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The US Air Force has been developing an aircraft that employs an air-breathing scramjet engine, and hopes to run test flights in the fall of 2009. Officials hope the X-51 “Waverider” aircraft will provide high speed aircraft for reconnaissance or strike missions, and eventually the engines will be used for rockets to deploy satellites in space.

“The long-range goal of this for the Air Force is access to space,” said Charlie Brink, an Air Force Research Laboratory propulsion directorate official who manages the X-51 program from Wright-Patterson Air Force Base.



The first test flight of the X-51 will be on Oct. 27, 2009, launched from a B-52 aircraft with a missile booster to at least Mach 4.5, the minimum speed at which the air-breathing scramjet engine operates, before the scramjet kicks in and accelerates the vehicle to at least Mach 6 — six times the speed of sound. The Air Force Research Laboratory expects that the aircraft will fly for about five minutes before crashing into the Pacific. The October flight — and three separate test flights planned in early 2010 — are designed to demonstrate the practicality of using the air-breathing scramjet engine to power and control an aircraft at hypersonic speeds (Mach 5 or greater). The $246.5 million development program has been under development since December 2003.

Scramjet is an acronym for Supersonic Combustion Ramjet. A ramjet has no moving parts and achieves compression of intake air by the forward speed of the vehicle. The scramjet differs from the ramjet in that combustion takes place at supersonic air velocities through the engine. It stays aloft, in part, with lift generated by the shock waves of its own flight. It is mechanically simple, but vastly more complex aerodynamically than a jet engine. Hydrogen is normally the fuel used.

In 2004, NASA conducted flight tests of a hydrogen-based scramjet engine which reached speeds of Mach 9.6, or nearly 7,000 mph, powering an aircraft known as the X-43. However, none of the vehicles survived a flight test.

Brink compares the work of developing the scramjet — to complement aircraft turbine engines and rockets — with aviation’s earlier transition from propellers to jet engines. Air Force leadership will decide the scramjet program’s next step, depending on how the project turns out, Brink said.

Lead Photo Caption: Charlie Brink, manager of the Air Force’s X-51 “Waverider” scramjet research project stands with a scale model of the hypersonic aircraft. Credit: Ty Greenlees Dayton Daily News

Source: Dayton (OH) Daily News