The sound of silenceNASA working on sonic boom-less jets

Fifty years ago, in 1958, Robert Wise directed the classic war movie “Run Silent, Run Deep” (with Clark Gable and Burt Lancaster; it was also the film debut of Don Rickles). Soon they will be making a movie called “Run Silent, Run High.” Here is why. We wrote that other day about Yellow Jackets researchers developing a silent UAV (see 24 January 2009 HS Daily Wire). There are many benefits to bigger machines being silent, too. For example, NASA has announced the completion of a series of flight tests at Dryden Flight Research Center in Edwards, California, aimed at reducing the “sonic boom” effect, one of the major downsides of supersonic aircraft. Two custom-modified F-15 fighter jets were used in the test program, referred to by NASA as Lift and Nozzle Change Effects on Tail Shock (LaNCETS). Flying faster than sound, the lead F-15 used its custom-fitted canards (small winglets ahead of the main wings) to modify how much lift was generated by the main wing; it also changed its engine nozzle configuration.

Lewis Page writes that these changes altered the conical shockwaves trailing behind the plane, measured by the second F-15 using nose-mounted sensors to probe the wake of the jet just ahead. It is this shock front, trailing behind a supersonic aircraft, which produces the loud sonic boom when it hits the ground. The boom produced by Concorde was sufficient to restrict the Mach-2 airliner to subsonic speeds when over land, and meant that the London-New York route was the only one it could routinely serve.

It is not clear that there is a plan out there for another supersonic airliner right now, but some U.S. makers think there would be a market for supersonic business jets, able to fly billionaires and CEOs from continent to continent faster. Such jest would not be much use if they could not fly supersonic over land.

NASA has been working on fundamental research for a while, aiming to help the U.S. aviation industry solve the technical issues. One recent effort, for instance, saw Gulfstream “Quiet Spike” nose poles fitted to NASA jets, to see whether the shock cone from the spike might mask or mitigate the noise from the rest of the aircraft.

The just-completed LaNCETS effort uses a different approach, looking to find out how different lift loads and engine nozzle shapes affected the shape and intensity of the shock cones behind a plane. The chase F-15 used differential-GPS augmented satellite navigation kit to measure its position with respect to the lead craft exactly, allowing the sensor readings to be precisely mapped into a 3D database. The test results “will be made available to interested university and industry partners in order to further their research objectives”, according to NASA.