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A new supersonic probe seen affixed to a F-15B flight test fixture might one day measure the sonic booms of a new generation of supersonic aircraft. (NASA/Lauren Hughes)

Probing ways to dampen sonic boom

One of the reasons there is not a supersonic plane flying in and out of an airport near you is because of that not-so-little thing known as a sonic boom. And that particular reason also has a lot to do with there not being more supersonic aircraft programs for commercial purposes over the years.

But as airlines strive to move more and more people faster and faster, the talk of a future supersonic aircraft for commercial purposes is getting louder and louder. NASA is part of that conversation and is involved in a number of projects to make supersonic, and hypersonic, flight viable again.

To that end, NASA Armstrong Flight Research Center is involved in flight tests with an air data probe on an F-15B aircraft in California to further research sonic booms, and ultimately find ways to control and lessen the noise from shockwaves so that federal regulators will allow commercial supersonic flight overland.

A series of six flights were set to continue throughout March. As with earlier flight tests in 2011 and 2014, an Eagle Aero Probe is flying on the F-15B's test fixture called the centerline instrument pylon. The pylon is located under the aircraft's fuselage.

Researchers will be evaluating the performance of the probe originally developed by Eagle Aeronautics and redesigned by NASA for this phase. The probe will be tested in a flight environment and the results will be compared with a traditional NACA-style probe that was flown on the centerline instrumented pylon in 2012. In addition to obtaining air data measurements underneath the F-15B, the probe will measure the strength of a shockwave generated from, as of yet, an undetermined part of the F-15B aircraft structure.

"You want to have minimal lag in your measurement system to accurately characterize the intensity of the shockwave," said Mike Frederick, NASA Armstrong Principal Investigator of the Eagle Aero Probe. "With this probe, pressure changes are seen almost immediately because the pressure sensors are located within about four inches of the pressure ports on the nosecone. For comparison, on the F-15B nose boom, which has been used for air-to-air probing in the past, the pressure transducers are located back in the radome, approximately 15 feet behind the pressure ports."

A later phase of the testing will be to install the probe on either the nose of the F-15B, or on one of NASA's F-15D aircraft based at Armstrong, said Brett Pauer, F-15B Project Manager, adding that the Eagle Aero Probe will replace the current nose boom during shockwave probing research flights.

The later flights will look at shockwaves generated by another nearby supersonic aircraft and are expected to obtain more accurate data than traditional probes. "If the flights go as planned, the Eagle Aero Probes could be used to measure the shockwaves generated by future supersonic aircraft," Pauer said. "This data could help improve aircraft design tools that would ultimately reduce the loudness of sonic booms."

Previous generations of the Eagle Aero Probes flew on the F-15B as part of a continuing effort that began as a NASA Research Announcement effort in 2009. The probes were tested in the Unitary Plan Wind Tunnel at NASA's Langley Research Centerprior to flight research at NASA Armstrong.

From the data obtained during this current flight phase, a key deficiency with the previous generations of the probe appears to be solved, Frederick said. A heater control system added into the probe keeps the pressure transducer temperatures stable at 150°F, minimizing temperature effects on the pressure transducers and resulting in more accurate pressure measurements.


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