Approximate expressions for the generalised airforces acting on a rectangular wing of low aspect ratio oscillating harmonically in sonic flow at low frequencies are derived in this paper. The modes of oscillation considered are rigid modes and a small selection of flexible modes. Results are presented as the first few terms of infinite expansions. A brief description of the modes of oscillation and of the generalised airforces is given towards the end of the paper so that the results may be used without the main text of the paper having to be read.