X-51A Scramjet Advances a Step Closer to Flight Clearance Published May 7, 2009 By Thomas Brown AFRL/RZ WRIGHT-PATTERSON AIR FORCE BASE, Ohio -- AFRL completed a series of ground tests on the SJX61-2, or X-2, the hydrocarbon-fueled scramjet [supersonic combustion ramjet] engine designated for flight clearance purposes by the X-51A Scramjet Engine Demonstrator program. The purpose of these latest program tests was to validate engine hardware and programming developed as an outcome of earlier testing. Eventually to undergo actual flight test, the ground-tested flight hardware incorporates all X-51A fuel system components, including engine flowpath, F119 full-authority digital engine control, closed-loop thermal management system, ethylene delivery system, and fuel pump. The success of this effort marks a critical achievement in the pursuit of X-51A integrated propulsion system flight clearance. Conducted at the National Aeronautics and Space Administration Langley Research Center's 8 ft high-temperature wind tunnel, this 12-week test activity focused on developing the engine's ignition sequence and demonstrating appropriate margins for handling off-design conditions, such as Mach number, dynamic pressure, and angle of attack. During testing, the engine accumulated 11.4 min of scramjet power-on time, an interval about twice the expected flight duration. Having built upon the successful results of many previous tests and extensive analyses, the X-51A program is now working to assemble the four flight test vehicles and finalize flight test planning in preparation for the technology's first flight.