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Aviation History
2002
2002 - 0143.PDF
Airborne warfare Northrop boom strength. "It's like putting on a very Grumman long nose," says Wlezien. "The challenge is sees QSP as in the energetics." leading to a Another active method of boom reduc- future long- tion being investigated is the thermal keel, range strike a linear ramjet which has the effect of aircraft virtually lengthening the aircraft and (above) spreading out the initial pressure rise, reducing boom loudness. "Airframers are looking at whether they can integrate the technology," says Wlezien. But such solutions may not be needed. "A key finding of our studies was that the QSP goals could be achieved without active or exotic boom reduction technologies, which are too immature," says Boccadoro. Making history Northrop Grumman hopes to prove air craft shaping is sufficient by flying the F-5 Sonic Boom Demonstrator (SBD). "We are on the verge of making aviation history," says Boccadoro. "We have never done a low-boom supersonic flight before." Low boom is not about reducing shock waves, he says, but about changing the sonic boom signature by shaping the air craft to stop shock-waves coalescing into a classic "N-wave". The F-5 SBD will have a reshaped forward-fuselage to modify pres sure distribution and produce a non- coalesced boom with a "flat-top" signature. "A flat-top signature is a substantial manipulation of the pressure wave." says Boccadoro. Lengthening and blunting the F-5's nose will strengthen the bow shock, while reshaping the lower fuselage will control the pressure rise behind the shock, managing the compression and expansion waves to prevent coalescence. While the goal of the test is to prove the pressure wave can be manipulated into a shape that persists to the ground, it will result in a quieter boom. "We expect the F-5 SBD to generate a flat-top wave with a substantial reduction in the magnitude of the initial overpressure as a result of shap ing," says Boccadoro. If the F-5 tests succeed, the next step could be a low-boom, efficient supersonic demonstrator, although nothing has been funded beyond QSP Phase 2. "The goals look reasonably attainable. In Phase 2, the contractors must make a compelling case the vehicle is doable," says Wlezien. • PART TWO FOLLOWS NEXT WEEK www.flightinternational.com FLIGHT INTERNATIONAL 15-21JANUARY 2002 37
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