Flutter testing requires that accurate estimates of aircraft modal parameters be made in a time critical manner. Since these measurements are made on aircraft in-flight, or on wind tunnel models, there are high levels of noise in the data due to unmeasured turbulent forces and other factors. Cost related time constraints often dictate that test engineers must generate frequency and damping estimates for critical modes in two minutes. These estimates are utilized to decide whether it is safe to advance to a test point in a less benign area of the flight envelope. Although an unexpected flutter event is unlikely, the implied risk to flight crew and aircraft or wind tunnel model, weighs heavily on the test engineers. Incorrect estimates could result in inaccurate characterization of the stability boundary. Spatial filtering is investigated as a means of improving the speed and accuracy with which frequency and damping estimates may be made. The structural response information contained in many response measurements acquired simultaneously at various locations on the aircraft is condensed down to a few channels, each of which accentuates a single mode of interest. These modal coordinate responses may be accurately fit with simple models, improving the accuracy and speed Versus time and effort ratio of the estimation process.
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