Posted on 06/09/2006 1:47:00 PM PDT by Paul Ross
GE's Alternative Engine Program Also Facing Hiccups During Development
By David A. Fulghum
06/02/2006
Developing an engine with all the necessary power and flexibility to both fly supersonic and then land - vertically - a stealthy, bomb-carrying fighter is proving to be a tough proposition for all the engine companies involved.
Officials at General Electric, developer of the F-35 Joint Strike Fighter's alternate engine program, confirmed that they've had problems with a prototype engine that was designed in conjunction with partner Rolls-Royce. Its role is to test advanced parts destined for use in a more mature System Development and Demonstration version of the future F136 engine. This closely follows revelations by Pratt & Whitney program officials that the Short Take Off and Vertical Landing of their F135, the primary engine for JSF, has overheating problems.
GE officials say that when testing prototype engine 03 (of three built for pre-SDD research) in April, an oil leak from a pump just in front of the high-pressure compressor stage caused an engine imbalance. The imbalance, in turn, triggered a compressor stall. Such events are usually accompanied by a loud explosion and a jet of fire issuing from the front of the engine as airflow through the engine stagnates and then reverses.
The mishap - during which the compressor blades rubbed against the case of the engine - produced damage to the tips of a number of new, low-pressure turbine blades being developed for inclusion in the SDD F136 engine. The prototype, designed to demonstrate the general concepts of the F136 engine, also was testing new hardware in its combustor, which was not affected.
"It was not completely trashed," says a company official. The repaired 03 engine will resume testing with the first SDD-ready LPT blades and combustor upgrades later this year. The prototype engine 02 will test an array of the first, SDD-development engine hardware - destined for the F136 - in early 2007. The 01 prototype is only a core and is no longer being used in the program.
"We ran those to get the [alternate engine] contract," he says. "Now, the next couple of years we're going to put SDD components in them to mature and evaluate those [newer technologies]."
Not a requirement
The test that resulted in the compressor stall was not a requirement for the F136 development program. "This was our own decision [to run the test], because we had the hardware available and we wanted to build some data on it," says a GE official. In fact, they say there was no testing schedule for this year at all. But company planners wanted to continue risk-reduction efforts on their own. A test cycle that began in February was designed to gather data on engine control software. It also involved 33 hours of engine runs up to maximum power. The oil leak developed in front of the high-pressure compressor. The JSF Joint Program Office is reviewing an analysis of the compressor stall.
GE officials say the April incident does not impact the F136 development schedule or cost projections. The P&W F135 has already demonstrated its specified thrust of 40,550 pounds. The GE/Rolls-Royce team will start assembling its first SDD F136 engines in 2007-2008 and have them running by late 2008. The plan has been to let the F136, which was started later than the F135 program, incorporate additional technological advances.
"So we've got an opportunity to size the engine closer to the requirements of the aircraft," a GE official says. "That's one of the advantages of being a program behind Pratt. They had to freeze their design. We don't have to freeze the design until 2007. But the technical advantage is that as the aircraft evolves, we're closer to the actual requirement because we're coming down the pipe a little later."
Critical element
One critical element will be the size of the combustor where fuel and air are mixed and ignited. A larger combustor could result in greater thrust. Both companies are looking for engine components that are made of lightweight material, withstand higher core temperatures and offer increased thrust.
William J. Gostic, vice president of F135 programs for Pratt & Whitney, expressed the challenge faced by both engine teams.
"It's not unusual to pull these qualification engines during the tests because of the abusive nature of some of the testing we're doing," he says. The discipline and requirement is that "if you find things in the test program, they are things that you want to understand as early as possible. If you chose to ignore them, they tend to haunt you for years if not decades. We've learned to be aggressive and to go understand what we see in these engines."
Raise your hand, test pilots, if you don't mind hovering on THAT engine. Did they scope it? Every blade? Every stage?
And you thought you had a bad job.
BUMP!
BUMP!
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