How is aviation possible? The answer is not difficult as long as it concerns balloons and airships: They fly because they are filled with gas that makes them lighter than air. But how do airplanes fly even though they are much heavier than air? The explanation has to do with the airflow around the wings and its different velocities on top and at the bottom of the wings. These phenomena can be visualized by the soap film channel.
Profile in the soap film channel. Credit: TU Hamburg-Harburg.
The soap film channel consists of an aluminum frame of approx. 2 meters height. Soapy water is continuously fed from a container to an upper opening. The soapy water flows down from the opening between two thin nylon threads spanning a soap film 20 centimeters wide and 80 centimeters high. Illuminated by white light, a fascinating play of colors can be observed when a body (e.g. wing profile) is inserted into the flowing liquid. Variations in velocity cause a change of thickness which in turn can be seen through iridescent colors of the soap film. This experiment gives a first idea of the different flow velocities near a wing profile.