Wind tunnel tests were conducted to investigate lift to drag ratio improvement by the leading-edge flap the outboard wing on an SST model at transonic regions. Force measurements and surface pressure measurements were performed for the SST model with and without outboard leading-edge flaps of 5 and 12.2 degrees deflection angles. The lift to drag ratio was improved due to a reduction in the drag component when flaps deflected, because the flow was attached to the leading edge surface of the wing. The optimum flap deflection angles to attain the maximum lift to drag ratio at a fixed lift coefficient were estimated using experimental results.
