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Mystery Plane

AirVenture 2003 had its share of unusual aircraft on display, but none so unusual as the United States Air Force's version of the Long-EZ. There was nothing unusual about the airframe, but the powerplant had many of us scratching our collective heads.

Mystery Plane

On January 31, 2008, Scaled Composite's highly modified Long-EZ completed the first manned flight of an aircraft powered by a pulsed detonation engine (PDE). Five years of innovation and cooperation with the Air Force Research Laboratory (AFRL) and Innovative Scientific Solutions Inc. (ISSI) lead to this historic flight.

The engine powering the plane named Borealis consisted of four parallel tubes producing pulse detonations at a frequency of 80 Hz, creating up to 200 pounds of thrust (1,200 peak pounds per pulse, 200 average). A small rocket system was used to facilitate the liftoff of the Long-EZ, but the PDE operated under its own power for 10 seconds at an altitude of approximately 100 feet. No more flights are planned for the modified Long-EZ, but the success is likely to fuel more funding for PDE research. The aircraft itself has been moved to the National Museum of the United States Air Force for display.

Although used by Germany during World War II when Nazi engineers developed it to power the infamous V-1 (unmanned) missiles that blitzed England, pulsed detonation engines are still in their infancy. Some hope that this technology may become common as it matures as PD engines are less complicated and promise to be less expensive to operate than jet engines. Moreover, they offer a fuel savings of between 5-20 percent over traditional turbojet engines, but something has to be done about the noise.  

Mystery Plane

Engines normally burn fuel and air at subsonic speeds to provide propulsion. Pulsed detonation engines detonate the fuel-air mixture into repeated, controlled explosions, in this case timed by the use of a pair of automotive dual overhead cam aluminum cylinder heads. The resulting supersonic shockwaves create thrust. In this PD engine, the thrust is expelled through the four stainless steel tubes pointed out the rear of the plane. Remarkably (and, to some, obviously) the PD engine in this aircraft was assembled in part from off-the-shelf automotive, aircraft, and industrial parts.

Note:  In 2008, this aircraft was delivered to the National Museum of the United States Air Force and resides in the Research & Development Gallery.

For more images of the engine, see the photo gallery.

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