F l u t t e r Analyses
Symmetric and antisymmetric flutter analyses of the B-61 store configuration were conducted with the production pylon simulation and with the decoupler pylon simulation. The analyses were the bases for evaluating the effectiveness of the decoupler pylon as a flutter suppression device on the B-61 store configuration. These analyses were conducted for subsonic Mach numbers of 0.6 and 0.9 and a supersonic Mach number of 1.2. The subsonic unsteady aerodynamic terms were computed with the doublet lattice aerodynamic program and the supersonic unsteady aerodynamic terms were computed with the kernel function procedure. The initial analyses were made to compare the production pylon and the decoupler p y l o n with the current design spring. These comparisons were made at an altitude of sea level for t h e three Mach numbers. A standard k solution flutter analysis was made. The flutter speed and flutter frequencies These flutter w e r e compared at a damping value of 0 . 0 2 . speeds and flutter frequencies are shown on Table 8 . The production pylon analysis shows high flutter speeds for the symmetric cases and low flutter speeds for the antisymmetric cases. These results agree with the airplane flight test experience, where the limited amplitude oscillations are antisymmetric. The flight experience is such that as speed is increased, the magnitude of the oscillation increases, therefore a clear cut flutter instability is experienced on the airplane. The predicted antisymmetric flutter frequency also matches the frequency experienced in flight. The flutter analysis of the airplane with the decoupler pylon results in a low symmetric and a high antisymmetric flutter speed. Therefore the decoupler pylon has the effect of solving the antisymmetric flutter problem and creating a symmetric flutter problem. The low symmetric flutter speed 13
