|Artwork of X-51A Waverider in flight.
Image credit: US Air Force
The X-51 is a hypersonic flight program
run jointly by the US Air Force, DARPA, NASA, Boeing, and Pratt & Whitney
Rocketdyne. Its current demonstration vehicle is the X-51A Waverider
which carried out a successful maiden flight on May 26, 2010, becoming the
first aircraft to fly under power at speeds above Mach 5 for a sustained
period. A second flight, on March 24, 2011, ended early because of an engine
problem known as an "unstart". A third test flight took place on August
15, 2012, during which it was hoped the plane will reach Mach 6; however,
this also ended in failure when the vehicle broke up 15 seconds after the
rocket booster fell away.
|X-51A Waverider mounted under the
wing of a B-52. Image: US Air Force
The X-51A is air-launched from under the wing of a B52 Stratobomber. After
being dropped from the B-52, it fires a solid-rocket booster to accelerate
it to about Mach 4.5. The rocket booster is then jettisoned and the vehicle's
scramjet kicks in to push the vehicle to
hypersonic speeds of Mach 5–6. This scramjet, a Pratt & Whitney Rocketdyne
SJY61, was originally intended to be used by NASA's X-43A,
which was canceled.
The X-51A is not intended to be recovered after its mission, and falls in
the ocean. Only one X-51A remains of those originally built, and it has
not yet been decided if this will ever actually fly.
|X-51A Waverider specs
||25 ft (7.62 m)
||4,000 lb (1.814 kg)
||Mach 6 (3,600 mph; 5,800 km/h)
||460 miles 6 (740 km)
||70,000 ft (21,300 m)