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March 25, 2002

Release: 02-17

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NASA is part of a team seeking quieter sonic booms. NASA's F-15B Research Testbed aircraft recently flew in the supersonic shock wave of a U.S. Navy F-5E in support of the F-5 Shaped Sonic Boom Demonstration (SSBD) project, part of the Defense Advanced Research Projects Agency's (DARPA) Quiet Supersonic Platform (QSP) program.

The flights originated from the NASA Dryden Flight Research Center at Edwards, Calif.

Four flights were flown in order to measure the F-5E's near-field (close-up) sonic boom signature at Mach 1.4, during which more than 50 shockwave patterns were measured at distances as close as 100 feet below the F-5E.

The F-15B's specially-instrumented noseboom recorded static pressure measurements while flying behind and below the F-5E. This provided a baseline measurement of the F-5E's sonic boom characteristics. Differential Global Positioning System (GPS) receivers on both aircraft yielded relative aircraft position.

Northrop Grumman Corporation's Integrated Systems sector of El Segundo, Calif., intends to modify the F-5E aircraft into a Shaped Sonic Boom Demonstrator in an effort to reduce its sonic boom. The U.S. Navy aircraft is based at Fallon Naval Air Station in Fallon, Nevada. The data provided by Dryden's F-15B is assisting Northrop Grumman's and DARPA's efforts, as well as helping assess SSBD flight test techniques.

In addition to the airborne data collected by the F-15B, sonic boom data was gathered on the ground by two Dryden-developed Boom Amplitude and Direction Sensors (BADS) in order to obtain ground-level sonic boom signature data. Twenty-five sonic booms from the F-5E and F-15B were recorded.

Dryden has expertise in air and ground-based sonic boom measurement techniques, having accomplished several sonic boom studies over the years. In 1995, Dryden's F-16XL-1 aircraft probed the shockwave of one of Dryden's SR-71 aircraft.

"The flight data show fine details unseen in the preflight predictions," said Ed Haering, Dryden's principal investigator for sonic boom studies. "Based on these details, the Computational Fluid Dynamic (CFD) grid density was increased. Preliminary flight data agree well with the CFD predictions over most of the region, with an adjustment needed to the predictions in the region of the engine inlet. These flight data allow the QSP team to validate prediction tools to design aircraft with lower sonic booms," Haering said.

DARPA and Northrop Grumman plan to fly the F-5E in the fall with a special fairing designed to reduce the aircraft's sonic boom. Dryden's F-15B will again fly in the Shaped Sonic Boom Demonstrator's shock waves to record changes produced by the F-5E modifications.


Note to Editors: High resolution photos of the F-15B and F-5E are available on-line at: /centers/dfrc or by calling Gray Creech at (661) 276-2662.

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