November 28, 2007 In a landmark demonstration, Boeing and the U.S. Air Force have used "active flow control" technology to deploy munitions from a weapons bay at twice the speed of sound. The MK-82 Joint Direct Attack Munition Standard Test Vehicle was released from a rocket sled at the High-Speed Test Track at Holloman Air Force Base, New Mexico, representing the first safe release of munitions from a weapons bay at high supersonic speeds.
Active flow control technology involves placing a tandem array of microjets upstream of the weapons bay, which reduces the unsteady pressures inside the bay and modifies the flow outside to ensure the test vehicle travels out of the rocket sled correctly. "Active flow control technology will enable safe separation of weapons from weapons bays of future high speed aircraft," said Jim Grove, AFRL program manager for High Frequency Excitation Active Flow Control for Supersonic Weapon Release, or HIFEX. "This program also demonstrates that sled testing can provide a lower risk technology evaluation alternative to flight testing in this complex, high risk environment."
Wind tunnel testing indicated that without active flow control, the JDAM test vehicle would have returned to the bay. The release of the test vehicle from the rocket sled bay was a bigger challenge than an equivalent release from an aircraft bay at altitude, due to the reduced dynamic pressure, reduced vibration and increased amount of time in which to release a store enjoyed by the latter.
The sled used in the HIFEX test was designed by the U. S. Air Force 846th Test Squadron and the Support Systems unit of Boeing Integrated Defense Systems. At 65 700 pounds, it was 26 000 pounds heavier than any sled tested in more than ten years, but was faster by 400 feet per second. In the 57 year history of the Holloman High-Speed Test Track, it was the heaviest sled train to reach Mach 2. Powered by two pusher sleds, the HIFEX sled achieved thrusts of 438 000 pounds for 5.9 seconds on the first stage, 575 000 pounds for three seconds on the second stage, and 115 000 pounds for about 3.6 seconds on the third stage. The JDAM test vehicle was dispensed during peak velocity, which was about 2 000 feet per second. The sled train accelerated to more than 13 g's to get to peak velocity, and then decelerated at 7.5 g's for more than one mile to stop.
The HIFEX program began in 2001 under the Defense Advanced Research Projects Agency Tactical Technology Office which, together with Boeing, conducted eight wind tunnel tests to develop the active flow control concept and preliminary testing of the full-scale rocket sled demonstrator. In January 2007, DARPA transferred the HIFEX program to AFRL. AFRL is currently collaborating with the Aeronautical Systems Center to fund full-scale validation testing of the HIFEX concept in order to demonstrate that active flow control is capable of outperforming the passive control of a weapons bay spoiler.
Boeing, the U.S. Air Force 846th Test Squadron, Waveflows, and EPIC Systems will conduct additional testing of the full-scale HIFEX system in 2008. AFRL intends to use active flow control technology from HIFEX to develop full-envelope weapon release systems for future U.S. Air Force Global Strike aircraft.
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