THE X-51 Wave Rider
The Boeing X-51 (also known as X-51 WaveRider) is an unmanned scramjet demonstration aircraft for hypersonic (Mach 6, approximately 4,000 miles per hour (6,400 km/h) at altitude) flight testing. It successfully completed its first free-flight on 26 May 2010 and also achieved the longest duration flight at speeds over Mach 5.[1]
The X-51 is named "WaveRider" because it uses its shockwaves to add lift. The program is run as a cooperative effort of the United States Air Force, DARPA, NASA, Boeing, and Pratt & Whitney Rocketdyne. The program is managed by the Propulsion Directorate within the United States Air Force Research Laboratory (AFRL).[2] The X-51 had its first captive flight attached to a B-52 in December 2009.
In the 1990s, the Air Force Research Laboratory (AFRL) began the HyTECH program for hypersonic propulsion. Pratt & Whitney received a contract from the AFRL to develop a hydrocarbon-fueled scramjet engine which led to the development of the SJX61 engine. The SJX61 engine was originally meant for the NASA X-43, which was eventually canceled. The engine was applied to the AFRL's Scramjet Engine Demonstrator program in late 2003.[3] The scramjet flight test vehicle was designated X-51 on 27 September 2005.[4]
X-51A under the wing of a B-52 at Edwards Air Force Base, July 2009
In flight demonstrations, the X-51 is carried by a B-52 to an altitude of about 50,000 feet (15.2 kilometers) and then released over the Pacific Ocean.[5] The X-51 is initially propelled by an MGM-140 ATACMS solid rocket booster to approximately Mach 4.5. The booster is then jettisoned and the vehicle's Pratt & Whitney Rocketdyne SJY61 scramjet accelerates it to a top flight speed near Mach 6.[6][7] The X-51 uses JP-7 fuel for the SJY61 scramjet, carrying some 270 lb (120 kg) onboard.[8]
Previously, DARPA viewed X-51 as a stepping stone to Blackswift,[9] a planned hypersonic demonstrator which was canceled in October 2008.[10]
Initial testing
SJX61-2 engine successfully completes ground tests simulating Mach 5 flight conditions.
Ground tests of the X-51A began in late 2006. A preliminary version of the X-51, the "Ground Demonstrator Engine No. 2", completed wind tunnel tests at the NASA Langley Research Center on 27 July 2006.[11] Testing continued there until a simulated X-51 flight at Mach 5 was successfully completed on 30 April 2007.[12][13] The testing is intended to observe acceleration between Mach 4 and Mach 6 and to demonstrate that hypersonic thrust "isn't just luck".[14][15] Four test flights were initially planned for 2009, but the first captive flight of the X-51A on a B-52 was not conducted until 9 December 2009,[16][17] with further captive flights in early 2010.[18][19]
[edit]Powered flight tests
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 Sea Range caused a 24 hour postponement.[20] The X-51 completed its first powered flight successfully on 26 May 2010. It reached a speed of Mach 5, an altitude of 70,000 feet (21,000 m) and flew for over 200 seconds; it did not meet the planned 300 second flight duration, however.[1][21] The flight had the longest scramjet burn time of 140 seconds. The X-43 had the previous longest flight burn time of 12 seconds,[21][22][23] while setting a new speed record of Mach 9.8 (12,144 km/h, 7,546 mph).
Three more test flights were planned and will use the same flight trajectory.[22] Boeing proposed to the Air Force Research Laboratory that two test flights be added in order to increase the total to six, with flights taking place at four to six week intervals, assuming there are no failures.[24]
The second test flight was initially scheduled for 24 March 2011,[25] but was not conducted due to unfavorable test conditions.[26] The flight took place on 13 June 2011. However, the flight over the Pacific Ocean ended early due to an inlet unstart event after being boosted to Mach 5 speed. The flight data from the test is being investigated.[27] A B-52 released the X-51 at an approximate altitude of 50,000 feet. The X-51’s scramjet engine lit on ethylene, but did not properly transition to JP-7 fuel operation.[28]
The third test flight took place on 14 August 2012.[29] The X-51 was to make a 300 second, or 5 minute, experimental flight at speeds of five times the speed of sound, more than 3,600 mph.[30] After separating from its rocket booster, the craft lost control and crashed into the Pacific.[31] A statement by the Air Force Research Laboratory indicates a failure of the tail control surface as the cause.
General characteristics
Crew: None
Length: 25 ft in (7.62 m)
Empty weight: 4,000 lb (1,814 kg)
Performance
Maximum speed: Mach 6+ (3,600+ mph; 5,800+ km/h)
Range: 460 miles (740 km)
Service ceiling: 70,000 ft (21,300 m)
BUT THE
X-51 Waverider: Hypersonic jet ambitions fall short
The dreams of being able to fly from New York to London in under an hour are once again put on hold, as the latest effort to fly at over five times the speed of sound ends in failure.
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Will we fly at hypersonic speeds?
Work has begun on a passenger aircraft that could fly from Europe to Australia in four hours. Will it ever become a reality?
When Chuck Yeager broke the sound barrier in 1947, it ushered in a new era of high-speed air travel. Now, engineers are trying to make the next leap to craft that can fly more than five times the speed of sound. But it is proving difficult.
The most recent test flight ended in failure on Tuesday when a faulty control fin caused the US Air Force X-51 Waverider jet to lose control and crash into the Pacific Ocean.
The missile-like vehicle - powered by a supersonic combustion engine known as a scramjet - was dropped from a B-52 bomber off the coast of southern California It was supposed to be propelled by a solid-rocket booster, then ignite its scramjet engine to reach speeds of up to Mach 6. In the end, the test flight lasted just 31 seconds.
It was the last of three planned tests of the X-51, designed to demonstrate the feasibility of a hypersonic missile. It now joins a long list of failed hypersonic flights that show just how difficult it is to reach these so-called hypersonic speeds, usually defined as Mach 5 or above.
‘Rush to failure’
The appeal of hypersonics is simple: imagine an aircraft that can travel from New York to London in under an hour, or a missile that can reach anywhere in the world in less than two hours. But military experts have long cautioned that missiles, rather than reusable aircraft, are likely to be what will be developed first.
An air-to-air missile or an even an air-to-ground missile is the most likely near-term application for hypersonics, says Werner Dahm, director of Security and Defense Systems Initiative at Arizona State University, and a former US Air Force chief scientist. “It’s technologically much more achievable in the near to midterm,” he says.
Engineers have taken a variety of approaches to hypersonic aircraft over the years: the X-51 is called a WaveRider because it literally rides its own shock waves, and is powered by a scramjet, a variation of the traditional ramjet engine, where the exhaust from fuel combustion is compressed as it goes through the engine. But the Pentagon has also looked at a number of rocket-boosted gliders, and more complicated reusable aircraft powered by combination turbine and ramjet engines, among other designs.
But even building a test vehicle has proved difficult: the first X-51 flight test was cut short due to a flight anomaly, and the second test failed after the vehicle didn’t separate from its rocket, as planned. Yesterday’s failure is likely to raise even more questions about the future of hypersonic efforts. “Hypersonics test and evaluation is extremely unforgiving of miscalculation and error,” says Richard Hallion, a former senior advisor to the Air Force, and a leading expert on hypersonics.
Indeed, hypersonics has a mixed history, littered with the bodies of cancelled test vehicles, particularly those that have proved too ambitious. Hallion says many hypersonic research programs have suffered from a “rush to failure”, where flight vehicles have been flown too early, and then failed not because of an inherent problem in the vehicle, but because of a simple engineering mistake.
Most memorable, perhaps, was the 1980s-era National Aero-Space Plane, which was touted by President Ronald Reagan as a new Orient Express that could travel from Washington, DC to Tokyo in two hours, reaching speeds of up to 25 times the speed of sound. But the test aircraft, dubbed the X-30, proved too costly and vastly too complicated for the technology at the time.
More recently, the Defense Advanced Research Projects Agency (Darpa), the research and development arm of the Pentagon, tried to revive the idea of a reusable hypersonic aircraft through a program called Blackswift, though it was soon canceled, after Congress questioned the ability to engineer such an aircraft, given previous failures.
But that has not put them off the idea of hypersonic flight. The Pentagon also recently started work on the High Speed Strike Weapon, a hypersonic missile that will be launched from an aircraft. “It’s the next step,” says Mark Lewis, a former Air Force chief scientist, who was involved in the X-51 effort. “It’s looking at making hypersonics more operational and practical.”
Another programme is also underway: Darpa, which has also funded the X-51, held an open meeting this week for those interested in bidding on a new hypersonic program, which according to the agency announcement, is expected to lead to a hypersonic “X-plane” in 2016.
‘Monumental challenge’
The programme, however, is based on the design of the Falcon Hypersonic Test Vehicle-2, or HTV-2, an unmanned glider that can travel at speeds of up to Mach 20, but suffered two previous catastrophic failures. The HTV-2 was designed to be launched off a rocket, and then glide, unpowered. But in its first flight, the vehicle began to spin like a football eventually crashing; the second flight also failed.
HTV-2 was once considered as a candidate for a mission known as “Prompt Global Strike,” a weapon that could travel anywhere in the world within an hour.
For critics of the HTV-2, Darpa’s decision to continue with a vehicle that already failed twice in flight for apparent design failures is a repeat of mistakes made in previous hypersonic programmes. “It’s a bad design. It flew twice, it was lost twice,” says Hallion. “No matter how much lipstick you put on this pig, it’s still a pig.”
Some advocates of hypersonics, however, believe that the real problem with the government and military programmes is that they try to do much, and then simply cut off support when things go wrong. “You cannot achieve this until you commit yourself to doing it,” says Preston Carter, who previously managed hypersonics programs at Nasa, Darpa, and the Lawrence Livermore Laboratory in California,
Carter is now in the private sector trying to find funding for a commercial aircraft designed to travel at speeds of around Mach 5, which would make the trip from New York to London in about half the time that it took the Concorde.
Hypersonics is challenging, Carter acknowledges, but it’s not impossible. He points to previous aircraft, like the SR-71 Blackbird, a supersonic spy plane, and the civilian Concorde that, though not hypersonic, pushed the envelope of what was technically possible. Those aircraft also had seemingly monumental engineering challenges at the start, but they eventually succeeded, Carter says.
The same approach needs to be taken to hypersonic aircraft. “The reason why they were able to do it because they started,” he says. “The reason we won’t do it is because we haven’t started.”
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