The process works fairly well for testing straight, level flight, according to Korsmeyer. However, what happens during take-off and landing is difficult to predict with supercomputers because air turbulence occurs. The wind sneaks back around and does unexpected things. That's where wind tunnel testing comes in. Testing a model in a wind tunnel, you get actual physics because you have real wind blowing over a wing.
Wind tunnels are chambers through which air flows during tests of airplane shapes.
In the tunnels, air is blown around airplane and rocket models to simulate flight. Pressure gauges, strain gauges, and other instruments attached to the models take readings while air blows through wind tunnels during experiments. Data streaming from the model instruments tell aerospace engineers how much lift, drag, and maneuvering performance an airplane model can generate through different angles of flight, and at various speeds, altitudes and conditions. New knowledge about airplane designs gained during wind tunnel tests helps engineers to decide if their ideas are working, or if design changes must be made before expensive, full-size prototype airplanes are built. Running a large wind tunnel can cost tens of thousands of dollars per hour, with the exact cost depending upon the tunnel, the number of personnel needed, as well as any special equipment required.