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Transonic test leads rekindled NASA supersonic transport aircraft effort

NASA engineers and technicians are close to completing the initial round of testing on a 1/15 semi-span scale supersonic transport model in Langley Research Center's transonic windtunnel.

The work is part of a rekindled five-year $275 million supersonic research programme that NASA set in motion this year, part of the broader fundamental aeronautics effort to spur foundational research in subsonic fixed-wing and rotary-wing vehicles as well as supersonic and hypersonic aircraft. Overall funding for the four areas this year and for the next four years is roughly $750 million.

The ultimate goal of the new supersonic research programme is not to build a demonstrator, but to develop the tools and technologies that could allow the aviation industry to design and build a 50- to 100-seat supersonic transport aircraft by 2018, says Peter Coen, NASA's principal investigator for supersonic fundamental aeronautics.

As such, Coen has projects under way in 10 key areas, including cruise efficiency for airframes and propulsion, lightweight durable engines and airframes, sonic boom modelling, high-altitude emissions and aero propulso-servo-elasticity (APSE).

The work is being done by NASA, industry or academia through partnerships and competitive research grants.

APSE windtunnel tests finishing up this week at Langley are designed to determine the aeroelastic response of the 1/15 scale model to control inputs from controllable wing flaps, canard and stabilator, says Walt Silva, NASA senior research scientist and associate principal investigator for APSE.

Silva has been running "open loop" transonic tests since mid-May in the tunnel, which can run as fast as Mach 1.2. During the tests, which will end this week, engineers command fixed inputs to the control actuators and measure the aircraft's response with accelerometers, high accuracy video cameras and other devices.

Once the responses are correlated with the simulated results of computational fluid dynamics (CFD) and structural modelling programmes for the same conditions later this year, the test-verified models will then be used to develop closed-loop control laws for gust alleviation and flutter suppression that will be tested on the semi-span model in the windtunnel next year.

Additionally, Silva is investigating the effects of the flexible wings on engine performance in terms of air flow. The model includes two simulated engines under the wing.

With an understanding of the aeroelastic properties and the ability to incorporate flutter and gust control, NASA says manufacturers will be able to design lighter wings.

Originally developed for NASA's High Speed Research (HSR) programme - a $1.5 billion effort with Boeing and McDonnell Douglas that was cancelled in 1999 after the two companies merged - the million-dollar model is structurally representative of the full-scale aircraft with respect to at least the first 10 resonance modes, says Silva. The model's wings are built from glassfibre while the longitudinal internal structure is made from carbonfibre.

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