Nonsteady load distributions are investigated on a thin airfoil having oscillating flap, when there is a narrow hinge gap, in an invicid incompressible flow. The angle of attack is assumed to be zero in front of the hinge gap.
First the problem is attacked numerically through the POSSIO's integral equation to compare it with the analytical method. The logarithmic singularity in the kernel function is treated with special care. Second the method of matched asymptotic expansion is used to analyze the problem. This brings simple closed expressions.
Comparisons of results of the two methods show excellent agreement each other, when the gap width to chord ratio is less than 0.1, say. In appendix, a simplified method is presented where no inner solution needs to be considered; it is useful for gap/chord ratio less than 0.01.
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