  Zimmerman and Weissenburger's flutter margin method is widely used to
estimate the aeroelastic coalescence flutter speed. In contrast to aeroelastic
decay rates, the flutter margin exhibits monotonic decay with respect to
airspeed redering it effective in extrapolating the flutter speed using flight
test data conducted at pre-flutter airspeeds. This paper reports the
generalization of the Bayesian formulation of the flutter margin method by
Khalil et al. developed to tackle measurement and modeling uncertainties. This
paper improves the predictive performance of the previous algorithm by
incorporating the joint prior of aeroelastic modal frequencies and decay rates
among airspeeds in order to better estimate the joint posterior of modal
parameters using observational data. The modal parameter prior is constructed
using the classical two-degree-of-freedom pitch-plunge aeroelastic model whose
system matrices (e.g. structural stiffness and damping matrices) vary randomly.
Such joint modal parameter prior enforces statistical dependence among
posteriors of modal parameters and the associated flutter margins across
airspeeds. Numerical studies demonstrate a considerable reduction of
uncertainties on the predicted flutter speed obtained from the generalized
Bayesian flutter margin method. This improved algorithm can cut cost by
reducing the number of flight tests and better assess the uncertainty against
aeroelastic flutter.
