USAF Research Laboratory to re-attempt flights with experimental aircraft after making engine changes

Flight tests of an experimental aircraft powered by a pulse-detonation engine are to be retried by the end of this year, says the Ohio-based US Air Force Research Laboratory (AFRL). The engine has been improved to overcome development problems that prevented flights being attempted during initial tests at Mojave, California in late 2003 and early 2004.

“We had problems with the altitude at Mojave, and the resonance frequency,” says AFRL Propulsion Directorate research engineer and PDE specialist Fred Schauer. “Some days we’d go out on the runway and taxi fine, and others we’d go out and get no thrust at all.”

The AFRL’s prototype PDE has been reinstalled in a Scaled Composites-owned Long-Ez for the flight tests, and replaces a 100hp (75kW) Textron Lycoming 0-235 piston engine driving a pusher propeller.

The PDE consists of a Hirth auxiliary power unit with valve control through a heavily adapted General Motors Pontiac Grand Am Quad 4, 16-valve dual overhead camshaft automotive engine.

The detonation takes place in four tubes projecting from the back of the aircraft, and is designed to produce a combined force of around 100lb (0.45kN) thrust for flight speeds of 130kt (240km/h). In previous laboratory and ground tests, the engine has demonstrated thrust levels between 100lb and almost 200lb, says the AFRL.

The USAF, as with other branches of the US military, is interested in the potential of PDEs for a range of simple, cost-effective propulsion systems for supersonic and hypersonic missiles, possible replacement of conventional afterburners in combat aircraft engines, and as engines for both manned and unmanned aircraft. The concept is also being explored as a potential future combustion source for commercial and military gas turbines.

The PDE is an air-breathing engine with, in its simplest form, no moving parts. Combustion takes place in an open-ended tube in which fuel is mixed with air and detonated. The detonation wave travels down the tube at supersonic speed, generating thrust and, at the same time, reducing inlet pressure to allow fresh air and fuel to be drawn in. Each pulse lasts milliseconds.


Source: Flight International