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The technology behind VLJs
VLJ technology centers on a new generation of engines and avionics that can give little jets very big jet capability and good fuel economy at reduced weights. At 400 mph at 41,000 feet, a typical twin-engine VLJ burns less than 100 gallons per hour. Fully loaded, all of these airplanes weigh less, sometimes a lot less, than 10,000 pounds. The features now available on VLJs such as the Citation Mustang include 3D synthetic vision-something that gives pilots a view of terrain and runways in any weather. In the cockpit, you can dial up real-time weather from anywhere in the country on the computer screen. Passengers can listen to XM satellite radio. This is technology not found on airliners or even most business jets.
The engines are a new generation of lightweight turbofans that were offshoots of NASA research and lessons learned while building cruise missile engines during the 1960s and 1970s. About the time Cessna was introducing its first Citation, the 500, in 1972, Dr. Sam Williams, founder of engine-maker Williams International, was thinking about little engines for little jets. "He always thought anyone who could fly would prefer a jet," said Matt Huff, vice president of business development for Williams.
His first foray into the market was what would become the 2,300-pound-thrust FJ-44 turbofan. Williams designed it initially to compete as the powerplant on the Pentagon's JPATS training aircraft. It lost that contest, but was chosen to power the Sino Swearingen SJ30, the Beechcraft Premier I and the Cessna Citation CJ, an airplane that was lighter and faster than the original Citation 500. The engine entered service in 1993 and Williams already has produced 2,500 of them.
A downscaled version of the FJ-44, the FJ-33, would later be selected to power VLJs, including those from Adam, ATG, Cirrus, Diamond and Piper. The FJ-33 weighs just 300 pounds and delivers 1,000 to 1,500 pounds of thrust. It incorporates advances pioneered on the FJ-44, such as scalloped exhaust pipes that reduce engine noise and improve fuel efficiency. The fan stage features blades that are widely swept and rounded, which further contributes to lower noise and better economy. Williams pioneered the use of a single-piece, single-forged titanium fan blade and fan disk assembly called a "blisk" that reduces weight and the need for maintenance and is more damage tolerant than the conventional separate disk-blade-spacer designs.
But as early as the 1980s, Sam Williams was thinking smaller. He agreed to provide engines to one of the earlier failed attempts at VLJs, the FoxJet, and by 1996 Williams partnered with NASA to produce a 700-pound-thrust turbofan for light, four- to six-passenger aircraft. He hired aircraft designer Burt Rutan to build a futuristic aircraft, the V-JETII, to showcase an early version of the engines. Rutan, who is the closest thing the small-airplane community has to a rock star, would later proclaim, "Propeller airplanes are dead." The V-JET arrived at AirVenture Oshkosh [Wis.], the world's largest airshow, in 1997. Vern Raburn, an avid pilot and former computer executive, noticed it right away.
A year later, Raburn founded Eclipse, a company whose stated goal was to produce at least 500 twin-engine VLJs a year for $775,000 each (1998 dollars), using automotive-industry-style assembly lines and an advanced metal-bonding technique called "friction stir welding" that eliminated most of the riveting. The Eclipse was designed around the new Williams EJ-22 engines and the Avidyne Avio integrated computer screen avionics suite. The problem was that neither worked well enough on the aircraft as designed, forcing Eclipse to find other suppliers and redesign a good deal of the airplane, thus causing delays. And more delays. Eclipse eventually turned to Pratt & Whitney Canada for its 600 series engines, the same new generation of powerplant as on the Cessna Citation Mustang and Embraer Phenom 100, and a combination of companies to finish the avionics.
Meanwhile, one company, Spectrum Aeronautical, thinks more radical technology may be required. The firm, which Austin Blue runs, toiled in secret until 2005, when it removed the wraps from its 10-seat Model 33 jet. The company claims the aircraft will have a range of 2,000 nautical miles and cruise at 477 mph with the same hourly fuel consumption as the much smaller Eclipse. It will also be able to use ridiculously short runways. On its maiden flight from Spanish Fork, Utah (elevation 4,529 feet), in January 2006, the Spectrum 33's reduced-power takeoff roll was just 750 feet, less than a third of what a Cessna Citation CJ2 would have required.
Spectrum uses a proprietary and automated method of fabricating carbon fiber that provides stiffness and support. The entire aircraft fuselage weighs just 300 pounds. With full fuel and passengers, the Spectrum will weigh approximately 7,300 pounds or about half as much as a comparably performing aluminum business jet. Spectrum is in the process of developing the Model 33 and a larger sibling, the S-40.