Modal parameters estimate of AH-64D apache helicopter from flight data and correlation with numerical model

The objective of this paper is the assessment of an estimating modal parameter approach that uses helicopter fight data to be used for finite element model validation. This approach uses both Hilbert Transform Method (HTM) to estimate the biased Frequency Response Functions (FRFs) from fight test response accelerations and the Entropy statistical index to identify possible harmonic loading contributions to the dynamic response. Once the harmonics component have been recognized, modal parameters of the flying structure are estimated using any residue/pole-based estimating method applied to the biased FRFs free of any harmonic loading contribution. The proposed methodology has been assessed considering the Apache AH-64D Helicopter, whose data have been recorded during fight tests. Finally, the estimated modal parameters are used for a preliminary validation of the helicopter finite element model through correlation.