Sunday, March 15, 2009

Plastic in the hot section

According to Aviation Week, General Electric and Rolls Royce are going to make the third stage low pressure turbine vanes from a composite material on the F135 engine for the F35 Joint Strike Fighter.
Revolutionary. The hot section of jet engines runs so hot that up til now only exotic nickel super alloys could take the heat. The improvements in engine specific fuel consumption since the 1940's all come from better alloys that allow engines to run hotter with out melting the turbine. Now we have a composite that can take the heat.
Composites started with fiberglass (still used to make boats and Corvettes) and moved up to carbon fiber composites used for the fuselage of the newest Boeing 787 airliner (so new it hasn't made it's maiden flight yet). Composites offer far greater strength to weight ratios than metals. This composite is made from silicon carbide fibers with a ceramic binder. The final trick appears to be infiltrating the material with molten silicon to fill any voids. The high temperature composite can reduce the weight engines (the weightiest part of aircraft) giving better fuel consumption and longer range.
Hot section service is the most demanding application. A composite tough enough for the hot section is tough enough for plenty more applications.

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