Some recent developments in flutter of flat panels

The accuracy of the two-dimensional static aerodynamic approximation for flutter analyses is investigated by comparison with results obtained on the basis of exact linearized threedimensional potential flow theory. For unstressed panels, these results indicate that, for Mach numbers greater than 1.3, two-dimensional static aerodynamics is applicable over the whole range of length-width ratios greater than 1. The theoretical boundaries are also in good agreement with experimental data obtained from stress-free isotropic panels with length-width ratios from 1 to 10. For stressed panels, results using the approximate aerodynamics differ widely from the trends indicated by experiment; use of more exact aerodynamics does not alter this comparison, but inclusion of structural damping improves the correlation of theory and experiment. Experimental results for unstressed corrugationstiffened panels are also presented and compared with theory. In some cases flutter occurred at dynamic pressures as low as 2% of the predicted value. An analysis of the effect of panel boundary conditions shows that such highly unconservative predictions may result from failure to account for the deflectional stiffness of the panel supports. Application of this analysis to the test panels results in marked improvement in the flutter predictions.

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