The forces and moments on a two-dimensional airfoil executing harmonic motions in a pulsating stream are derived on the basis of nonstationary incompressible potential-flow theory, with the inclusion of the effect of the continuous sheet of vortices shed from the trailing edge. An assumption as to the form of the wake is made with a certain degree of approximation. A comparison with previous work applicable only to the special case of a stationary airfoil is made by means of a numerical example and the excellent agreement obtained shows that the wake approximation is quite sufficient. The results obtained are expected to be useful in considerations of forced vibrations and flutter of rotary-wing aircraft for which the lifting surfaces are in air streams of variable velocity.
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