Aerospace Technology Development

SR-71 Research Flights End

AFOUR-FLIGHT-TEST SERIES FOR 1999 WAS completed in September with a 41-foot-long test fixture mounted atop the aft section of the SR-71 "Blackbird" research aircraft. The flight series evaluated the SR-71's performance, handling and flying qualities and proved that the SR-71 is a viable testbed for future technologies that need a high-speed, high-altitude flight environment, although the two-hour flight did not reach Mach 3.2.

Unlike wind tunnels that are constrained by its walls, the SR-71 airplane flies in actual atmospheric conditions, such as moisture and temperatures, and at extreme altitudes and speeds, making it an ideal testbed for supersonic flight. "It flew like a scalded cat," said SR-71 Flight Test Engineer Marta Bohn-Meyer of the SR-71 during its final test flight of the year. She said the plane was unbelievable in how it pushed to go faster.

The SR-71 stopped short of one test point above Mach 3 because of a failed liquid nitrogen system used for the test fixture to purge. This purge system, proven effective in past flights, was to address concerns of overheating the fixture's internal systems, said Tim Moes, Dryden Flight Research Center's chief engineer for these research flights. The failure is well understood and will be instituted to prevent future failure.

The mounted test fixture was originally used for the Linear Aerospike SR-71 Experiment (LASRE) that supported research for the X-33 program. During this recent series of flight tests, the fixture showed barely any impact on the SR-71A's stability, handling and flying characteristics while soaring at Mach 3, three times the speed of sound.

The SR-71 can fly more than 2,200 miles per hour at Mach 3 and at altitudes above 85,000 feet. Two SR-71s were first loaned to NASA from the U.S. Air Force, and an ownership transfer to NASA followed. Since then, two additional flyable SR-71s were turned over to NASA. The SR-71A model was used for the four-flight-test series. NASA's "B" model, used for proficiency training for pilots and flight test engineers, recently completed its planned 200-hour phase inspection and has been put into flyable storage.

As research platforms, the SR-71s carry out research and experiments in a variety of areas: aerodynamics, propulsion, structures, thermal protection materials, high-speed and high-temperature instrumentation, atmospheric studies and sonic boom characteristics. SR-71 flights have provided information on the presence of atmospheric particles at extremely high altitudes, where future hypersonic aircraft will be operating. Data from the SR-71's high-speed research program will be used to aid designers of future supersonic and hypersonic aircraft and propulsion systems. The SR-71 has also acted as a surrogate satellite for transmitters and receivers on the ground, assisting in the development of a commercial satellite-based—instant and wireless—personal communications network called IRIDIUM.

Another SR-71 project joined NASA and the University of California at Los Angeles (UCLA) to investigate the use of charged chlorine atoms to protect and rebuild the ozone layer. Ongoing research in high-speed, high-altitude flight continues to gain interest among the scientific community, industry and other government agencies. In future flight research programs, the four SR-71s will provide unsurpassed flexibility as well as additional capabilities to perform multiple high-speed research experiments.

For more information, contact Steven Schmidt at Dryden Flight Research Center. Call: 661/258-3395,
E-mail: steve.schmidt@mail.dfrc.nasa.gov Please mention you read about it in Innovation.