Blades
Percussive impacts due to bird strikes upon the hollow fan blades 20 are a well known problem. These percussive impacts not only deform previous fan blades but also reduce their stiffness. In accordance with the present invention, hollow fan blades 20 incorporate a cavity 23 within which, a matrix 24 with embedded expandable elements 25 , is located. Thus, upon a percussive impact these expandable elements 25 are released in order to create an internal pressure within the cavity 25 which acts outwardly in order to relieve deformation and also stiffen the blade 20 as a result of the over pressure within the cavity 23.
1. A blade for a gas turbine engine, the blade having a hollow cavity, the hollow cavity incorporating releasable bias means to present outward pressure when subjected to significant percussive load, wherein the releasable bias means comprising a matrix incorporating rupturable elements which rupture in use upon percussive load to provide the outward pressure wherein said rupturable elements are reactive and wherein said reactive rupturable elements release upon rupture reactants in order to react with other reactants from other reactive rupturable elements in order to provide the outward pressure.
2. A blade as claimed in claim 1 wherein the rupturable elements incorporate or generate a foam in order to provide the outward pressure.
3. A blade as claimed in claim 1 , wherein the rupturable elements release an adhesive and a foaming agent.
4. A blade as claimed in claim 3 wherein the adhesive is selected from the group comprising an epoxy, polyurethane and silicon.
5. A blade for a gas turbine engine, the blade having a hollow cavity, the hollow cavity incorporating releasable bias means to present outward pressure when subjected to significant percussive load, wherein the releasable bias means comprises a matrix incorporating rupturable elements which rupture in use upon percussive load to provide outward pressure, these rupturable elements are reactive, wherein the reactive rupturable elements release upon rupture two reactants in order to react in order to provide outward pressure.
6. A blade as claimed in claim 5 wherein the reactants are held within separate compartments of the rupturable elements.
7. A blade as claimed in claim 5 wherein a first reactant is held within the rupturable elements and a second reactant is held in breakable pills within the first reactant.
8. A blade as claimed in claim 5 wherein the rupturable elements incorporate or generate a foam in order to provide the outward pressure.
9. A blade as claimed in claim 5 , wherein the rupturable elements release an adhesive and a foaming agent.
10. A blade as claimed in claim 9 wherein the adhesive is selected from the group comprising an epoxy, polyurethane and silicon.
11. A blade for a gas turbine engine, the blade having a hollow cavity, the hollow cavity incorporating releasable bias means to present outward pressure when subjected to significant percussive load, wherein the releasable bias means comprises a matrix incorporating rupturable elements which rupture in use upon percussive load to provide outward pressure, the reactive rupturable elements contain reactants, wherein the reactive rupturable elements release upon rupture reactants in order to generate a foam in order to provide the outward pressure.
12. A blade as claimed in claim 11 , wherein the rupturable elements release an adhesive and a foaming agent.
13. A blade as claimed in claim 12 wherein the adhesive is selected from the group comprising an epoxy, polyurethane and silicon.
14. A blade for a gas turbine engine, the blade having a hollow cavity, the hollow cavity incorporating releasable bias means to present outward pressure when subjected to significant percussive load, wherein the releasable bias means comprises a matrix incorporating rupturable elements which rupture in use upon percussive load to provide outward pressure, the reactive rupturable elements contain reactants, wherein the reactive rupturable elements release upon rupture reactants in order to react in order to provide the outward pressure.
15. A blade as claimed in claim 14 wherein the matrix is selected from the group comprising elastomeric material, a foam, a viscous liquid and a resin.
16. A blade as claimed in claim 14 wherein the matrix is a vibration damping medium for the blade.
17. A blade as claimed in claim 14 wherein the rupturable elements incorporate points of weakness to facilitate rupture upon application of a percussive load.
18. A blade as claimed in claim 14 wherein the rupturable elements provide a directional response upon rupture with regard to the outward pressure.
19. A blade as claimed in claim 14 wherein the rupturable elements incorporate perforations to rupture by discharge through the perforations in the surface of the rupturable element.
20. A blade as claimed in claim 14 wherein the rupturable elements are differentially distributed and/or sized and/or variously responsive at different locations within the hollow cavity.
21. A blade as claimed in claim 14 wherein the blade incorporates means for blade venting to limit the extent of outward pressure presented within the hollow cavity.
22. A blade as claimed in claim 21 wherein the means for blade venting is at a tip of the blade.
23. A blade as claimed in claim 21 wherein the means for blade venting comprises perforation pimple release of a part of the blade surface.
24. A blade as claimed in claim 21 wherein the means for blade venting provides an indicator means for indication of percussive loads to the blade.
25. A blade as claimed in claim 24 wherein the indicator means comprises a sight hole for viewing blade venting in which presence of releasable bias means indicates percussive loading of a blade.
26. A blade as claimed in claim 24 wherein the indicator means comprises pop out sections which extend from the cavity to the surface of the blade and the pop out sections are displaceable so that they are raised above the surface of the blade upon rupture of the rupturable elements.
27. A blade as claimed in claim 14 wherein the rupturable elements incorporate or generate a foam in order to provide the outward pressure.
28. A blade as claimed in claim 14 , wherein the rupturable elements release an adhesive and a foaming agent.
29. A blade as claimed in claim 28 wherein the adhesive is selected from the group comprising an epoxy, polyurethane and silicon.
30. A blade as claimed in claim 14 wherein the releasable bias means changes colour when subjected to percussive load to provide indication means upon application of that percussive load in use.
31. A blade as claimed in claim 14 wherein the blade is a fan blade.
32. A gas turbine engine incorporating a fan blade as claimed in claim 14 .
33. A blade for a gas turbine engine, the blade having a hollow cavity, the hollow cavity incorporating releasable bias means to present outward pressure when subjected to significant percussive load, wherein the releasable bias means comprises a matrix incorporating rupturable elements which rupture in use upon percussive load to provide outward pressure, these rupturable elements are reactive, wherein the reactive rupturable elements release upon rupture reactants in order to react with said matrix in order to provide the outward pressure.
34. A blade as claimed in claim 33 wherein the rupturable elements incorporate or generate a foam in order to provide the outward pressure.