An experimental and theoretical study of the effect of fuel on pitching-translation flutter

John L. Sewall
Dec 1957

Analytical flutter studies were made for 2 two-dimensional fuel-loaded wing models, and the results are compared with experimental results for bending-to-torsion frequency ratios near 1. One of the models was made so that water, simulating fuel, could be carried internally in three compartments separated from each other by sealed spanwise partitions. The flutter speeds of this medel for all fuel loads were highest for the compartmental-emptying sequence proceeding from front to rear. In the other model, fluid was carried externally in a geometrically scaled standard airplane fuel tank that was pylon mounted a distance of about two and a half times the tank radius beneath the wing. Experimental results for this model have been reported in NACA Research Memorandum L55F10. The results of flutter-speed calculations agreed well with experimental flutter speeds and flutter-speed trends when the analysis employed effective values for the mass and the mass moment of inertia together with theoretical slender-body air forces on the external tank and when the combined structural and fluid damping was considered to be zero. With the introduction of damping this agreement was improved for the internal-tank configuration and made worse for the external-tank configuration.

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