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Using the Tu-144LL to conduct flight experiments allowed researchers to compare full-scale supersonic aircraft flight data with results from models in wind tunnels, computer-aided techniques and other flight tests. The flight experiments provided unique aerodynamic, structures, acoustics and operating environment data on supersonic passenger aircraft.
Six flight and two ground experiments were conducted during the program's first flight phase, which began in June, 1996 and concluded in February, 1998 after 19 research flights. A shorter follow-on program involving about seven flights began in September, 1998 and concluded in April, 1999. All flights were conducted in Russia from Tupolev's facility at the Zhukovsky Air Development Center near Moscow.
The Tu-144LL supersonic research program was conducted as part of NASA's High Speed Research (HSR) program, managed by NASA Langley Research Center, Hampton, Va. The Tu-144LL project established direct working relationships between American and Russian aircraft manufacturers and enhanced the relationship between U.S. and Russian aeronautical agencies.
The project was enabled by an agreement signed in June 1994 by U.S. Vice President Al Gore Jr. and Russian Prime Minister Viktor Chernomyrdin. The Langley Research Center subsequently contracted with the Boeing Commercial Airplane Group which in turn contracted with the Russian aerospace firm for use of the modified Tu-144D jetliner to conduct the flight experiments. In addition to Boeing, the American industry team for the Tu-144LL project included engine manufacturers Pratt & Whitney and General Electric. NASA's Dryden Flight Research Center, Edwards, Calif., provided instrumentation and data processing support as well as management of the actual flight test project. IBP, Ltd., London, UK, assisted with contract management.
The aircraft flown in NASA's research program was a "D" model and was the last Tu-144 built. Bearing tail number 77114, it was constructed in 1981 and had logged a total flight time of only 82 hours and 40 minutes, most of that for research and test purposes, before being selected for the NASA-sponsored program. It was never used in commercial service.
The aircraft underwent many upgrades and modifications in its conversion to the "LL" Flying Laboratory, including the installation of more powerful NK-321 augmented-turbofan engines that were originally produced for the Tupolev Tu-160 Blackjack bomber.
A new Damien digital data collection system replaced an earlier analog system to collect airworthiness data and data from the experiments. Thermocouples, pressure sensors, microphones and skin friction gauges were placed on the Tu-144LL to measure the aerodynamic boundary layer - the layer where the air interacts with the surfaces of a moving aircraft. It also carried a significant number of other research instruments. An emergency crew escape system was also installed.
Out of 50 experiments originally proposed, project officials selected eight, including six flight and two ground engine experiments, for the first phase of flight research. The flight experiments included studies on the aircraft's exterior surface, internal structure and engine temperatures, boundary layer airflow, the wing's ground effect characteristics, interior and exterior noise, handling qualities in various flight profiles, and in-flight structural flexibility. The two ground experiments, completed before the flight experiments began, studied the effect of air inlet structures on the airflow entering the engine and the effect on engine performance when supersonic shock waves rapidly change position in the engine air inlet.
The second phase of research flights entailed further study of the six flight experiments conducted during the first series. Additional instrumentation was installed by Tupolev technicians to assist in acquisition and analysis of data. A new experiment aimed at measurement of in-flight deflections of the wing and fuselage was conducted, and American-supplied transducers and sensors were installed to measure nose boom pressures, angle-of-attack and sideslip angles with greater accuracy. In addition, two NASA research pilots - Robert Rivers of NASA Langley and Gordon Fullerton of NASA Dryden - assessed the Tu-144LL's handling qualities at subsonic and supersonic speeds during the first three flights in September, 1998. The follow-on series concluded after four data-collection flights in the spring of 1999.