Estimation of Critical Aeroelastic Damping Using Dynamic Eigen Decomposition of Sensor Measurements

For certification of airplanes, aeronautical industry has primarily relied on aeroelastic damping extrapolation. The flight testing tailored for the task requires not only processing the signals in time domain but also conducting multiple tests at different flight conditions making it time-consuming and expensive. In this paper, a new frequency domain approach for aeroelastic damping estimation is proposed that can be used during the flight tests. It is based on the Dynamic Eigen Decomposition of the test data with an artificially imposed structural damping. From the dynamically decomposed data modified with the artificial structural damping, neutrally stable solutions are found in which the amount of the negative structural damping added is interpreted as the true aeroelastic damping at the subcritical point. This analysis is carried out following a constant Mach line but by changing dynamic pressures or equivalently, varying altitudes. Nyquist stability criterion is applied to the data as the two parameters – dynamic pressures and artificial damping – are varied. For demonstration, a numerical model of a straight but tapered wing with four flaps is examined. It is shown that the proposed method can yield aeroelastic damping of critical modes, i.e., lightly damped modes, at conditions far from the flutter condition without the need to repeat the test multiple times and hence is inexpensive and can be ideal for flight testing.