NF-15B #837's (71-0290) canards are tilted down during
a pre-flight, prior to a Lancets project flight. 1/12/09
Photo: NASA / Tony Landis
1/22/2009 - EDWARDS AFB, CA -- 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 such noise.
A sonic boom is created by shock waves that form on the front
and rear of the 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 with
special instruments. Global Positioning System relative positioning
was used to guide the pilot of the probing aircraft to the test
position and for accurate reporting of measurement locations.
NASA Dryden's NF-15B #837 takes off on a Lancets project
Photo: NASA / Tom Tschida
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.
NASA's modified NF-15B was 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
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 will also 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.
Source: NASA Press Release