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Cessna’s T-37 was dubbed “Tweety Bird” for its shrill Teledyne CAE J-69s. (USAF)

The Little Engine That Couldn't

The new Eclipse 500 lightjet will no doubt make a lot of customers happy

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(Continued from page 2)

John Adamczyk, the NASA senior technologist on the project, still remembers his shock upon first seeing the FJX-2’s parts laid out. “I just shook my head in amazement at how small it all was. It looked like someone was assembling a Swiss watch.” A five-stage compressor from the FJX-2 that Williams showed off at the 1997 Oshkosh, Wisconsin airshow looked more like the business end of a Cuisinart than the seeds of an aeronautical revolution. With each stage intricately carved from a single piece of titanium, it weighed one pound, three ounces. “You could hold it in the palm of your hand,” recalls Adamczyk, still awestruck.

But the doubts vanished a year or so into the program, after the first test of the main compressor. “All the numbers matched our analysis,” remembers Adamczyk. “It really gelled at that point.” The complete engine first ran in August 1999 and was soon hitting its predicted thrust numbers. Four engines eventually accumulated a total of almost 900 starts and more than 500 hours of running time in the test cell. Testifying before Congress in 2000, Sam Williams declared the FJX-2 a “major success.” Adamczyk, a 30-year veteran who has worked on numerous jet engine projects, calls the FJX-2 “one of the high points of my career.”

All the while, Williams had been promoting the concept of a very light jet (VLJ) that could eventually use his new engine. In 1996, he’d hired Burt Rutan to build a demonstrator aircraft, the four-seat V-Jet II. Williams’ contract with NASA called for the V-Jet II to fly with a pair of FJX-2s as the capstone to the GAP project. But it initially flew with FJX-1s, man-rated versions of the F107 cruise missile engine rated at 550 pounds of thrust. With Goldin in attendance, the V-Jet II created a sensation at Oshkosh in 1997 with the noisy, underpowered FJX-1s. Among the thousands of salivating airplane buffs in the audience was a wealthy pilot and businessman named Vern Raburn.

An early Microsoft executive and stockholder, Raburn had just left a job overseeing the technology investments of billionaire Microsoft co-founder Paul Allen, for whom he jetted around the country at the controls of a Williams-powered CitationJet. Raburn had the restless soul of an entrepreneur, and he had long nurtured the same vision as Williams: a small, inexpensive jet airplane. Galvanized by the V-Jet II and reports of the extraordinary little FJX-2, Raburn signed a deal with Williams in May 1998 to jointly develop a five- or six-seat VLJ. It would be powered by an FAA-certified version of the FJX-2, to be called the EJ22. Together, Sam Williams and Vern Raburn were going to revolutionize aviation.

With $60 million in investors’ money, a board of directors studded with high-tech corporate heavyweights, and an exclusive deal with Williams for the EJ22, Raburn launched Eclipse Aviation in March 2000. Williams, citing the Eclipse deal, persuaded NASA to skip the FJX-2 flights in the V-Jet II. This enabled Williams to get its final GAP payment sooner and turn immediately to the task of transforming its test-cell tour de force into a viable FAA-certified engine.

Exactly how did such a little engine achieve such extraordinary performance? Officially, nobody’s saying. The Williams company, privately held and with a long history of military projects, is secretive about technical details. NASA and Eclipse people who worked on the project, bound by confidentiality agreements imposed by Williams, are likewise mum.

“I think I can tell you that the main reason for the engine’s light weight is the architecture,” says NASA’s general aviation champion, Bruce Holmes, referring to the configuration of a jet engine’s fan, compressors, combustor, and turbines. “But I’d go to jail if I told you what that architecture was.”

Holmes can rest easy. I managed to ferret out the FJX-2’s architectural secret anyway: Instead of the usual two compressors, it had three, each spinning independently at its optimum rotation speed on one of three concentric shafts and driven by its own turbine. Designers call this unusual configuration a three-shaft, or three-spool, engine (see “Spools,” above).

The giveaway is on the instrument panel of the original Eclipse 500. Most jets have two readouts: N1 for the low-pressure (LP) compressor/fan, and N2 for the downstream high-pressure (HP) compressor. The Eclipse had an N3 gauge, which points to the presence of a third, intermediate-pressure (IP) compressor. Ed Lays, a retired Williams engineer not bound by any secrecy agreements, confirms that the FJX-2 was a three-shaft design.

A three-spool engine can be very efficient. “It gives you a lot of flexibility in matching compressors and turbines,” says Burkardt (“Not that I’m saying the FXJ-2 was or was not a three-spooler,” he adds dutifully). However, a three-shaft engine is mechanically complex, with “bearings and seals out the ying-yang,” in the words of Teledyne CAE veteran designer Gerry Merrill. Only two three-spool engines have ever been certified for commercial use: the Rolls-Royce RB.211 family of airliner engines first certified in the ’70s, and the Garrett ATF3, a fearsomely complex and troublesome bizjet engine that flopped in the marketplace 10 years later.

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