The modal characteristics of high aspect ratio sailplane wings including the effects of bending and torsional rigidities

The modal behaviour of two high aspect ratio sailplane wings with cantilever boundary conditions is investigated by applying the dynamic stiffness method and using the Wittrick-Williams algorithm as solution technique. The wing is idealised as an assembly of bending-torsional coupled beams for which the frequency dependent dynamic stiffness matrix is established. A Fortran computer program is developed to obtain the natural frequencies and mode shapes of the wings. The bending and torsional rigidities of each wing are varied and their subsequent effects on the natural frequencies and mode shapes are examined. A detailed parametric study with the variations of bending and torsional rigidities shows some interesting results which can be of practical help to the industry when designing such wings. The illustrative examples chosen for the baseline wings prior to changing their rigidities are representative of existing sailplanes. The results are presented and discussed and the paper concludes with some remarks.