Wind tunnel tests and theoretical investigations on the effect of a localised mass on the flutter of a delta wing with fixed root

Abstract

Summary.--Wind tunnel tests and theoretical investigations have been carried out to study the effect of a localised mass on the flutter characteristics of a delta wing. The experimental work covered a wide range of spanwise and chordwise positions of the mass c.g., variation of the magnitude and radius of gyration of the mass itself, and the effect of the stiffness distribution of the wing. The theoretical work was more limited in its scope and was primarily intended to investigate the reliability of the theoretical approach to this kind of problem. These investigations have shown that the flutter characteristics of a delta wing carrying a localised mass are primarily dependent on\\' the location of the mass, its magnitude and the stiffness distribution of the wing itself. The flutter speed with a localised mass judiciously placed may be from three to four times that obtained with the same mass in a bad position. A localised mass in the region around the structural axis generally has an adverse effect on the flutter characteristics, while locations well aft, towards the trailing edge, are usually favourable. Particularly high flutter speeds are often associated with a localised mass close to the leading edge, but some caution is necessary, especially around the mid-span position, as the flutter characteristics in this region are very sensitive to variations in actual mass. A fair measure of success was obtained in the theoretical investigations, the calculated flutter characteristics being in reasonable agreement with experimental results in most cases. Calculations based on resonance test modes gave remarkably good results in certain cases, but in general, this method showed only a slight superiority over the arbitrary mode approach.