Towards Silent Supersonic Planes

By Roland Piquepaille

There is no longer a single commercial supersonic airplane since the retirement of the Concorde last year. And even during its years of glory, the Concorde was not a commercial success, mainly because it was not allowed to cruise at supersonic speed over land. Why? Because of the sonic 'boom' which arises when you break the sound barrier. Now, a joint program between NASA, the military and the aerospace industry wants to remove, or at least reduce, this sonic boom, by changing the shape of supersonic planes. It seems to work. After a 'nose job' on a Northrop Grumman F-5E, about a third of the pressure released when breaking the sound barrier has already been suppressed.

Here are some short excerpts of this article from SPACE.com.

Under the Shaped Sonic Boom Demonstration program sponsored by Defense Advanced Research Projects Agency (DARPA), NASA and Northrop Grumman, researchers tacked on custom nose-glove on the front of Navy F-5E jet as well as an aluminum substructure.

The thunderous booms heard by humans when a vehicle flies overhead at speeds faster than the speed of sound -- about 758 miles (1,220 kilometers) an hour at sea level. The culprit is a change in air pressure -- about the same experienced by humans climbing a few floors of stairs, but much faster -- which makes the sounds audible.

The added volume on the modified F-5E, however, allowed researchers to better distribute the air pressure build-up in front of a supersonic plane, which shapes how the pressure is later released in a sonic boom shockwave as the aircraft breaks the sound barrier. Modifying that pressure release meant softer sonic booms.

On this photograph, you can see the modified F5-E Shaped Sonic Boom Demeonstration (SSBD) aircraft flying off the wing of the F-15B research testbed aircraft (Credit: Carla Thomas, NASA). [Note: If someone can identify the third plane on the lower left corner of the picture, please tell me what it is.]

A larger version of this photo is available here (660 KB).

So, will we soon travel in new commercial -- and silent -- supersonic planes? Not so fast.

The Dryden-shaped sonic boom flights were confined to an existing airplane that had already undergone modifications to reduce boom noise. But in order to tailor an aircraft to run as supersonic silent as possible, project researchers will ultimately have to build a prototype from the ground up.

But first, researchers need a new plane. The F-5E test plane used by NASA and Northrop Grumman was returned to the U.S. Navy and won't fly again for research. Dryden does have a stable of aircraft that could be used for the project.

For more information about the SSBD program, you also can read this news release from NASA's Dryden Flight Research Center.

And many other photographs are available in this SSBD Photo Collection.

Sources: Tariq Malik, SPACE.com, April 21, 2004; NASA's Dryden Flight Research Center website