Sonic Boom Modification May Lead To New Era

NASA and Northrop Grumman Corp. recently continued the quest to reduce the intensity of sonic booms by completing the collection of the largest set of sonic boom data recorded in 20 years. This effort is identifying and maturing technologies that could eventually enable unrestricted supersonic flight over land by future military and business aircraft, possibly ushering in a new era of supersonic flight.

"This represents the beginning of a new age in air transport, and we intend to capitalize on this breakthrough," said Richard Wlezien, manager of NASA's Vehicle Systems Program.

Last year, during the successful Shaped Sonic Boom Demonstration
(SSBD) project, a government and industry team proved the theory that by carefully altering the contours of a supersonic aircraft, the shockwave and its accompanying sonic boom can be shaped. That team included the NASA Langley Research Center, Hampton (VA), NASA's Dryden Flight Research Center at Edwards Air Force Base (CA), the Defense Advanced Research Projects Agency (DARPA) in Arlington (VA), and Northrop Grumman's Integrated Systems sector, El Segundo (CA).

"Northrop Grumman is proud to be able to contribute significantly to research that could revolutionize military and civil aircraft," said Charles Boccadoro, manager of Long Range Strike Systems for Northrop Grumman. "We will use the knowledge gained in these demonstrations to further our understanding of efficient supersonic flight."

Using the same specially-modified F-5E aircraft used in the earlier research flights, the renamed Shaped Sonic Boom Experiment team completed a second round of experiments, flying 21 supersonic flights at Mach numbers ranging from 1.35 to 1.4, and altitudes from 32,000 to 34,000 ft.

"It was very satisfying to be part of the team that collected this extensive set of data," said Peter Coen, supersonic vehicle sector manager for the NASA Vehicle Systems Program. "We now have the kind of information researchers need to really understand the details of sonic boom shaping in realistic flight conditions."

Several of the flights included NASA Dryden's F-15B research testbed aircraft flying in close formation with the F-5E to measure the details of the shockwave signature. During the flights, 45 shockwave patterns were measured by the F-15B at various distances and orientations from the F-5E. On other flights, an unmodified F-5E flew a few seconds behind the demonstration aircraft to provide a baseline sonic boom measurement to validate the reduced boom produced by the demonstrator. A USAF Test Pilot School Blanik L-23 sailplane carrying a microphone on the left wingtip, and a pressure transducer on the side of the fuselage, flew silently under the flight path of the F-5E at an altitude of 10,000 feet, in order to record sonic booms above the influence of most atmospheric turbulence.

In addition to the airborne data collected by the F-15B and the sailplane, sonic boom data was gathered on the ground by an array of 42 sensors and recording devices stretched out over 2 1/2 miles under the flight path of the F-5E. Dryden-developed boom amplitude and direction sensors, along with microphone recorders provided by Langley, Wyle Labs and Gulfstream Aerospace, recorded ground-level sonic boom signature data.

"We now have over 1,300 high-quality recordings of sonic booms," said Ed Haering, NASA Dryden's principal investigator for sonic boom research. "In all these flights the SSBD aircraft had shaped
(modified) sonic booms, with interesting differences in the shapes with variations of Mach number and altitude," Haering said.

NASA's Vehicle Systems Program funded this second round of flights. Northrop Grumman's Integrated Systems sector modified the U.S. Navy F-5E aircraft into the SSBD aircraft as part of the first round of flights,sponsored by DARPA's Quiet Supersonic Platform (QSP) program.

FMI: www.dfrc.nasa.gov