It's not every day a new form of propulsion makes its first flight: the turbojet in August 1939 (Heinkel He178), the ramjet in April 1949 (Leduc 010), the scramjet in July 2002 (University of Queensland HyShot). Now it's the turn of the pulsed detonation engine (PDE) - a simple, lightweight powerplant that promises efficient operation over a wide range of speeds from 0 to Mach 4.
In a PDE, combustion is supersonic (detonation) rather than subsonic (deflagration), resulting in the more efficient conversion of fuel into thrust. PDEs have few moving parts. A fuel/air mixture is injected into a tube and ignited, creating a supersonic detonation wave that travels down the tube and is expelled, producing a pulse of thrust. Grouping several tubes together and firing each many times a second produces constant thrust.
It's taken a few years longer than planned, but the US Air Force Research Laboratory and partners ISSI and Scaled Composites finally accomplished the first PDE-powered flight in late January. The modified Long-EZ was powered by a four-tube PDE, each tube firing 20 times a second, producing 200lb peak thrust. The flight was short, just a few tens of seconds, taking place within the length of the Mojave runway, but it was a first.
(Pictures by Alan Radecki)