The Little Engine That Couldn't | Flight Today | Air & Space Magazine
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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IT'S AUGUST 26, 2002, A CLEAR, HOT MORNING at Albuquerque International Sunport. Poised for takeoff on Runway 17 is a small orange and white twin-engine jet carrying a heavy load of hype and hope. A press release from its manufacturer says the first flight of this prototype will do nothing less than “forever change the landscape of transportation.” The Eclipse 500’s promised $837,500 price tag—an astonishingly low figure, barely a quarter that of the next cheapest jet—and 56-cents-a-mile direct operating cost have brought in deposits for more than 2,000 airplanes, potentially making it the best-selling private jet in history even before it flies.

Two engine nacelles, stovepipe-skinny and barely four feet long, sprout from the rear fuselage. They hold the key to the Eclipse’s remarkable price and performance claims: a pair of Williams International EJ22 fanjets, breakthrough powerplants developed by Sam Williams, the renowned guru of small jet engines. Using what Eclipse calls “disruptive” technology, the EJ22 has churned out 770 pounds of thrust in ground tests, yet, at 85 pounds, you could pick it up. This 9:1 thrust-to-weight ratio is unprecedented, almost double that of any commercial jet engine. It’s the breakthrough that can make the Eclipse 500 a landscape changer.

Albuquerque Tower clears N500EA for takeoff, and test pilot Bill Bubb releases the brakes and shoves the twin thrust levers forward. The EJ22s spool up into a soft whoosh and the airplane begins to accelerate down the runway.

But something’s wrong. The acceleration is lethargic, especially for an airplane loaded so lightly. In the hot, thin, mile-high air, the EJ22s can generate barely half their rated thrust. After a leisurely takeoff roll of more than 3,000 feet, the airplane lifts off and begins a gentle climb, paralleling the Sangre de Cristo mountains off its left wing. For about an hour, Bubb flies the planned test routine, checking out general handling qualities and systems operation. Overall, the flight is free of major glitches.

And yet, as the little jet taxies back toward the cheering employees at the Eclipse hangar, it’s already clear that the new EJ22 engines aren’t going to hack it.

The Eclipse 500 never again flew with EJ22s. Three months later, Eclipse Aviation announced: “The EJ22 is not a viable solution for the Eclipse 500 aircraft, and Williams International has not met its contractual obligations.” Williams conceded that it had run into “a number of challenges” with the EJ22 but insisted it had satisfied the contract, implying that the airplane had simply grown too heavy.

Eclipse hurriedly signed a deal with Pratt & Whitney to develop a smaller version of a more conventional engine. The PW610F would develop 900 pounds of thrust, but it would weigh 260 pounds—triple the weight of the EJ22. The extra power would give the Eclipse 500 a bit better speed and climb, but there was a big downside: an empty-weight gain of 700 pounds and a 20 percent increase in fuel consumption. The remarkable price and cost projections eventually ballooned to $1.3 million and 89 cents a mile. Three years later, flight tests of the P&W-powered Eclipse 500 are proceeding smoothly, but it’s still not clear whether it will change the landscape of transportation.

The failure of the Williams EJ22 to achieve Federal Aviation Administration certification in the Eclipse and the engine’s disappearance from public view were bitter disappointments to those who for decades have yearned for a certified engine that could lead to a new generation of small, affordable jets. The failure was also a blow to the reputation of its creator, Sam Williams, now 84, who essentially invented the small turbofan engine in the 1960s and remained its unchallenged mastermind for more than three decades.

Williams wasn’t the first to build a tiny jet engine. Back in the early 1950s, the French-built Turboméca Palas, with 330 pounds of thrust, inspired the creation of half a dozen oddball experimental Euro mini-jets. The Palas grew into the Marboré series (660 to 1,058 pounds of thrust), which powered a number of small military jets, such as the Morane-Saulnier 760 Paris four-seater and Cessna T-37 trainer. (The latter used the J-69, a version of the Marboré made by the U.S. company Teledyne CAE.) In the 1970s, the French firm Microturbo lowered the bar with the 220-pound-thrust TRS 18, which flew in the Italian Caproni A21J sailplane and in U.S. designer Jim Bede’s BD-5J airshow jet. Only 24 inches long, the TRS 18 is still the smallest jet engine ever to power a manned aircraft.

Those early mini-engines had a problem, though. Like all turbojets, they sucked up prodigious amounts of fuel. Worse, small aircraft are penalized by the pitiless exponential mathematics of scaling down: Reduce an airplane’s length by half, and internal volume for fuel shrinks eightfold. The BD-5J had an endurance of about an hour or so and a range of around 300 miles.

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