Determining XV-15 Aeroelastic Modes from Flight Data with Frequency-Domain Methods

The XV-15 tilt-rotor wing has six major aeroelastic modes that are close in frequency. To precisely excite individual modes during flight test, dual flaperon exciters with automatic frequency-sweep controls were installed. The resulting structural data were analyzed in the frequency domain (Fourier...

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Bibliographic Details
Main Authors: Acree, Jr, C W, Tischler, Mark B
Format: Report
Language:English
Subjects:
Aerodynamics
AEROELASTICITY
CONTROL
FLAPERONS
FLIGHT TESTING
FREQUENCY DOMAIN
MATHEMATICAL PREDICTION
ROTOR BLADES
STRUCTURAL PROPERTIES
TILT ROTOR AIRCRAFT
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Summary:The XV-15 tilt-rotor wing has six major aeroelastic modes that are close in frequency. To precisely excite individual modes during flight test, dual flaperon exciters with automatic frequency-sweep controls were installed. The resulting structural data were analyzed in the frequency domain (Fourier transformed). All spectral data were computed using chirp z-transforms. Modal frequencies and damping were determined by fitting curves to frequency-response magnitude and phase data. The results given in this report are for the XV-15 with its original metal rotor blades. Also, frequency and damping values are compared with theoretical predictions made using two different programs, CAMRAD and ASAP. The frequency-domain data-analysis method proved to be very reliable and adequate for tracking aeroelastic modes during flight-envelope expansion. This approach required less flight-test time and yielded mode estimations that were more repeatable, compared with the exponential-decay method previously used.