X-51 & Falcon HTV-2 tests very near....
Hypersonic proponents worldwide will eagerly watch two long-awaited technology demonstrations starting with the imminent first flight attempt for the X-51 Waverider, to be followed within a month by the first flight of the Falcon HTV-2 hypersonic test vehicle.
Successful flights for both are seen as critical to proving the practicality of hypersonic technology for high-speed weapon, reconnaissance and space-access applications. The X-51 is a Mach 6+vehicle powered by a hydrocarbon fuel-cooled scramjet, and
could perform the longest duration air-breathing hypersonic flight in history. The HTV-2 is an unpowered hypersonic glider aimed at gathering rare performance data.
Researchers say success in at least one of the four planned X-51 flights, the first of which could come as soon as Mar. 18, will reinforce the case for follow-on development. The HTV-2 will be boosted on a Minotaur IV Lite from Vandenberg AFB, Calif., to an impact near the Reagan Test Site at Kwajalein Atoll in the Marshall Islands. A launch is planned within an 8-day window—Apr. 20-27.
Preparations for the first flight of the X-51, a joint effort involving the Air Force, Whitney Rocketdyne and Boeing, are now complete, says Boeing X-51 program manager Joe Vogel. “The vehicle is ready to go and we’re ready to make it happen.” Originally expected to fly in late October 2009, the test has slipped mainly because of availability of the B-52H carrier aircraft that will launch the X-51 over the Pacific.
Two captive-carry tests were flown in December and January, the second of which “threaded the eye of the storm” through successive weather fronts to fly out over the Point Mugu, Calif.-controlled test range, from which the X-51 will be launched at 50,000 ft. “
We can’t fly on a rainy day,” adds Vogel. That is not because of weather; it is done to control test parameters.
Two test vehicles are complete with “just close-out work to do,” Vogel says. The remaining pair, which may have updated guidance software to test possible hypersonic navigation, will be ready “in the next couple of months. We’ve got a lot of confidence it’s going to work as we hope it will,” he adds.
The flight of the Lockheed Martin-built HTV-2 is the first of two planned from Vandenberg. April’s flight, originally due in May 2009, will be followed by a second later this year to evaluate cross-range maneuvering capability and the thermal protection system. The ability of the GPS/INS-guided navigation system to acquire signals through plasma will also be vetted.
The HTV-2 program will be the first beneficiary of an upgrade to the Air Force’s Hypervelocity Wind Tunnel 9 in White Oak, Md. Following a 14-month refurbishment to install a new control system and instrumentation, an HTV-2 model is being used for initial runs of the facility, capable of conducting aerodynamic and aerothermal tests
at speeds up to Mach 14.
“Instead of using the traditional 7-deg. cone, we chose the HTV because the complexity of its 3D geometry drives the physics and provides the perfect testbed for us to look at hard problems,” says Dan Marren, director of the White Oak site, which is part of the USAF’s Arnold Engineering Development Center. “After they fly, they’ll come back here to understand what they see in flight.”
Refurbishment has upgraded the facility to a fully digital control system for increased test accuracy, but the biggest change is a new suite of advanced instrumentation that enables the tunnel to be used to investigate the physics of hypersonic flight. Marren says Tunnel 9 had been used mainly to test systems close to being fielded, such as the Theater High-Altitude Area Defense interceptor.
The facility is the highest-pressure wind tunnel in the world, he says, operating at
up to 30,000 psi. and temperatures up to 3,500F. The 5-ft.-dia. test cell uses electrically heated nitrogen as the working fluid. Unlike hypersonic shock tunnels, which only run for milliseconds, Tunnel 9 can run at Mach 14 for 1 sec. at high pressures and 15 sec. at low, allowing the model to be moved during a run, changing angle of attack, for example.
The tunnel can replicate the boundary-layer physics of hypersonic vehicles, enabling investigation of the transition between laminar and turbulent flow and the resulting increased heating. The new instrumentation will be key in these investigations.
Special paint on the model is viewed via thermal imager to determine surface temperatures. The HTV-2 tests will be the first time this is used on a model that changes pitch during a run, Marren says. New sensors measure both pressures and frequencies to determine the state of the boundary layer, while focused Schlieren imaging is correlated with the pressure measurements to look closely at the boundary layer and see what is causing the transition to turbulent flow.
Data from the first run of the refurbished Tunnel 9, on Mar. 4, were “outstanding,” says Marren.
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