X-51A Scramjet Engine Completes Ground Tests
[2008-12-23 17:03:34]
X-51A Scramjet Engine Completes Ground Tests
By Graham Warwick
A year from now, over the Pacific Ocean off California in airspacecleared of all civilian traffic, hypersonics could take a stepcloser to reality. In the same skies where five years earlier theX-43A Hyper-X flew for 10 sec. at Mach 9.6, powered by asupersonic-combustion ramjet, the X-51A WaveRider is planned to flyon scramjet power for 5 min., accelerating from Mach 4.7 to beyondMach 6 and demonstrating that sustained hypersonic flight ispractical.
Burning hydrogen in a heavy copper engine that simply soaked up theheat of supersonic combustion and began melting within seconds, theX-43A showed scramjet-powered flight was feasible. The X-51A willhave a flightweight engine, cooled by its own hydrocarbon fuel anddesigned to run for as long as there is JP-7 in the tanks.
Boeing's X-51A and its Pratt & Whitney Rocketdyne (PWR)scramjet can trace their roots back 20 years to the X-30 NationalAeroSpace Plane, an overambitious and unsuccessful attempt to builda Mach 30 single-stage-to-orbit technology demonstrator. TheX-51A's goals are far more modest, but it could lead directly todevelopment of a hypersonic long-range strike missile. It wouldalso be a step closer to an eventual air-breathing space accessvehicle.
"The X-51A will demonstrate the technology is ready for applicationin a program," says Charles Brink, Air Force Research Laboratoryprogram manager. AFRL is funding three-quarters of the $246-millioncontract, with the balance being provided by the U.S. DefenseAdvanced Research Projects Agency.
PWR has just completed ground runs of the flight clearance enginein the high-temperature tunnel at NASA Langley Research Center,making sure the scramjet will start when the X-51A separates fromits modified missile booster, even if the Mach number and dynamicpressure (Q) are not quite as planned. Designated the SJX61-2 andknown simply as "X-2," the engine completed eight runs at Mach 4.6and 11 at Mach 5, for a total of 11.4 min., about twice theexpected flight time.
The tests cleared the "start box" for the scramjet, showing marginto handle off-design conditions. "There was repeatable, fairlyrobust light-off throughout the envelope," says Brink. "We testedoff-nominal - high-Q, low-Q, varied angles of attack, coldethylene, hot ethylene - and saw very reliable light-off."
Easily ignited ethylene is used to start combustion and beginheating the hydrocarbon fuel so it will burn more readily wheninjected into the supersonic flow. X-2 was the first engine to betested with the flight ethylene bottle and fuel pump planned forthe X-51A.
"We found some 'ohs' about the software," says Brink. When testingat above-nominal dynamic pressure and engine airflow, the controlsystem commanded a fuel/air ratio higher than allowed by thesoftware and the engine shut down in mid-test. "I'm glad we testedoff-condition. That might have bit us in flight," he says.
X-2's operability and performance met expectations. "It matched ourpredictions," says Curtis Berger, PWR's hypersonics programsdirector. "But our models are becoming pretty mature. This is ourfourth flightweight fuel-cooled scramjet through freejet testing."The four engines between them logged 161 test runs since 2003, atspeeds from Mach 4.5 to 6.5.
Last year, in the same NASA tunnel, the X-51A ground demonstratorengine, SJX61-1, completed 58 runs and 17.8 min. of combustion. "Wehad four risks left tied to X-2: mapping the start box, showingmargin on the box, and the flight fuel pump and ethylene tank,"says Berger. "They're burned down to green. We feel good aboutgoing to flight."
Vibration caused by the acoustic environment in the combustor wasnoticed in earlier scramjets and confirmed in X-1, says Berger,adding, "We designed for it in X-2." Where components mount to theengine and the engine attaches to the cruiser, isolators have beendesigned in. "The acoustic vibration levels are substantial, butnothing we couldn't design for. We understand it, have mitigated itand for the next system we have models to predict it."
Engines for all four X-51As will be delivered to Boeing by earlyNovember. The first of these, designated SJY61-4, will be mountedon the Boeing-built cruiser vehicle. This will then be attached toits modified Atacms missile booster and the complete stack, calledthe static test vehicle (STV), will go through ground vibration andstructural modes testing. The STV will be refurbished to become thefourth flight vehicle.
For PWR, X-2 was the latest in a series of dual-moderamjet/scramjets dating back to the performance test engine run in2001 under the HySET program started by AFRL after cancellation ofthe X-30. The first flightweight ground demonstrator engine (GDE 1)ran in 2003 and had an open-loop fuel system. One stream of JP-7cooled the engine structure; a second was heated and injected intothe scramjet.
As a follow-on to the X-43A, AFRL and NASA had planned to build thelarger X-43C, powered by three scramjets burning storablehydrocarbon fuel. The first engine was 95% built when NASA canceledthe program in 2004, but the scramjet was completed andground-tested as the GDE-2. "This was the first Air Force scramjettested at NASA, and the first time we closed the loop on thethermal system," says Brink.
Achieving thermal balance with a closed-loop fuel system is a keyto making scramjets practical. Using the fuel to cool the structureallows the engine to be made of Inconel 625 nickel-based alloyrather than more-exotic high-temperature materials. At the sametime, the heat absorbed by the fuel "cracks" the high-flashpointJP-7 into lighter hydrocarbons that burn more readily when injectedinto the supersonic flow.
In the X-51A, fuel flows through channels inside the walls of thescramjet. As the fuel moves from front to back through the engine,heat combines with a catalytic coating on the heat-exchanger panelsto break down the JP-7, which is then brought forward to hot-gasdistribution valves that spray the vaporized fuel into thecombustion chamber.
Thermal equilibrium must be maintained as the vehicle accelerates."The system has to maintain enough flow through the structure tokeep it cool, put enough heat into the fuel so it burns, and notrecirculate or dump fuel," says Berger. "It's balancing the fuelflow so it keeps cool enough, gets hot enough and produces maximumthrust at various Mach numbers. How that is all done is what weknow."
Where the fuel is injected is another critical aspect of making ascramjet practical. In the supersonic flow, air and fuel must mixand burn in milliseconds. Injecting fuel at the front of the enginegives more time, but risks "unstarting" the inlet as backpressurefrom combustion blows the shockwave system out of the duct. Theseshocks on the forebody and inlet compress the air entering theengine. "We want to burn the fuel as close to the inlet as we can,but we can unstart the engine and disgorge the shock," says NASA'sKen Rock.
Therefore, fuel is first injected toward the rear of the enginethen staged forward as the vehicle accelerates and dynamic pressureincreases, making it harder to unstart the inlet. "At lower Mach werelease the heat further aft, and at higher Mach we inject fuelfurther forward to get increased performance as the vehicleaccelerates," Rock says.
While the X2 engine tests were under way, Boeing was beginningassembly of the first X-51As. The 168-in.-longmissile-representative cruiser vehicle is built from conventionalmaterials such as aluminum and titanium. A tungsten nose, compositeleading edges and lightweight ablator on the skin and in the nozzleprovide thermal protection. With its modified Atacms booster andflow-through interstage, the complete stack as carried aloft by theB-52 mothership will be 301-in. long.
Flight operations will begin at NASA Dryden Flight Research Centeron Edwards AFB, Calif., in February next year. The first X-51A isexpected to arrive by July to begin ground compatibility tests withthe B-52. The first captive flight is planned for August over theEdwards range to vet communications and telemetry links. A dressrehearsal over the Pacific using P-3s to record and relay telemetryis planned for September.
All four flights slated for early October 2009 through lateFebruary 2010 will share one goal, "to light off and acceleratethrough as many Mach numbers as we can," says Brink. "Realisticallyif we get two flights out of four we'll be happy. Look at thestatistics. Things will go wrong." Flights 3 and 4 will carryspecialized software for NASA Langley to measure vehicleaerodynamic parameters in flight.
After takeoff from Edwards, the B-52 will climb to almost 50,000ft. and release the stack. The booster will burn for almost 30 sec.and accelerate to Mach 4.6-4.8. During the boost, air will flowthrough the cruiser's engine, exiting via the interstage, to startthe inlet and begin warming the scramjet and its circulating fuel.
After booster burnout and separation, the vehicle will coast for acouple of seconds, then ethylene will be injected to light off theengine. Heated by the burning ethylene, fuel will be introduced andthe two flows combusted simultaneously until thermal equilibrium isachieved and the vehicle can accelerate on JP-7 alone. Thermalbalance occurs within seconds, says Berger. "Then it will only stopflying when it runs out of fuel."
For the X-51A that will mean about 300 sec. of powered flightfollowed by 500 sec. of unpowered descent to a watery end in thePacific. "Boeing is exploring a recovery system if we go ahead withfurther vehicles," says Brink. "We can do away with someinstrumentation and miniaturize components to make room."
Boeing, meanwhile, has schemed variants of the X-51 "from B throughH," says program manager Joe Vogel. The proposed X-51B would bepowered by an Alliant Techsystems thermally throated ramjet, asimplified subsonic-combustion engine designed to maintain a Mach 5cruise.
Using "minimal funds" added by Congress, Boeing has completed a"fairly detailed" installation study on the X-51B, and ATK is aboutto begin ground tests of the engine, says Brink, but there is noAir Force funding for the vehicle. For now the focus is on theX-51A, and on being able to correlate ground and flight tests of afuel-cooled scramjet. "We are on the path to practicalhypersonics," says Berger.
http://www.aviationweek.com/avnow/news/channel_awst_story.jsp?id=news/aw110308p1.xml&source=rss [2008-11-4]
Tag : copper alloyBy Graham Warwick
A year from now, over the Pacific Ocean off California in airspacecleared of all civilian traffic, hypersonics could take a stepcloser to reality. In the same skies where five years earlier theX-43A Hyper-X flew for 10 sec. at Mach 9.6, powered by asupersonic-combustion ramjet, the X-51A WaveRider is planned to flyon scramjet power for 5 min., accelerating from Mach 4.7 to beyondMach 6 and demonstrating that sustained hypersonic flight ispractical.
Burning hydrogen in a heavy copper engine that simply soaked up theheat of supersonic combustion and began melting within seconds, theX-43A showed scramjet-powered flight was feasible. The X-51A willhave a flightweight engine, cooled by its own hydrocarbon fuel anddesigned to run for as long as there is JP-7 in the tanks.
Boeing's X-51A and its Pratt & Whitney Rocketdyne (PWR)scramjet can trace their roots back 20 years to the X-30 NationalAeroSpace Plane, an overambitious and unsuccessful attempt to builda Mach 30 single-stage-to-orbit technology demonstrator. TheX-51A's goals are far more modest, but it could lead directly todevelopment of a hypersonic long-range strike missile. It wouldalso be a step closer to an eventual air-breathing space accessvehicle.
"The X-51A will demonstrate the technology is ready for applicationin a program," says Charles Brink, Air Force Research Laboratoryprogram manager. AFRL is funding three-quarters of the $246-millioncontract, with the balance being provided by the U.S. DefenseAdvanced Research Projects Agency.
PWR has just completed ground runs of the flight clearance enginein the high-temperature tunnel at NASA Langley Research Center,making sure the scramjet will start when the X-51A separates fromits modified missile booster, even if the Mach number and dynamicpressure (Q) are not quite as planned. Designated the SJX61-2 andknown simply as "X-2," the engine completed eight runs at Mach 4.6and 11 at Mach 5, for a total of 11.4 min., about twice theexpected flight time.
The tests cleared the "start box" for the scramjet, showing marginto handle off-design conditions. "There was repeatable, fairlyrobust light-off throughout the envelope," says Brink. "We testedoff-nominal - high-Q, low-Q, varied angles of attack, coldethylene, hot ethylene - and saw very reliable light-off."
Easily ignited ethylene is used to start combustion and beginheating the hydrocarbon fuel so it will burn more readily wheninjected into the supersonic flow. X-2 was the first engine to betested with the flight ethylene bottle and fuel pump planned forthe X-51A.
"We found some 'ohs' about the software," says Brink. When testingat above-nominal dynamic pressure and engine airflow, the controlsystem commanded a fuel/air ratio higher than allowed by thesoftware and the engine shut down in mid-test. "I'm glad we testedoff-condition. That might have bit us in flight," he says.
X-2's operability and performance met expectations. "It matched ourpredictions," says Curtis Berger, PWR's hypersonics programsdirector. "But our models are becoming pretty mature. This is ourfourth flightweight fuel-cooled scramjet through freejet testing."The four engines between them logged 161 test runs since 2003, atspeeds from Mach 4.5 to 6.5.
Last year, in the same NASA tunnel, the X-51A ground demonstratorengine, SJX61-1, completed 58 runs and 17.8 min. of combustion. "Wehad four risks left tied to X-2: mapping the start box, showingmargin on the box, and the flight fuel pump and ethylene tank,"says Berger. "They're burned down to green. We feel good aboutgoing to flight."
Vibration caused by the acoustic environment in the combustor wasnoticed in earlier scramjets and confirmed in X-1, says Berger,adding, "We designed for it in X-2." Where components mount to theengine and the engine attaches to the cruiser, isolators have beendesigned in. "The acoustic vibration levels are substantial, butnothing we couldn't design for. We understand it, have mitigated itand for the next system we have models to predict it."
Engines for all four X-51As will be delivered to Boeing by earlyNovember. The first of these, designated SJY61-4, will be mountedon the Boeing-built cruiser vehicle. This will then be attached toits modified Atacms missile booster and the complete stack, calledthe static test vehicle (STV), will go through ground vibration andstructural modes testing. The STV will be refurbished to become thefourth flight vehicle.
For PWR, X-2 was the latest in a series of dual-moderamjet/scramjets dating back to the performance test engine run in2001 under the HySET program started by AFRL after cancellation ofthe X-30. The first flightweight ground demonstrator engine (GDE 1)ran in 2003 and had an open-loop fuel system. One stream of JP-7cooled the engine structure; a second was heated and injected intothe scramjet.
As a follow-on to the X-43A, AFRL and NASA had planned to build thelarger X-43C, powered by three scramjets burning storablehydrocarbon fuel. The first engine was 95% built when NASA canceledthe program in 2004, but the scramjet was completed andground-tested as the GDE-2. "This was the first Air Force scramjettested at NASA, and the first time we closed the loop on thethermal system," says Brink.
Achieving thermal balance with a closed-loop fuel system is a keyto making scramjets practical. Using the fuel to cool the structureallows the engine to be made of Inconel 625 nickel-based alloyrather than more-exotic high-temperature materials. At the sametime, the heat absorbed by the fuel "cracks" the high-flashpointJP-7 into lighter hydrocarbons that burn more readily when injectedinto the supersonic flow.
In the X-51A, fuel flows through channels inside the walls of thescramjet. As the fuel moves from front to back through the engine,heat combines with a catalytic coating on the heat-exchanger panelsto break down the JP-7, which is then brought forward to hot-gasdistribution valves that spray the vaporized fuel into thecombustion chamber.
Thermal equilibrium must be maintained as the vehicle accelerates."The system has to maintain enough flow through the structure tokeep it cool, put enough heat into the fuel so it burns, and notrecirculate or dump fuel," says Berger. "It's balancing the fuelflow so it keeps cool enough, gets hot enough and produces maximumthrust at various Mach numbers. How that is all done is what weknow."
Where the fuel is injected is another critical aspect of making ascramjet practical. In the supersonic flow, air and fuel must mixand burn in milliseconds. Injecting fuel at the front of the enginegives more time, but risks "unstarting" the inlet as backpressurefrom combustion blows the shockwave system out of the duct. Theseshocks on the forebody and inlet compress the air entering theengine. "We want to burn the fuel as close to the inlet as we can,but we can unstart the engine and disgorge the shock," says NASA'sKen Rock.
Therefore, fuel is first injected toward the rear of the enginethen staged forward as the vehicle accelerates and dynamic pressureincreases, making it harder to unstart the inlet. "At lower Mach werelease the heat further aft, and at higher Mach we inject fuelfurther forward to get increased performance as the vehicleaccelerates," Rock says.
While the X2 engine tests were under way, Boeing was beginningassembly of the first X-51As. The 168-in.-longmissile-representative cruiser vehicle is built from conventionalmaterials such as aluminum and titanium. A tungsten nose, compositeleading edges and lightweight ablator on the skin and in the nozzleprovide thermal protection. With its modified Atacms booster andflow-through interstage, the complete stack as carried aloft by theB-52 mothership will be 301-in. long.
Flight operations will begin at NASA Dryden Flight Research Centeron Edwards AFB, Calif., in February next year. The first X-51A isexpected to arrive by July to begin ground compatibility tests withthe B-52. The first captive flight is planned for August over theEdwards range to vet communications and telemetry links. A dressrehearsal over the Pacific using P-3s to record and relay telemetryis planned for September.
All four flights slated for early October 2009 through lateFebruary 2010 will share one goal, "to light off and acceleratethrough as many Mach numbers as we can," says Brink. "Realisticallyif we get two flights out of four we'll be happy. Look at thestatistics. Things will go wrong." Flights 3 and 4 will carryspecialized software for NASA Langley to measure vehicleaerodynamic parameters in flight.
After takeoff from Edwards, the B-52 will climb to almost 50,000ft. and release the stack. The booster will burn for almost 30 sec.and accelerate to Mach 4.6-4.8. During the boost, air will flowthrough the cruiser's engine, exiting via the interstage, to startthe inlet and begin warming the scramjet and its circulating fuel.
After booster burnout and separation, the vehicle will coast for acouple of seconds, then ethylene will be injected to light off theengine. Heated by the burning ethylene, fuel will be introduced andthe two flows combusted simultaneously until thermal equilibrium isachieved and the vehicle can accelerate on JP-7 alone. Thermalbalance occurs within seconds, says Berger. "Then it will only stopflying when it runs out of fuel."
For the X-51A that will mean about 300 sec. of powered flightfollowed by 500 sec. of unpowered descent to a watery end in thePacific. "Boeing is exploring a recovery system if we go ahead withfurther vehicles," says Brink. "We can do away with someinstrumentation and miniaturize components to make room."
Boeing, meanwhile, has schemed variants of the X-51 "from B throughH," says program manager Joe Vogel. The proposed X-51B would bepowered by an Alliant Techsystems thermally throated ramjet, asimplified subsonic-combustion engine designed to maintain a Mach 5cruise.
Using "minimal funds" added by Congress, Boeing has completed a"fairly detailed" installation study on the X-51B, and ATK is aboutto begin ground tests of the engine, says Brink, but there is noAir Force funding for the vehicle. For now the focus is on theX-51A, and on being able to correlate ground and flight tests of afuel-cooled scramjet. "We are on the path to practicalhypersonics," says Berger.
Source: 沱沱网
Keywords:Industrial Supplies
Related Articles:
