X-51 Scramjet Engine Demonstrator - WaveRider (SED-WR)

On 1 May 2013, the final flight of the X-51A Waverider test program was accomplished over the Pacific Ocean. The final flight saw the remaining test vehicle reaching Mach 5.1 and traveling more than 230 nautical miles in just over 6 minutes over the Point Mugu Naval Air Warfare Center Sea Range, California. This was the longest of the 4 X-51A test flights and the longest air-breathing hypersonic flight ever at that time. The vehicle was released at approximately 50,000 feet and accelerated to Mach 4.8 in approximately 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. The vehicle was the last of 4 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. As a technology demonstration program, there was no immediate successor to the X-51A program. However, the Air Force would continue hypersonic research and the successes of the X-51A were expected to pay dividends to the High Speed Strike Weapon program then in its early formation phase with Air Force Research Laboratory.

The X-51 Scramjet Engine Demonstrator Waverider Program is an advanced hypersonic propulsion development effort funded by the Air Force Research Laboratory (AFRL) and the Defense Advanced Research Projects Agency (DARPA). The X-51A Flight Test Program plans to demonstrate the scramjet engine within the Mach 4.5 to 6.0+ range with four flight tests beginning in 2009. The program will set the foundation for several hypersonic applications, including access to space, reconnaissance-strike and global reach.

The first flight 26 May 2010 set a record for duration at hypersonic speed. The flight was about 10 times longer than any previous hypersonic scramjet flight and "80 to 90 percent" of flight test objectives were achieved. By that time, it was estimated that $200 million had been spent on the program. Program officials said 15 March 2011 that the Air Force planned to fly its second X-51A Waverider hypersonic flight test demonstrator as early as 22 March 2011. During the test attempt in March, the scramjet failed to release from the B-52 and the team went to work to create a solution.

A B-52H Stratofortress on loan to Edwards released the experimental vehicle from an altitude of approximately 50,000 feet 13 June 2011. After release, the X-51 was initially accelerated by a solid rocket booster. The hypersonic aircraft was successfully boosted to just over Mach 5 and the scramjet engine lit, but it failed to transition to full power. The second X-51 supersonic combustion scramjet test vehicle actually produced more thrust than expected before the test flight ended in failure. Although the second flight test of the X-51A Waverider scramjet ended prematurely, the coordination and performance of the Hypersonics Combined Test Force and the 419th Flight Test Squadron was flawless. This second flight ended with a controlled landing into the ocean.

There is also a fourth test vehicle available that could be used for materials testing or different flight profiles testing. AFRL is hoping to embark up on a new "robust scramjet" project, which would create a normal fighter-sized engine.

The X-51A was not designed to be a weapon, but its success as a technology demonstrator may soon enable the transition of technologies to a new class of hypersonic weapon systems. There are a number of initiatives in the works, but none had been decided upon and there currently is no program of record for a hypersonic strike or ISR aircraft based upon the Waverider.

In a letter dated 27 September 2005, the US Air Force (HQ USAF/XPPE) officially granted the US Air Force Research Laboratory (AFRL) Propulsion Directorate's scramjet flight test vehicle the designation X-51A. Since the introduction of the legendary X-1 in 1946, scientists have used the X-plane designations to identify experimental aircraft and rockets used to explore new aerospace technologies. The Propulsion Directorate was working with Pratt & Whitney (P&W)/Rocketdyne's Space Propulsion Division and Boeing's Transformational Space Systems Division to design the X-51A scramjet powered flight vehicle to explore the airbreathing system-level potential of scramjets.

The military-oriented endothermically fueled, scramjet engine flight demonstrator (EFSEFD) was initiated in early 2003. At that time the first test flight was planned for late 2006. If successful, 5-11 flights could be performed, with as many as four more following over a roughly 18-month period, and the rest, 18 months after that. These test flights differ significantly from those of NASA's X-43C. In the latter, a three-flowpath scramjet module featuring variable-geometry inlets will be flown, with the flowpaths mounted in a side-by-side configuration. In contrast, the test vehicles used to explore scramjet military uses will each be powered by a single scramjet sporting a fixed-geometry inlet.

In January 2004 a team consisting of Pratt & Whitney (P&W) and Boeing Phantom Works was selected by the U.S. Air Force Research Laboratory (AFRL) to flight test the Endothermically Fueled Scramjet Engine Flight Demonstrator (EFSEFD), also known as the Scramjet Engine Demonstrator - WaveRider (SED-WR). The first year contract, which is valued at $7.7M (total program value was estimated at that time at approximately $140 million), was awarded to the team to explore the airbreathing system-level potential of scramjets through multiple flight tests that will begin in the 2007-2008 time frame.

The 26-ft.-long, 4,000-lb. stack that will be used in the single engine demonstration includes, from front to rear, a scramjet-powered free-flying vehicle incorporating a compression forebody, a transition section and a booster from an ATACMS missile. Each flight vehicle will consist of one Pratt & Whitney scramjet engine, based on technology developed under AFRL/PR's Hydrocarbon Scramjet Engine Technology (HySET) Program, integrated by Boeing into an expendable WaveRider configured air vehicle. During the flight demonstrations, a B-52 will carry the SED-WR vehicle to an altitude of about 35,000 ft and then release it. Initially propelled by an Army tactical missile system [ATACMS] solid rocket booster, the scramjet will take over at approximately Mach 4.5, and the vehicle will accelerate to a flight speed between Mach 6.0 and 7.0+. Applications for this propulsion concept include space access and fast-reaction military systems.

The use of an other transaction agreement on 09 September 2003 allowed two traditional defense contractors to form a consortium rather than having a prime/subcontractor relationship under the traditional FAR based contract. The Scramjet Engine Demonstrator-Wave Rider Consortium is comprised of Pratt & Whitney and Boeing, Advanced Space and Launch Systems. By forming the consortium, the Government will obtain significant additional prototype development effort by converting the customary indirect costs associated with a prime/subcontractor relationship into additional government funded direct costs. This also fosters an agile business partnering relationship between the consortium and the Government, who will utilize a team approach to enable the Government and consortium to be flexible in their program management decision making process.

The use of an other transaction agreement [OTA] resulted in the participation of non-traditional defense contractors which are as follows: (1) Ormond LLC, Kent, WA (providing intricate water-jet milling of heat exchanger patterns), (2) Dynamic Gunver Technologies LLC, Manchester, CT (providing laser welding of engine panels without impinging on heat exchanger patterns) (3) Jansen's Aircraft Systems Controls, Tempe, AZ (providing integration of valve sealing technologies with electronic controls at elevated temperatures and pressures), (4) Pioneer Aerospace, South Windsor, CT (providing the recovery system), (5) Starfire Systems, Malta, NY (providing the carbon/SiC nose and tail assembly), (6) Veridian Engineering, Buffalo, NY (providing wind tunnel testing), (7) Howmet Castings, Hillsboro, TX (providing vehicle body structural casting). Use of an OTA facilitates the use of subcontractors for fabrication of prototype hardware and/or services whose accounting and quality systems need not be subject to standard Government FAR/DFAR contract requirements.

The Propulsion Directorate's Scramjet Engine Demonstration (SED) Program, which started in December 2003, successfully completed a Preliminary Design Review (PDR) in December 2004. A follow-on contract was awarded on 7 January 2005 for the detailed design of a flight demonstrator using the Hypersonic Technology (HyTech) scramjet engine design. The SED-WaveRider Consortium contract, valued at approximately $70 million, will take the program through the detailed design phase culminating with a Critical Design Review (CDR) in January 2007.

A priced option was also negotiated, valued at approximately $60 million, to enable fabrication and flight test of the SED with a first flight scheduled for December 2008. The SED Program will acquire ground and in-flight test data of an operating, actively cooled, self-controlled prototype scramjet engine.

As of early 2006 it was planned that the Scramjet Engine Demonstrator-WaveRider program would execute multiple flight tests of the SED-WR vehicle in 2009. The technical objective of this effort is to flight test the United States Air Force (USAF) Hypersonic Technology (HyTech) scramjet engine, using endothermic hydrocarbon fuel. The goals of the program are (1) to acquire ground and in-flight test data of an operating, actively cooled, self-controlled prototype scramjet engine, (2) demonstrate the viability of the HyTech endothermically fueled engine in flight, and (3) prove the practicality of a free-flying scramjet powered vehicle.

Four X-51A cruisers have been built for the Air Force and the (Defense Advanced Research Projects Agency) by industry partners Pratt & Whitney Rocketdyne and Boeing. Air Force officials intend to fly the three remaining X-51A flight test vehicles in the fall of 2010. Air Force officials plan to fly each on virtually identical flight profiles, building knowledge from each successive flight.

An X-51A Waverider flight-test vehicle successfully made the longest supersonic combustion ramjet-powered hypersonic flight May 26 off the southern California Pacific coast. The more than 200 second burn by the X-51's Pratt & Whitney Rocketdyne-built air breathing scramjet engine accelerated the vehicle to Mach 6. The previous longest scramjet burn in a flight test was 12 seconds in a NASA X-43. Air Force officials called the test, the first of four planned, an unqualified success. The flight is considered the first use of a practical hydrocarbon fueled scramjet in flight.

Not everything went perfectly on the first flight test. The vehicle failed to accelerate as quickly as anticipated and the flight test had to be terminated after 143 seconds under scramjet power. A perfect flight would have lasted another 100 seconds and accelerated the X-51A cruiser to Mach 6. After the flight, members of the flight test team independently scoured over telemetry data for a month. Then they conducted a comprehensive "fault tree analysis" to identify every piece of anomalous data to determine the root cause. Two separate fault trees were identified: The vehicle failed to accelerate as rapidly as expected and unexpected temperatures and pressures were observed in internal sections of the cruiser. Engineers examined and walked through 156 different nodes in excruciating detail in search of a cause.

Program officials already knew from wind tunnel engine tests about the intense heat the scramjet engine and hypersonic flight creates. During flight, the scramjet engine actually grows about three-fourths of an inch. The effect complicates design for such things as interface seals. The Boeing "Phantom Works" and Pratt & Whitney Rocketdyne teams pulled the engines from the three remaining flight test vehicles and focused on the interface between the rear of the fuel-cooled engine and its vehicle mounted nozzle. The effort identified an "apparent thermal seal breach" at the interface which was not as tight as it needed to be. This caused some of the hot gases that should have provided thrust to leak into the rear of the cruiser.

A flight test scheduled for 14 August 2012 reportedly ended in failure according to a tweet from's Danger Room on 15 August 2012, which said that a fin problem had caused control of the aircraft to be lost before the main engine could even be started. No official press release from the US Air Force of DARPA on the results of the test or possible rescheduling of the test were available by the end of the day on 14 August 2012. At that time, it was estimated that $250-300 million had been spent on the X-51 program.

In a note sent to the media on 15 August 2012, the US Air Force said that the X-51A test flight had ended prematurely. While the X-51 vehicle had safely separated from the B-52 carrier aircraft and the rocket booster had fired as planned, after 16 seconds, a fault was identified with one of the cruiser control fins. Once the X-51 separated from the rocket booster, approximately 15 seconds later, the cruiser was not able to maintain control due to the faulty control fin and was lost. The control subsystem at fault had not experienced issues in the previous 2 test flights and program officials were to begin to explore the circumstances of the failure. Following the 14 August 2012, one of the 4 X-51A aircraft product up to that point remained, but it was unclear whether that vehicle would be tested in its existing configuration.

Flight Simulator X-51

In April 1997 Jim Goldman created a concept aircraft for Flight Simulator, which he called the X-51. It was intended to obtain flight speeds up to MACH 3, with sustained speeds of MACH 1.8 to 2.3. This is an entirely fictitious aircraft, and should not be confused with an actual X-Plane.

 Flight Simulator X-51

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