Robust design optimizations of an airfoil are conducted to increase the aerodynamic performance and to reduce the performance deterioration due to the manufacturing variations of a human-powered aircraft. Randomly-generated perturbed designs are evaluated for the robustness index. Maximum performance difference is used for robustness definition to prevent the worst performance deterioration. The approach can design less-sensitive airfoil against the manufacturing variations while improving the performance compared to initial airfoil. In addition, the essential parameter to control performance and robustness is discussed.