A wind tunnel test uses a test chamber to evaluate air flow around an object and is often used for measuring the aerodynamic efficiency of vehicles and airplanes. In most wind tunnels, only a smaller scale model of an actual vehicle will fit inside the test area. The test vehicle model is mounted in the middle of the chamber and air is moved through the tunnel duct by a fan system. This simulates air flowing over a moving vehicle under various wind conditions. The test model is usually instrumented to measure wind forces, air pressure, vehicle speed, wind angles, and other airflow characteristics.