Problems with the design of the engine nacelle inlets have caused at least a three-month delay in the development of the Williams FJ44-2C-powered Spirit Wing Learjet 25D. “The difficulty is that the inlets must act as radiators, too,” explained Calvin Burgess, president and owner of Guthrie, Okla.-based Spirit Wing.
Because of the high temperature of the bleed air from the FJ44s, about 800 deg F compared with the 550 deg F of the Learjet’s original GE CJ610 engines, all the bleed air from the FJ44s must be routed through the stainless steel inlets to cool the air before it goes to the rest of the airplane. “Nordam conducted 11 trials with various inlet configurations,” Burgess said. “The last two, completed a few weeks ago, worked.” As soon as Spirit Wing receives the nacelles, the engines will be hung. “The pylons are on, the engines are ready to be mounted and the wiring is done,” said Burgess, anticipating that first flight of the conforming prototype would slip from September to sometime in the fall, probably October. Certification, earlier planned for the fourth quarter, has moved to next spring.
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