Using Frequency-Domain Methods to Identify XV-15 Aeroelastic Modes

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) with cross-spectral and transfer-function methods. Modal frequencies and damping were determined by performing curve fits to transfer-function magnitude and phase data and to cross-spectral magnitude data. Results are given for the XV-15 with its original metal rotor blades. Frequency and damping values are also compared with earlier predictions.