The Boeing X-51 Waverider is an

unmanned An uncrewed vehicle or unmanned vehicle is a vehicle without a person on board. Uncrewed vehicles can either be under telerobotic control—remote controlled or remote guided vehicles—or they can be autonomously controlled—autonomous vehicl ...

research

scramjet A scramjet (supersonic combustion ramjet) is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow. As in ramjets, a scramjet relies on high vehicle speed to compress the incoming air forcefully ...

experimental aircraft for

hypersonic flight Hypersonic flight is flight through the atmosphere below altitudes of about 90 km at speeds greater than Mach 5, a speed where dissociation of air begins to become significant and high heat loads exist. Speeds of Mach 25+ have been achiev ...

at and an altitude of . The aircraft was designated X-51 in 2005. It completed its first powered hypersonic flight on 26 May 2010. After two unsuccessful test flights, the X-51 completed a flight of over six minutes and reached speeds of over Mach 5 for 210 seconds on 1 May 2013 for the longest duration powered hypersonic flight. ''

Waverider A waverider is a hypersonic aircraft design that improves its supersonic lift-to-drag ratio by using the shock waves being generated by its own flight as a lifting surface, a phenomenon known as compression lift. The waverider remains a we ...

'' refers in general to aircraft that take advantage of compression lift produced by their own

shock wave In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a me ...

s. The X-51 program was a cooperative effort by the

United States Air Force The United States Air Force (USAF) is the Aerial warfare, air military branch, service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part ...

DARPA The Defense Advanced Research Projects Agency (DARPA) is a research and development agency of the United States Department of Defense responsible for the development of emerging technologies for use by the military. Originally known as the Ad ...

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...

Boeing The Boeing Company () is an American multinational corporation that designs, manufactures, and sells airplanes, rotorcraft, rockets, satellites, telecommunications equipment, and missiles worldwide. The company also provides leasing and p ...

, and Pratt & Whitney Rocketdyne. The program was managed by the Aerospace Systems Directorate within the U.S.

Air Force Research Laboratory The Air Force Research Laboratory (AFRL) is a scientific research organization operated by the United States Air Force Materiel Command dedicated to leading the discovery, development, and integration of aerospace warfighting technologies, pl ...

(AFRL).

Design and development

In the 1990s, the Air Force Research Laboratory (AFRL) began the HyTECH program for hypersonic

propulsion Propulsion is the generation of force by any combination of pushing or pulling to modify the translational motion of an object, which is typically a rigid body (or an articulated rigid body) but may also concern a fluid. The term is derived f ...

. Pratt & Whitney received a contract from the AFRL to develop a hydrocarbon-fueled

engine which led to the development of the SJX61 engine. The SJX61 engine was originally meant for the NASA X-43C, which was eventually canceled. The engine was applied to the AFRL's Scramjet Engine Demonstrator program in late 2003.Warwick, Graham
"X-51A to demonstrate first practical scramjet"
. ''Flight International'', 20 July 2007. The scramjet flight test vehicle was designated X-51 on 27 September 2005. X-51A Waverider on B-52 2009

In flight demonstrations, the X-51 is carried by a

B-52 The Boeing B-52 Stratofortress is an American long-range, subsonic, jet-powered strategic bomber. The B-52 was designed and built by Boeing, which has continued to provide support and upgrades. It has been operated by the United States Air ...

to an altitude of about and then released over the Pacific Ocean. The X-51 is initially propelled by an MGM-140 ATACMS solid rocket booster to approximately . The booster is then jettisoned and the vehicle's Pratt & Whitney Rocketdyne SJY61 scramjet accelerates it to a top flight speed near ."X-51A Waverider flight planned for May 25"
. US Air Force, 20 May 2010. Retrieved: 20 May 2010. The X-51 uses

JP-7 Turbine Fuel Low Volatility JP-7, commonly known as JP-7 (referred to as Jet Propellant 7 prior to MIL-DTL-38219) is a specialized type of jet fuel developed in 1955 for the United States Air Force (USAF) for use in its supersonic military aircr ...

fuel for the SJY61 scramjet, carrying on board.

Applications for hypersonic technology

DARPA once viewed X-51 as a stepping stone to

Blackswift The DARPA Falcon Project (Force Application and Launch from Continental United States) is a two-part joint project between the Defense Advanced Research Projects Agency (DARPA) and the United States Air Force (USAF) and is part of Prompt Global ...

, a planned hypersonic demonstrator which was canceled in October 2008.Trimble, Stephen
"DARPA cancels Blackswift hypersonic test bed"
. Flight Global, 13 October 2008. In May 2013, the U.S. Air Force planned to apply X-51 technology to the High Speed Strike Weapon (HSSW), a missile similar in size to the X-51. The HSSW was expected to fly in 2020 and enter service in the mid-2020s. It was to have a range of , fly at Mach 5–6, and fit on an

F-35 The Lockheed Martin F-35 Lightning II is an American family of single-seat, single-engine, all-weather stealth multirole combat aircraft that is intended to perform both air superiority and strike missions. It is also able to provide elect ...

or in the internal bay of a B-2 bomber.

Testing

Ground and unpowered testing

Ground tests of the X-51A began in late 2005. A preliminary version of the X-51, the "Ground Demonstrator Engine No. 2", completed

wind tunnel Wind tunnels are large tubes with air blowing through them which are used to replicate the interaction between air and an object flying through the air or moving along the ground. Researchers use wind tunnels to learn more about how an aircraft ...

tests at the NASA Langley Research Center on 27 July 2006. Testing continued there until a simulated X-51 flight at Mach 5 was successfully completed on 30 April 2007. The testing is intended to observe

acceleration In mechanics, acceleration is the rate of change of the velocity of an object with respect to time. Accelerations are vector quantities (in that they have magnitude and direction). The orientation of an object's acceleration is given by t ...

between Mach 4 and Mach 6 and to demonstrate that hypersonic

thrust Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that sys ...

"isn't just luck".Coppinger, Rob.
Hypersonic X-51A gets December launch date
". '' Flight Global'', 6 August 2009. Retrieved: 29 April 2010. Four captive test flights were initially planned for 2009. However, the first captive flight of the X-51A on a B-52 was conducted on 9 December 2009,"X-51A WaveRider gets first ride aboard B-52"
. Edwards AFB News, 11 December 2009. with further flights in early 2010."X-51 getting ready for first flight"
. USAF Edwards AFB News, 4 March 2010.

Powered flight testing

The first powered flight of the X-51 was planned for 25 May 2010, but the presence of a cargo ship traveling through a portion of the

Naval Air Station Point Mugu Naval Air Station Point Mugu was a United States naval air station near Oxnard, California, which operated as an independent base from 1941 to 2000, when it merged with nearby Naval Construction Battalion Center Port Hueneme to form Naval Base ...

Sea Range caused a 24-hour delay. The X-51 completed its first powered flight successfully on 26 May 2010. It reached a speed of , an altitude of and flew for over 200 seconds; it did not meet the planned 300 second flight duration, however. The test had the longest hypersonic flight time of 140 seconds while under its scramjet power. The X-43 had the previous longest flight burn time of 12 seconds, while setting a new speed record of Mach 9.68. Three more test flights were planned and used the same flight

trajectory A trajectory or flight path is the path that an object with mass in motion follows through space as a function of time. In classical mechanics, a trajectory is defined by Hamiltonian mechanics via canonical coordinates; hence, a complete tra ...

. Boeing proposed to the Air Force Research Laboratory (AFRL) that two test flights be added to increase the total to six, with flights taking place at four to six week intervals, provided there are no failures. The second test flight was initially scheduled for 24 March 2011, but was not conducted due to unfavorable test conditions. The flight took place on 13 June 2011. However, the flight over the Pacific Ocean ended early due to an inlet

unstart In supersonic aerodynamics, an unstart refers to a generally violent breakdown of the supersonic airflow. The phenomenon occurs when mass flow rate changes significantly within a duct. Avoiding unstarts is a key objective in the design of the eng ...

event after being boosted to Mach 5 speed. The flight data from the test was being investigated. A B-52 released the X-51 at an approximate altitude of . The X-51's scramjet engine lit on ethylene, but did not properly transition to JP-7 fuel operation. The third test flight took place on 14 August 2012. The X-51 was to make a 300-second (5 minutes) experimental flight at speeds of . After separating from its rocket booster, the craft lost control and crashed into the Pacific. The Air Force Research Laboratory (AFRL) determined the problem was the X-51's upper right aerodynamic fin unlocked during flight and became uncontrollable; all four fins are needed for aerodynamic control. The aircraft lost control before the scramjet engine could ignite."August failure of Boeing X-51 likely due to fin, resonance"
. Flightglobal.com, 25 October 2012. On 1 May 2013, the X-51 performed its first fully successful flight test on its fourth test flight. The X-51 and booster detached from a B-52H and was powered to by the booster rocket. It then separated cleanly from the booster and ignited its own engine. The test aircraft then accelerated to and flew for 210 seconds until running out of fuel and plunging into the Pacific Ocean off Point Mugu for over six minutes of total flight time; this test was the longest air-breathing hypersonic flight. Researchers collected telemetry data for 370 seconds of flight. The test signified the completion of the program."Boeing X-51A WaveRider Sets Record with Successful 4th Flight"
. Boeing, 3 May 2013."Hypersonic X-51 programme ends in success"
. Flight International, 3 May 2013."X-51A Waverider Achieves Hypersonic Goal On Final Flight"
. Aviation Week, 2 May 2013. The Air Force Research Laboratory believes the successful flight will serve as research for practical applications of hypersonic flight, such as a missile, reconnaissance, transport, and air-breathing first stage for a space system."High-Speed Strike Weapon To Build On X-51 Flight"
. Aviation Week, 20 May 2013.

Specifications

References

External links

X-51 fact sheet on USAF site
*

Flight International, March 2009.
"Pratt & Whitney Rocketdyne Scramjet Excels in USAF Tests"
Aviation Week - subscription
YouTube video of FoxNews report, preceding test flight

YouTube video of test flight, shot from NASA chase plane
{{AFRL spacecraft X-51, Boeing X-51, Boeing X-51 X-51, Boeing X-51, Boeing Single-engined jet aircraft Aircraft with auxiliary rocket engines Air Force Research Laboratory projects Aircraft first flown in 2010