Why is a wind tunnel important in aircraft design?

A wind tunnel plays a crucial role in aircraft design primarily because it allows engineers to test aerodynamics by simulating airflow over models. This process is essential, as understanding how air interacts with an aircraft’s surfaces directly affects flight performance, stability, and efficiency.

By utilizing a wind tunnel, engineers can observe how different design features, such as wings and fuselage shapes, influence airflow patterns and drag. This testing can provide valuable data, including lift and drag coefficients, which can be used to optimize the aircraft's performance before it is built. Furthermore, changes can be made to the design based on the results from wind tunnel testing, ensuring a more aerodynamically efficient and effective aircraft design.

Other options focus on aspects like engine performance, passenger safety, and structural integrity, which are all important, but they do not directly relate to the primary function of a wind tunnel in designing and refining an aircraft's aerodynamic characteristics.