Supersonic Flight: NASA Centres Collaborate to Tackle Sonic Boom

This rendering shows the Lockheed Martin future supersonic advanced concept featuring two engines under the wings and one on top of the fuselage (not visible in this image).

Image Credit: NASA/Lockheed Martin

Since the Concorde’s final landing at London’s Heathrow Airport nearly a decade ago, commercial supersonic air travel has been as elusive as a piece of lost luggage.

However, this hasn’t stopped NASA from continuing the quest to develop solutions that will help get supersonic passenger travel off the ground once more and, while aerospace engineers have made significant progress in their understanding of supersonic flight, one significant challenge remains: the loud sonic boom.

Peter Coen

“There are three barriers particular to civil supersonic flight; sonic boom, high altitude emissions and airport noise. Of the three, boom is the most significant problem,” said Peter Coen, manager of NASA’s High Speed Project with the agency’s Aeronautics Research Mission Directorate’s (ARMD) Fundamental Aeronautics Program (FAP).

The level of concern over sonic boom annoyance became so significant that the Federal Aviation Administration prohibited domestic civil supersonic flight over land in 1973.

This prohibition helped quiet the skies and reduce potential impacts on the environment.

However, it also dashed hopes of introducing supersonic overland passenger service within U.S. airspace during the Concorde era.

Overcoming this sonic boom prohibition has kept engineers busy at the four NASA centers that conduct aeronautics research in California, Ohio and Virginia.

This rendering shows The Boeing Company's future supersonic advanced concept featuring two engines above the fuselage.

Image Credit: NASA/Boeing

Since the maximum acceptable loudness of a sonic boom is not specifically defined under the current FAA regulation, NASA and its aviation partners have been researching ways to identify a loudness level that is acceptable to both the FAA and the public, and to reduce the noise created by supersonic aircraft.

Using cutting-edge testing that builds on previous supersonic research, NASA has been exploring “low-boom” aircraft designs, and other strategies that show promise for reducing sonic boom levels.

Previous research by NASA, the military and the aircraft industry has determined that a variety of factors, from the shape and position of aircraft components to the propulsion system's characteristics, determine the make-up of a supersonic aircraft's sonic boom.

Therefore, engineers are able to tune or “shape” a boom signature through design to minimize the loudness of the boom it produces in flight.

The most recent possible supersonic aircraft designs reflect what's needed to meet NASA's low-boom requirements.

These requirements specify targets for boom loudness, aerodynamic efficiency, and airport noise for an N+2, second generation beyond current technology, aircraft design that could be flying by the years 2020 through 2025.

Similar to designs of the past, the current concepts are characterized by a needle-like nose, a sleek fuselage and a delta wing or highly-swept wings. It’s the details of how those designs are shaped that result in the reduced sonic boom.

One design, proposed by industry partner Lockheed Martin, mounts two engines under the wing in a traditional configuration with one additional centerline engine above the wing.

The other industry partner currently working with the NASA High Speed Project, The Boeing Company, proposes two top-mounted engines in a departure from historical aircraft design.

Read the full article here

Aerion: Are there supersonic business jets (SSBJ) in the future

Could supersonic travel be available again before then? 

Quite possibly, if Aerion has anything to do with it and it will be in the form of supersonic business jets (SSBJ). 

Several companies have been working on these concepts, and while the credit crunch of 2008 slowed down progress, now it looks possible that an SSBJ could be in service by the end of the decade.

It should be a lot easier to get an SSBJ project off the ground. A smaller SST is less complex, and could use off-the-shelf components such as engines, so development costs should be lower.

In addition, advances in materials, especially carbon composites, mean advanced aerodynamics can now be converted from the CAD-CAM computer to reality.

For the business customer, the appeal is clear. Rather than being tied to an airline schedule, you can fly wherever – and whenever you want.

So even if an SSBJ wouldn’t quite match Concorde’s Mach 2 performance, the door-to-door time is likely to be much faster.

And aircraft manufacturers may find it easier to persuade multinational CEOs to buy SSBJs as a productivity tool than to convince the stony-faced airline accountants to invest millions in a fleet of supersonic airliners.

The race is on
Leading the race to get the first SSBJ to market is Aerion, which unveiled its radical concept in 2007.

Unlike most SST designs, the Aerion SBJ has been designed to operate subsonically as well as supersonically.

It uses supersonic laminar flow wings – short, unswept wings, rather than delta wings favoured by most SST concepts.

Aerion says this gives it the ability to cruise smoothly at just below the sound barrier, as well as supersonically at its maximum speed of Mach 1.6.

The subsonic performance is necessary as it is still illegal to operate supersonically over many land areas – such as the US, or western Europe.

With a range of around 7,500km it would be possible to fly directly from, say, Frankfurt to Chicago – flying subsonically over land and supersonically over sea.

This would take less than five hours, compared with around nine hours by conventional subsonic jet.

The Aerion SBJ uses carbonfibre composites for the wings, and a section of the wing has been tested successfully already, mounted underneath one of Nasa’s Boeing F-15 supersonic test planes.

As a result of its straight wing design and full-span flaps, typical approach speed will be 120 knots, similar to a regular bizjet, and the aircraft will be able to operate routinely from business airports with 2,000m-long runways – removing the need to join security queues at major airports.