A modification to the flutter derivative model

•In current form, Flutter derivatives are not one-dimensional functions.•Alternative governing equations are proposed to solve this problem.•The aeroelastic coupling effect is “decoupled” by approximated modeling strategy.•The number of independent aeroelastic parameters is reduced from eight to five.

There is an ambiguity in the original equations for the identification of flutter derivatives. The analysis in this paper shows that, for the two degrees of freedom (2DOF) model, these derivatives in these equations are, in fact, three-dimensional functions instead of one dimensional functions of reduced frequency. Alternative governing equations are proposed in this paper to solve this problem. These new equations “decouple” the aeroelastic coupling effect by approximated modeling strategy. The number of independent aeroelastic parameters is reduced from eight to five. Nonlinear nature of the aeroelastic coupling effect is unveiled. The nonlinear identification method is presented to retrieve the new set of aeroelastic parameters. Wind tunnel experiments were conducted to show the effectiveness of the newly proposed equations.