The simplicity of the original design makes the NACA duct adaptable to most any surface. In modern aircraft, the duct is used to vent or feed secondary systems.© Paper courtesy of NASA ...

The NACA duct is a low drag intake that is only fully functional if placed correctly on the car. However, in the ideal position it draws in air with minimal disturbance to the flow.

Chevrolet teamed up with the National Advisory Committee for Aeronautics, or NACA, for this Jam Handy-produced 1941 film reel titled "Taking the Air." ...

The new SA-1 helmet is the first ever helmet with NACA duct Airflow Technology. In simple words, the air flow system of the said helmet is favoured in Racing car designs and aircrafts.