DRYDEN FLIGHT RESEARCH CENTER - NEWS ROOM: NEWS RELEASES: FLIGHT EXPERIMENT DEMONSTRATES IMPROVED TEST METHOD



FLIGHT EXPERIMENT DEMONSTRATES IMPROVED TEST METHOD <h3>May 14, 
2001</h3> <h4>Release: 01-35</h4> Printer Friendly Version 
A flight experiment called the Aerostructures Test Wing (ATW) 
conducted at NASA's Dryden Flight Research Center, Edwards, Calif., 
successfully demonstrated a new software data analysis tool, the 
flutterometer, which is designed to increase the efficiency of flight 
flutter testing.

The experiment consisted of an 18-inch carbon fiber test wing with 
surface-mounted piezoelectric strain actuators. The test wing was 
mounted on a special ventral flight test fixture and flown on 
Dryden's F-15B Research Testbed aircraft.

Five flights consisted of increasing speeds and altitudes leading to 
the final test point of Mach .85 at an altitude of 10,000 feet. At 
each Mach and altitude, stability estimations of the wing were made 
using accelerometer measurements in response to the piezoelectric 
actuator excitation. The test wing was intentionally flown to the 
point of structural failure, resulting in about a third of the 
18-inch wing breaking off. This allowed engineers to record the 
effectiveness of the flutterometer over the entire regime of flutter 
testing, up to and including structural failure.

The actuators were moved at different magnitudes and frequency levels 
to induce wing vibrations and excite the dynamics during flight. 
Placement of the piezoelectric actuators was determined by NASA 
Langley Research Center, Hampton, Va. engineer Mercedes Reaves to 
maximize their effectiveness. The ATW experiment represents the first 
time that piezoelectric actuators were used during a flight flutter 
test.

"The data acquired during the Aerostructures Test Wing experiment will 
help us improve the way we model structures, and helps to validate 
the flutterometer concept" said Dryden project engineer David 
Voracek. "The data that was created from these flights will be 
invaluable to future flight flutter test engineers for research and 
training."

Potential benefits of this research include reduced time and cost 
associated with aircraft certification by lowering the number of 
flights required to clear a new or modified aircraft for flight, and 
provision of a structural dynamics database for industry and 
university flutter research.

The flutterometer is an on-line software tool that was loaded on 
computers in Dryden's control room for the experiment in order to 
access the flight data. With this new technology, flight data can be 
analyzed immediately using the newly developed software to determine 
the stability properties of aircraft in flight. It is designed to 
predict the flight conditions at which the onset of flutter may 
occur. In this way, the flight envelope of an aircraft can be 
determined more quickly and safely than using traditional approaches. 
The ATW experiment was the first time the flutterometer was used on a 
flight system that actually experienced flutter.

"The flutterometer represents a significant advance for flight flutter 
testing" said Dryden project engineer Rick Lind. "This tool can 
result in dramatic decreases in time and cost for military and 
commercial aircraft testing. The ATW experiment was a perfect 
demonstration of how the unique facilities at NASA Dryden can be used 
to develop tools that are beneficial to the entire aviation 
industry."

The concept of a flutterometer was initially conceived by Dryden 
structural dynamics engineer Len Voelker. Fellow engineers Rick Lind 
and Marty Brenner developed the flight data algorithms that made the 
flutterometer concept a reality. NASA was recently awarded a patent 
for the flutterometer. Its software program combines the strengths of 
analytical predictions and on-line estimation methods in the 
development of a flutterometer concept. The flutterometer software 
has previously been evaluated using simulations and wind tunnels 
along with flight data from several aircraft types including NASA 
Dryden's F-18 Systems Research Aircraft.

Flutter is the rapid and self-excited vibration of wings, tail 
surfaces, and other aircraft parts that can damage or destroy an 
aircraft component. Flutter is caused by the flow of air across the 
surface of the structure. Effectively, the aerodynamic forces couple 
with the structural bending and twisting to result in the destructive 
vibration. Flight flutter testing is the process of determining a 
flight envelope within which an aircraft is safe to operate. 
Traditional approaches for flight flutter testing do not accurately 
predict the onset of instability so this testing is a very 
time-consuming and expensive process.

The ATW was designed by NASA engineer Cliff Sticht and was 
manufactured by Fiberset, Inc., located in Mojave, Calif.



--nasa--

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