Transonic flutter and response analyses of two 3-degree-of-freedom airfoils

Abstract

Flutter and time-response analyses are performed for a NACA 64A006 conventional and a MBB A-3 supercritical airfoil, both oscillating with plunge, pitch, and aileron pitch degrees-of-freedom (DOF's) in smalldisturbance transonic flow. The aerodynamic coefficients are calculated using the transonic code LTRAN2NLR. The effects of various kinds of aeroelastic parameters on flutter speeds for the bending-torsion, bendingaileron, and torsion-aileron branches are studied. The flutter speeds associated with the bending-torsion branch are plotted against Mach number for different parameter values and the transonic dip phenomenon is demonstrated. To study the flutter modes, the flutter speed, amplitude ratio, and phase difference at different Mach numbers are plotted against the mass ratio for both a 2DOF and a 3DOF case. Time-response results are obtained for the NACA 64A006 and the MBB A-3 airfoils at M=Q.85 and 0.765, respectively. Based on the same sets of parameter values, the flight speeds used to obtain all the neutrally stable responses are very close to the flutter speeds obtained in the flutter analysis. The principle of linear superposition of airloads is used in the flutter analysis, but not in the response analysis.