OSHKOSH, Wis. -- Dr. Fred Shauer talks to Experimental Aircraft Association's AirVenture visitors about the pulsed detonation engine the Air Force Research Laboratory from Wright-Patterson Air Force Base, Ohio, has on display. The engine is a test bed for future engines that will be capable of powering aircraft to speeds of up to Mach 4. (U.S. Air Force Photo by Bill McCuddy)