Stochastic Variations in Aerodynamic Influence Coefficients (AICs) on Flutter Prediction of a Generic Wing

Traditionally designers account for uncertainties during aircraft design by keeping a fifteen percent excess flutter margin for the entire operating envelope of the aircraft. Probabilistic methods can be used to account for the uncertainties and understand their role vis-a-vis the flutter margins. In this paper we present the effects of aerodynamic uncertainties on the flutter characteristics of a generic wing. The Aerodynamic Influence Coefficients (AIC’s) were calculated using the Doublet Lattice method (DLM). The AIC’s were first corrected using the experimental data from the AGARD aeroelastic tests. Monte-Carlo studies were then carried out to calculate the impact of uncertainties in the AIC’s on flutter of the wing, using a uniform random variable. To understand the impact on the flutter margin, variations in AIC’s were studied for a range of uncertainty levels (different σ values) and correlation lengths. Results show that, as far as sensitivity to flutter velocity is concerned, variations in AIC’s are less important than variations in structural parameters. Additionally, uncertainties in the aerodynamic force and moment in the outboard section of the wing have larger effects on the calculated flutter speed then the root section.