Assuming installation of a dielectric-barrier-discharge plasma actuator (DBD-PA) on a small fixed-wing 2-m-span UAV, a wind-tunnel experiment using a NACA23015 three-dimensional wing model with a chord-length of 200 mm and an aspect ratio of 3.5 was conducted. DBD-PA was installed at the leading edge. Flow-control capability was evaluated by time-averaged pressure measurement with changing the span-wise DBD-PA length. Results show that the condition of the controlled flow field changes abruptly around the span-wise DBD-PA length of 80 %, rather than changes linearly. This result is important knowledge for the installation of DBD-PA on a fixed-wing UAV.