Carlos Gonzalez, at Machine Design, reports on the latest developments in supersonic flight.
The Sonic Star reduces sonic boom by injecting plasma ahead of the shock wave. It uses plasma actuators built into the aircraft and powered by the S-MAGJET engines to ionize the air as it passes from forward to aft. The plasma airfoil gives the high pressure an escape route to travel around the aircraft instead of coming in direct contact, avoiding the creation of drag and shock waves.
Supersonic Flight: Overcoming the Sonic Boom
NASA and private companies are pushing research to reintroduce supersonic flight to the aerospace market.
Carlos Gonzalez Machine Design
Mar 23, 2015
The last commercial supersonic flight was the Concorde in 2003. The Concorde flew commercially starting in 1976, with seating for up to 128 passengers. Its cruising speed was 1,354 mph (2,179 km/h) with a Mach number of 2.04. Before that, the jet regularly flew from Singapore to London, New York to London, and from New York to Mexico City. But on its route to Mexico, it would have to fly at subsonic speeds while crossing over Florida because supersonic flight over land was—and still is—either banned or highly regulated in several countries, including the United States. To make supersonic flight legal for over-land routes, universities, private companies, and NASA are working to solve the problem of sonic booms (see “The Basics of Sonic Booms“).
In Search of a Quieter Boom
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Quiet Spike was tested as a method to reduce the initial shock wave created during supersonic flight. When breaking the sound barrier, the spike in front of the aircraft generates three small shockwaves before reaching the main body of the aircraft.
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During the days of the Concorde, many complained of the property damage created by sonic booms, let alone the noise pollution that many found intolerable. Between 1956 and 1968, over 38,000 claims were filed against the U.S. Air Force for damage wrought by sonic booms. As a result, since 1971, the Federal Aviation Administration (FAA) has prohibited supersonic flight over land. Also influencing that ban were concerns about the effects on the environment, including ozone depletion and climate change.
In 2001, NASA started the Shaped Sonic Boom Experiment to analyze sonic booms. They modified the fuselage of a Northrop F-5E Tiger II in an attempt to lower the effects of sonic booms during test flights. The nose of the F-5E was removed and replaced with a larger, longer version. The fairing under the fuselage was also lengthened and deepened.
The modified F-5E or Shaped Sonic Boom Demonstrator flew in 2003, and from that point, NASA took 1,300 sonic-boom measurements from various ground sensors. NASA engineers confirmed that the modifications led to an 18% reduction in initial pressure impulse and booms were an average of 4.7 decibels quieter compared to an unmodified F-5E.
NASA then moved on to the Sonic Boom Mitigation Project in 2005, which led to the introduction of the Quiet Spike. For this project, engineers at NASA’s Dryden Flight Research Center mounted a 24-ft. lance-like spike to the nose of an F-15B. The spike created three small shock waves that would parallel each other as they traveled to the ground. The smaller shock waves produce less sound compared to typical shock waves.
In 2007, the Quiet Spike F-15 reached supersonic flight with a Mach number high of 1.8. Test results confirmed predictions of the formation of smaller shock waves before the creation of a loud sonic boom, caused by rising pressure due to air coming in contact with the unmodified body of the F-15.
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A tip o’ the hat to The Silicon Graybeard.