The USAF launched the last of its four experimental X-51A Waverider vehicles Wednesday. Officials say the vehicle reached a speed of Mach 5.1, travelling more than 230 nautical miles before crashing into the Pacific off the California coast as planned.
The Air Force says the X-51A Waverider achieved the longest hypersonic flight by a jet-fuel powered aircraft when it flew for three-and-a-half minutes at more than five times the speed of sound.
Charlie Brink, X-51A program manager for the Air Force Research Laboratory Aerospace Systems Directorate, said in a statement: "It was a full mission success."
The vehicle was launched from Edwards Air Force Base in California, carried under the wing of a B-52H Stratofortress. It was released at an altitude of about 50,000 feet (15,000 meters).
After release, it accelerated to Mach 4.8 in about 26 seconds, powered by a solid rocket booster built by Pratt & Whitney Rocketdyne of United Technologies. After separating from the booster, its air-breathing supersonic combustion ramjet (scramjet) engine accelerated it to Mach 5.1 at 60,000 feet. After the fuel supply of the scramjet burned up, the vehicle crashed into the Pacific Ocean. The impact of the splash destroyed the vehicle.
The video shows the Waverider detaching from under the left wing of the B-52 bomber at an altitude of about 50,000 feet. It transmitted a total of 370 seconds of data to the control station at Edwards Air Force Base in California before it crashed into the Pacific
The Air Force said after the test that there are no plans to build any more X-51A experimental vehicles. Officials said the four experimental vehicles were built not as prototype for new weapons systems but to demonstrate hypersonic jet-fuelled flight technology. According to officials, the $300 million experimental project provided useful technical lessons for future hypersonic weapons, surveillance and reconnaissance systems.
Photo released by the U.S. Air Force, the X-51A Waverider, carried under the wing of a B-52H Stratofortress bomber
Brink said: "I believe all we have learned from the X-51A Waverider will serve as the bedrock for future hypersonics research and ultimately the practical application of hypersonic flight."
TVNZ reports Darryl Davis, president of Phantom Works, Boeing's advanced research and prototyping arm, said: "This demonstration of a practical hypersonic scramjet engine is a historic achievement that has been years in the making. This test proves the technology has matured to the point that it opens the door to practical applications, such as advanced defence systems and more cost-effective access to space."
Hypersonic flight is defined specifically as flight through the atmosphere at speeds above Mach 5.5, a speed where disassociation of air begins to become significant and high heat loads exist. However, the term is used generally to describe any flight that reaches speeds above Mach 5.
Hypersonic vehicles are usually powered by hydrogen propellant, but according to the Air Force in a press release, X-51A is unique because of the use of hydrocarbon fuel in its supersonic combustion ramjet, or scramjet, engine. The scramjet works using hydrocarbon fuel injected into its combustion chamber where it mixes with the air rushing through the chamber and is ignited in the process.
Other vehicles have achieved hypersonic flight using hydrogen fuel.
The X-51A's first test flight occurred in May 2010. The vehicle flew for more than three minutes, reaching a top speed of Mach 4.88. The next two flight attempts in June 2011 and August 2012 failed.
According to Aviation Week, the latest flight incorporated improvements and lessons from the previous successful and failed flights, including better sealing between interfaces in the engine flow-path. Inadequate sealing in previous failed flights allowed hot gases into the vehicle’s interior. The latest flight also included changes to the hardware and software to correct problems that led to failure in the second flight.
The US military is studying hypersonic flight in order to develop weapons capable of hitting targets anywhere on Earth within an hour. Digital Journal reported in November 2011 that "... the US conducted a successful flight test of a prototype of a new weapon, a 'glide vehicle,' that travels five times faster than sound. The Advanced Hypersonic Weapon was launched from the U.S. Pacific Missile Range Facility in Kauai, Hawaii... Advanced Hypersonic Weapons (AHW) are designed for hitting long range targets within the earth's atmosphere at speeds at least five times the speed of sound (3,805 mph or 6,124 kph, at sea level)."