The X-51A Waverider hypersonic test aircraft reached Mach 5.1 during its fourth and final flight earlier this month, traveling 230 nautical miles in just over six minutes over the Pacific Ocean.
“It was a full mission success,” said Charlie Brink, the X-51A programme manager for the US Air Force Research Laboratory Aerospace Systems Directorate.
The aircraft travelled more than 230 nautical miles in just over six minutes over the Point Mugu Naval Air Warfare Center Sea Range, California, on May 1. It was the longest of the four X-51A test flights and the longest air-breathing hypersonic flight ever.
“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,” Brink said.
“This demonstration of a practical hypersonic scramjet engine is a historic achievement that has been years in the making,” said Darryl Davis, president, Boeing Phantom Works. “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.”
The X-51A took off from the Air Force Test Centre at Edwards AFB, California, under the wing of a B-52H Stratofortress bomber. It was released at approximately 50,000 feet and accelerated to Mach 4.8 in about 26 seconds powered by a solid rocket booster. After separating from the booster, the cruiser’s supersonic combustion ramjet, or scramjet, engine then lit and accelerated the aircraft to Mach 5.1 at 60,000 feet.
After exhausting its 240-second fuel supply, the vehicle continued to send back telemetry data until it splashed down into the ocean and was destroyed as designed. At impact, 370 seconds of data were collected from the experiment.
“This success is the result of a lot of hard work by an incredible team. The contributions of Boeing, Pratt and Whitney Rocketdyne, the 412th Test Wing at Edwards AFB, NASA Dryden and DARPA were all vital,” Brink said.
This was the last of four test vehicles originally conceived when the $300 million technology demonstration program began in 2004. The program objective was to prove the viability of air-breathing, high-speed scramjet propulsion.
The X-51A is unique primarily due to its use of a hydrocarbon fuel in its scramjet engine. Other vehicles have achieved hypersonic, generally defined as speeds above Mach 5, flight with the use of hydrogen fuel. Without any moving parts, hydrocarbon fuel is injected into the scramjet’s combustion chamber where it mixes with the air rushing through the chamber and is ignited in a process likened to lighting a match in a hurricane.
The use of logistically supportable hydrocarbon fuel is widely considered vital for the practical application of hypersonic flight.
As a technology demonstration programme, there is no immediate successor to the X-51A programme. However, the US Air Force will continue hypersonic research and the successes of the X-51A will pay dividends to the High Speed Strike Weapon programme currently in its early formation phase with AFRL.