Graham Warwick/WASHINGTON DC
Boeing says its X-32 Joint Strike Fighter (JSF) concept demonstrator remains relevant despite the company's decision to revise its design for the operational JSF. Programme general manager Frank Statkus says the delta-wing X-32s will still serve to reduce the risk attached to development of its JSF, now a more conventional swept-wing design.
Dennis Muilenburg, director, JSF weapon system, says Boeing revised its design to meet the latest joint interim requirements document (JIRD 3) produced by the USAir Force, Navy, Marine Corps and UK Royal Navy. The previous design, configuration 372, "...was still too heavy," he says.
With the revised design, configuration 373, "...we are in really good shape against JIRD 3," says Statkus. "In JSF programme office terminology, 373 is the 90% solution," says Muilenburg - a measure of how close the design is to the final JSF requirements.
The switch to a smaller swept wing and separate horizontal tail reduced weight, but was made primarily to increase pitch control and improve aircraft-carrier suitability. This was not possible with the original delta wing, Muilenburg says, without decreasing low-observability (LO) performance.
Other changes include redesign of the inlet lip from forward swept to aft swept. This reduced weight, improved high angle-of-attack performance and - "surprisingly," says Muilenburg - did not degrade LO performance. The twin canted vertical tails were reshaped, as was the canopy, to reduce weight. The fuselage, meanwhile, is "...more or less unchanged," he says.
The revised configuration "...is nothing more than a maturation of the design," says Statkus, adding: "This maturation of the configuration is the best-fit solution to the requirements as they are today, with the greatest opportunity for improvement in the future. We will continue to evolve the design until we get to the configuration we will propose for engineering and manufacturing development."
While the two X-32s under construction represent an outdated configuration, they are still relevant, Boeing says. "There was never a requirement to make the demonstrator aircraft identical to the PWSC [preferred weapon system concept] eventually evolved," says Statkus.
The three principal aims of the demonstrator programme, says Muilenburg, are to address commonality, carrier suitability and transition between vertical and forward flight. "We have demonstrated maximum commonality with the two aircraft, building them at the same time on the same machines," he says.
With carrier approach and landing, "...what we are really interested in is whether the aircraft flies as predicted," Muilenburg says. The conventional take-off and landing X-32A will be used to validate models used to develop control laws. "With the demonstrator, the toughest task will be getting it on the deck with that wing. Then we will extrapolate the data."
Transition is "in the bag", he says, because the propulsion and control system in the X-32B short take-off and vertical landing demonstrator "...is identical to 373," Muilenburg says. Windtunnel and ground-effect testing has shown that performance in forward and vertical flight is improved by the new configuration, he adds.
Source: Flight International
