Graham Warwick/ATLANTA
DOW-UNITED Technologies Composite Products (Dow-UT) has completed the first turbofan fan exit case to be built from composites. The 2.8m-diameter case has been produced under a $14.8 million contract from the US Advanced Research Projects Agency, using an advanced resin-transfer moulding (RTM) process developed by Dow-UT.
Company president Tom Scarpati says that the fan exit case could not have been produced using conventional "pre-preg" composites. "We have demonstrated, with RTM, not only that we can make parts cost-effectively, but in a scale which has surprised many. This opens up areas in engine and aircraft structures which were not previously viable candidates for composites," he says.
In the RTM process, dry composite plies are placed in a mould to produce a preform with the net shape of the final part. Resin is then injected into the mould.
Scarpati says that Wallingford, Connecticut-based Dow-UT is achieving "extraordinary" repeatability and "incredible" laminate quality with RTM. "The belief that RTM is nothing more than a laboratory process is absolutely and unequivocally false," he maintains.
"Over the past two years we have put in place a production capability," Scarpati says. The Dow Chemical/United Technologies joint venture is producing some 150 different RTM parts for the Lockheed Martin/ Boeing F-22, including wing sine-wave spars, plus engine-inlet screens for the Lockheed Martin F-117, and fan spacers and thrust-reverser cascades for Pratt & Whitney's PW4000-series turbofans.
The fan exit case for P&W's future Advanced Ducted Prop high-bypass turbofan is significant because of its size and complexity. Conventional cases are fabricated from titanium or aluminium. An RTM case would be 20-35% lighter than its metal equivalent and competitive on cost, something which could not be achieved using conventional composites, Scarpati says.
The RTM case will be tested under representative birdstrike and blade-off loads and Dow-UT is proposing building a unit to allow testing in an existing engine. Dow-UT is already talking to General Electric and P&W about using RTM in other areas. "The process clearly has application to fan blades," Scarpati says.
Source: Flight International
