Air Force/Scaled Composites PDE Long-EZ heads for museum

Now that the U.S. Air Force has announced that yet another innovative Mojave product, a Long-EZ powered by a pulse-detonation engine (or PDE), is going to be enshrined in a national aviation museum, I thought it appropriate to dig out and share my images of this unique machine. The PDE was developed by a team from the Air Force Research Laboratory, and the Long-EZ was subsequently selected as an inexpensive testbed aircraft to try it out on. The engine was built by the team from "off-the-shelf automotive parts" in 2002.

What makes the PDE so unique is instead of burning fuel, called deflagration, to get propulsion, air and fuel are mixed, ignited and detonated in controlled explosions inside open-ended tubes that look like exhaust pipes. When detonation moves through the tubes it creates a supersonic shockwave that continually pulses and generates thrust.

Prior to the initial ground runs at Mojave, tenants were warned of the noise that the tests would make...and noisy it was! At well over half a mile away, the PDE sounded like a pipeless Harley on steroids parked right next to you. Development of the project continued on an on-and-off fashion for several years (the photos on the left and below were taken in 2004).

According to the Air Force press release which quotes Fred Schauer, AFRL Propulsion Directorate, "A major drawback that kept the team from flying earlier was the excessive drag caused from all the accessories hanging under the aircraft. This was overcome by placing an aerodynamic cowling over the PDE, which was designed by Scaled Composites. The engine also endured 100 hours of durability ground testing and 30 hours of airframe integration tests."
Finally, on January 31, 2008, the PDE-powered Long-EZ made its first and only flight, down Mojave's 12,500-foot Runway 12. The initial takeoff was by means of a small standard jet engine, and after the aircraft lifted free Scaled Composites test pilot Pete Siebold shut down the jet and fired off the PDE. The noise was unmistakeable, as the Long-EZ cruised at 60 to 100 feet over the runway, and hitting 120 knots. Just past the control tower and the main runway intersection, the PDE was shut off and Pete safely touched down and rolled to a stop before the end of the pavement. Though the aircraft had been towed out to Runway 12, it taxied back to Scaled's hangar under its backup jet engine power. The engine was developed and manufactured in-house by the AFRL Propulsion Directorate's Turbine Engine Division, Combustion Branch and its on-site contractor, ISSI. The successful flight test was a joint AFRL effort that included the activities of AFRL Propulsion Directorate for PDE developmental research and the propulsion package; AFRL Air Vehicles Directorate for structural, aero and acoustics; AFRL Human Effectiveness Directorate for exposure limits and acoustic protection, AFRL Materials and Manufacturing Directorate for structural materials; and Scaled Composites, Inc. for vehicle integration and flight testing.

Now, comes the announcement that after just the one flight, the record-setting plane will be displayed at the National Museum of the U.S. Air Force at Wright-Patterson AFB in Ohio. "The aircraft is in our restoration facility awaiting transfer for exhibit in our Experimental and Flight Test Gallery -- a most appropriate location for such a fine example of innovation," said senior curator Terry Aitken, National Museum of the U.S. Air Force, in their May 16th press release. So what's to come for PDE technology? "The increased thrust could be capable of powering future aircraft up to speeds of Mach 4, or four times the speed of sound, and beyond. According to Fred Schauer, AFRL Propulsion Directorate, the PDE can be combined with other engine cycles, such as turbines, rockets, or hypersonic scramjets, to optimize flight envelopes. 'This engine offers the capability of static to near hypersonic flight with good supersonic efficiencies. Pulsed detonation engines could make sense for missions that require efficient supersonic cruise and/or boost from low to high speeds,' Mr. Schauer said. Another plus for the engine is its ability to run on a variety of fuels and maintain near-constant-volume combustion, which makes it highly fuel efficient." Of course, they'll have to do something about that noise...it's rather far from the up-and-coming Stage 4 aircraft noise standards!

Click here for the complete Air Force press release.