DESIGN MIGHT BE BOOM TO AVIATION CHANGE COULD QUIET SUPERSONIC FLIGHTS.

Byline: Jim Skeen Staff Writer

PALMDALE - A modified Vietnam-era fighter jet is being readied at Air Force Plant 42 for tests to determine whether altering an aircraft's shape can reduce the intensity of sonic booms.

Starting next month, Northrop Grumman will conduct eight tests comparing the sonic booms of a standard F-5E fighter and the modified F-5E fighter fitted with a specially shaped forward fuselage. The tests will be conducted at NASA Dryden Flight Research Center at Edwards Air Force Base.

``Our objective is to show that by modifying the shape of an aircraft, the shape and behavior of shock waves - and, therefore, the intensity of a sonic boom - can be significantly altered,'' said Charles Boccadoro, Northrop Grumman's QSP program manager. ``This technology could eventually enable unrestricted supersonic flight over land.''

The demonstrations are part of Defense Advanced Research Projects Agency's Quiet Supersonic Platform program, aimed at developing technologies that will allow future high-speed military and business aircraft to operate with reduced sonic booms.

The program is not aimed at building an operational aircraft, but at providing technologies that could lead to new or improved bombers and fighters, reconnaissance aircraft and supersonic commercial aircraft, according to DARPA.

Such technologies would allow commercial and military aircraft to fly unrestricted over land rather than being restricted to certain test ranges or, as in the case of the Concorde passenger jet, being restricted to trans- Atlantic flights.

For the military, the technologies could lead to a small supersonic strike aircraft that would perform more missions per day, deliver more weapons on target and provide a rapid, long-range response capability, DARPA officials said.

The objectives of the QSP program are to create an aircraft that would weigh 100,000 pounds; cruise at speeds of Mach 2 to Mach 2.4, roughly between 1,400 mph and 1,680 mph; and have an unrefueled range of 6,000 miles.

By comparison, DARPA said, the Concorde weighs 400,000 pounds, cruises at Mach 2, and has an unrefueled range of 3,550 miles.

The program's goals are for the aircraft to create a sonic boom carrying an air pressure no greater than 0.3 pounds per square foot. A Concorde flying at an altitude of 50,000 feet creates a sonic boom of 1.94 pounds per square foot; a space shuttle returning to Earth causes a sonic boom of 1.25 pounds per square foot.

The sonic boom research, called the Shaped Sonic Boom Demonstration program, is jointly sponsored by DARPA, Northrop Grumman Corporation's Integrated Systems sector and the NASA Langley Research Center in Virginia.

For the sonic boom research, a Navy F-5E was outfitted with a specially shaped ``nose glove'' and the addition of aluminum substructure and composite skin to the underside of the fuselage. The aircraft performed three checkout flights at Northrop Grumman's St. Augustine, Fla. facility, where the modifications were made, before being flown to Palmdale.

The aircraft arrived in Palmdale last week for preparations for the research flights.