NASA has successfully tested a new technique that will prove its planes can fly faster than the speed of sound without producing a sonic boom, potentially halving current commercial flight times.
The space agency has photographed sonic shockwaves using cutting-edge solar technology in preparation for the 2022 flight of its newest experimental stealth plane. NASA needs to prove the next-generation craft are quiet before it can roll out the technology.
Battling the Sonic Boom
When a plane travels faster than the speed of sound, it makes shockwaves shoot to the ground below in a violent sonic boom. NASA has been developing low-boom flight demonstration aircraft, or LBFD, which can travel faster than the speed of sound without the boom.
LBFD planes were announced as one of NASA's new X-planes in 2016. These experimental aircraft are intended to "push back the frontiers of aviation," NASA reported at the time. Earlier this year, NASA took manufacturing bids from commercial companies wanting to construct the planes.
NASA engineers used a technique called Schlieren photography to capture the planes and their shockwaves. Using three telescopic cameras and a special hydrogen alpha filter, shockwaves appear eclipsed against the sun.
"There are different concentrations of hydrogen atoms caused by varying magnetic fields on the sun's surface, and where there's a higher concentration of hydrogen atoms, we see more light, while lower concentration shows less light," principal investigator Mike Hill explained in the press release. "The hydrogen alpha filter works by allowing only the wavelength of light, emitted by hydrogen on the sun's surface, through."
100-Foot Window for Success
Last year, NASA used the same technique on planes at an altitude of 40,000 feet in the first BOSCO (background-oriented Schlieren using celestial objects) test. LBFD planes, however will be flying at altitudes of up to 60,000 feet. This means their cameras will need an upgrade.
Rather than taking photos from the ground, a smaller camera system will take photos from onboard these high-altitude planes. The BOSCO II test has successfully validated this new technology.
Taking pictures onboard also means that the cameras will need a much smaller range than from the ground. The air-to-air photography system needs to have a range of about 10,000 feet. In BOSCO II, the supersonic pilots had to transition from subsonic speeds at a specific point between the cameras on the ground and the sun, all at an altitude of 10,000 feet to mirror the air-to-air distance. This gave pilots a target measuring only around 100 feet in diameter.
"This wasn't an easy task for our pilots, but they hit the mark," Commercial Supersonic Technology Subproject Manager Brett Pauer said in the press release. "In the first series of BOSCO flights, we were trying to hit a spot that was about 300 feet in diameter. For these flights, however, since we had to shoot at a closer range, we needed to hit a spot that is one quarter of that. We're talking about a spot in the sky that's under 100 feet in diameter."
This time around, the team tested the camera with U.S. Air Force Test Pilot School T-38 aircraft and a NASA F-15. The scientists hope to replicate the technique with the LBFD aircraft in the future. This will allow them to show just how quietly these experimental aircraft can fly.
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