A fan having a plurality of blades as claimed in  claim 1  and a fan casing around the tips of the blades, wherein as a result of the set-back portions in the tips the tip clearance area between tips and fan casing is changed by at least 1% of fan area as compared with a case in which the set-back portions in the tips were omitted. 
     
     
         7 . (canceled) 
     
     
         8 . A blade as claimed in  claim 4 , wherein the serration slots are 2 mm deep. 
     
     
         9 . A fan having a plurality of blades as claimed in  claim 2  and a fan casing around the tips of the blades, wherein as a result of the set-back portions in the tips the tip clearance area between tips and fan casing is changed by at least 1% of fan area as compared with a case in which the set-back portions in the tips were omitted. 
     
     
         10 . A fan having a plurality of blades as claimed in  claim 3  and a fan casing around the tips of the blades, wherein as a result of the set-back portions in the tips the tip clearance area between tips and fan casing is changed by at least 1% of fan area as compared with a case in which the set-back portions in the tips were omitted. 
     
     
         11 . A fan having a plurality of blades as claimed in  claim 4  and a fan casing around the tips of the blades, wherein as a result of the set-back portions in the tips the tip clearance area between tips and fan casing is changed by at least 1% of fan area as compared with a case in which the set-back portions in the tips were omitted. 
     
     
         12 . A fan having a plurality of blades as claimed in  claim 5  and a fan casing around the tips of the blades, wherein as a result of the set-back portions in the tips the tip clearance area between tips and fan casing is changed by at least 1% of fan area as compared with a case in which the set-back portions in the tips were omitted. 
     
     
         13 . A fan having a plurality of blades as claimed in  claim 8  and a fan casing around the tips of the blades, wherein as a result of the set-back portions in the tips the tip clearance area between tips and fan casing is changed by at least 1% of fan area as compared with a case in which the set-back portions in the tips were omitted.