The alternate engine that General Electric is developing for use on the F-35 joint strike fighter has run into problems. After nine months of “system development and demonstration” testing, it has only managed to run for 52 hours and had four failures. At the same stage in development, the competing Pratt & Whitney engine had undergone 700 hours of SDD testing with no failures.
The repeated failure of the GE engine has given rise to rumors that its combustor — the vital component that burns a mixture of fuel and compressed air — will have to be redesigned. One version of the rumor has GE giving up all its testing time at the Air Force’s Arnold Engineering Development Center until next April — the kind of lengthy delay typically associated with a design problem. If true, this would put the GE team in a financial bind, because it has already expended 70% of funding for the current phase of development.
A recent “joint estimating team” finding of potential cost overruns in development of the F-35 fighter traced 28% of projected cost problems to the alternate engine. While the estimating team is probably being too pessimistic about the fighter, the prediction of a big funding shortfall on the alternate engine appears to reflect the difficulties the GE engine has encountered. A normal failure rate in development of a new gas turbine engine would be on the order of one incident every 300 hours, but GE seems to be having problems every 13 hours. As a result, it may be up to a year behind schedule on its testing plan.
This issue underscores a logical flaw in the case for an alternate engine. Backers argue that having a second engine is insurance against a design flaw in the primary powerplant being built by Pratt & Whitney for the single-engine F-35 fighter. But that reasoning works both ways — add a second engine to the mix, and you’ve doubled the potential for design issues, just like you’ve doubled the cost of developing engines by having to fund two design teams and two development programs. With several billion dollars remaining to be spent before the alternate engine joins the fleet, there is still time to rethink whether a second engine is really needed. The Pentagon says one engine is enough.
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