Too Fat To Fly?

Lockheed Martin engineers have pushed back the date by a year for the first flight of the F-35 Joint Strike Fighter, claiming that the plane has to skinny down first. Kathy Crawford, Public Affairs Officer for the JSF Fighter Program, confirmed that the first flight will not happen until 2006, primarily due to the weight issue. "They have added some extra time to look at the design and find some ways to cut weight out of the aircraft," she says. The design for the Navy and Air Force version is about 1,400 lbs (or approximately 5 percent) over weight, while the Marine Corps version is a blubbery 2,300 lbs (7 percent) over its weight target. Weight is extremely critical in both cases but in particular for the Marine Corps version, given that the design must achieve both supersonic flight and vertical lift. (For a detailed story on the trade-offs, see The Engineer of the Year story in the 02.23.04 issue of Design News, page 58, http://rbi.ims.ca/3848-537). Joking about forcing male pilots to fly in their underwear aside, Crawford says that engineers are working on various trade studies to see where they can trim the fat. "The engine is in good shape, so they're concentrating on areas within the airframe itself," she says. Specific areas targeted for so-called "spot reductions" are the cabling, routing hookups, and fasteners. Why is the weight so far off the target? One possible reason: It isn't an easy thing to estimate. Engineers perform what they call parametric weight studies early in the design cycle of a new aircraft, taking weight figures for similar parts and pieces from legacy airplanes to calculate a weight. Clearly, there weren't enough parametrics for such revolutionary airplanes, and at the detailed design stage a lot of the new systems came out heavier than anticipated.