This paper proposes a time-varying sliding surface for a second-order sliding mode controller to improve the control performance and energy efficiency of a quad-rotor helicopter. The time-varying sliding surface is designed with a nonlinear function to provide varying properties of the closed-loop dynamics in order to reduce energy consumption. It is shown that the second-order sliding mode technique, known as a generalized super twisting algorithm, providing a robust controller and a nonlinear sliding surface is effective in reducing the energy consumption. A Lyapunov stability analysis is described to prove the stability of the proposed method. The effectiveness and reliability of the proposed method are evaluated by performing experiments several times using a quad-rotor helicopter experimental testbed under wind disturbance.