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Northrop Grumman's modified F-5E Shaped Sonic Boom Demonstration aircraft flies off the wing of NASA's F-15B research testbed aircraft. The F-15B flew in the supersonic shockwave of the F-5E as part of the sonic boom demonstration project.
NASA Photo / Carla Thomas |
Boom!
Dryden assists Northrop in sonic boom research
By Gray Creech
Aerospace Projects Writer
In efforts to reduce problems created by supersonic flight over land, Dryden researchers recently played vital roles in the airborne and ground measurement of a shaped sonic boom.
Dryden-designed ground sensors measured shock wave intensity and propagation on the ground while Dryden's F-15B research testbed aircraft flew in the supersonic shock waves of a Northrop Grumman Corp.—modified U.S. Navy F-5E in support of the Shaped Sonic Boom Demonstration (SSBD) project.
The SSBD project is part of the Defense Advanced Research Projects Agency's (DARPA) Quiet Supersonic Platform (QSP) program, an ongoing effort to identify and mature tech-nologies that could allow future military and business aircraft to operate with reduced sonic boom.
The SSBD project objective is to show that by modifying the shape of an aircraft, the shape and behavior of supersonic shock waves can be significantly altered, thereby reducing the intensity of sonic booms. This technology could eventually enable unrestricted supersonic flight over land, long a major stumbling block for both commercial and military applications because of population impact.
During the demonstration, the F-15B flew two flights through the Edwards Air Force Base supersonic corridor behind the modified F-5E in order to measure that aircraft's near-field (close-up) sonic boom signature, during which many shockwave patterns were measured. These data will be compared to computational predictions of the shock waves.
"The SSBD project has been a collaborative effort between multiple government agencies and private industry," said David Richwine, Dryden's SSBD project manager. "As a SSBD team member, NASA Dryden was able to contribute several key areas of expertise, capabilities and aircraft that were vital to the overall success of the SSBD program."
The F-15B's specially instrumented nose boom recorded static pressure measurements while flying behind and below the modified F-5E at a speed of about Mach 1.4. Differential carrier-phase Global Positioning System (GPS) receivers on both aircraft yielded relative aircraft positions ranging from 100 to 500 feet. This maneuver provided the required measurements to properly characterize the modified F-5E's sonic boom characteristics.
The F-15B also flew baseline probe flights in 2002 in support of the SSBD project, providing measurements of an unmodified F-5E to validate the near-field sonic boom signature predictions.
In addition to airborne data collected by the F-15B, sonic boom data were gathered on the ground by two Dryden-developed Boom Amplitude and Direction Sensors (BADS) in order to obtain ground-level sonic boom signature data.
On three other flights, the modified F-5E was followed 45 seconds later by an unmodified F-5E to determine the effect of aircraft shaping on sonic booms. The BADS measured the world's first shaped sonic boom, followed by the normal, unshaped sonic boom from the unmodified F-5E.
"By having the near-field probing data from both the unmodified and now the modified F-5E aircraft, we can validate the design tools required for a new class of quieter supersonic aircraft," said Edward Haering, Dryden's principal investigator for the SSBD project. "The ground-level sonic boom recordings we gathered with the modified and unmodified aircraft validates that the shaped sonic boom theory works with real aircraft through the real atmosphere."
Dryden's F/A-18 aircraft provided safety and photo chase for the modified F-5E during four supersonic envelope expansion flights and two research flights.
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 the Center's SR-71 aircraft.
The SSBD project is jointly sponsored by DARPA, Northrop Grumman Corp.'s Integrated Systems Sector and NASA's Langley Research Center, Hampton, Va.
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