Jan. 22, 2009

Beth Dickey
Headquarters, Washington
202-358-2087
beth.dickey-1{at}nasa.gov

Gray Creech
Dryden Flight Research Center, Edwards, Calif.
661-276-2662
gray.creech{at}nasa.gov

RELEASE: 09-016

LANCETS FLIGHTS PROBE SUPERSONIC SHOCKWAVES

EDWARDS, Calif. -- NASA is concluding a series of flight tests to
measure shock waves generated by an F-15 jet in an effort to validate
computer models that could be used in designing quieter supersonic
aircraft.

The Lift and Nozzle Change Effects on Tail Shock, or Lancets, project
embodies research aimed at enabling the development of commercial
aircraft that can fly faster than the speed of sound without
generating annoying sonic booms over land. Supersonic flight over
land generally is prohibited because of annoyances caused by their
noise.

A sonic boom is created by shock waves that form on the front and
rear
of an aircraft. The boom loudness is related to the strength of the
shock waves. The formation of the shock waves is dependent on the
aircraft geometry and the way in which the wing generates lift.
During the flight tests at NASA's Dryden Flight Research Center in
Edwards, Calif., one of two F-15s generally followed 100 feet to 500
feet below and behind the other, measuring the strength of the
leading aircraft's shock waves at various distances using special
instruments. Global Positioning System relative positioning was used
to guide the pilot of the probing aircraft to a test position and for
accurate reporting of measurement locations.

Lancets is the latest in a series of NASA projects investigating the
effects of aircraft geometry and lift on the strength of shock waves.

NASA previously teamed with private companies to study the effect of
aircraft shape on the strength of shock waves and whether adding a
nose spike to an aircraft affects the strength of its shock waves in
order to validate design tools for aircraft fore-bodies.
A NASA F-15B was used as the test aircraft for the flights. It was
ideally suited for Lancets because its canards and engine nozzles can
be adjusted in flight.

Canards are small airfoils in front of the wing that are designed to
increase the aircraft's performance. Adjusting the canards changes
the lift of the main wing, which varies how much wing lift
contributes to the strength of the shock waves. This cannot be done
on a conventional aircraft without making expensive modifications to
the wing. Adjusting the engine nozzles alters the exhaust plumes from
the engines, which varies how much the rear of the aircraft
contributes to the strength of the shock waves.

A second NASA F-15B was the probing aircraft. It was fitted with a
special nose spike for taking shock strength measurements.
The flight results will be used by computational fluid dynamics
researchers at NASA's Langley Research Center in Hampton, Va.; NASA's
Ames Research Center at Moffett Field, Calif.; and at Dryden to
develop and validate improved tools that incorporate aft-shockwave
effects in the prediction of sonic booms. The flight data also will
be made available to interested university and industry partners in
order to further their research objectives.

The research is funded and managed by the Fundamental Aeronautics
Program, part of NASA's Aeronautics Research Mission Directorate at
NASA Headquarters in Washington.

For high resolution photos to support this release, visit:

http://www.dfrc.nasa.gov/Gallery/Photo/

For information about NASA's aeronautics research programs, visit:

http://www.aeronautics.nasa.gov

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