Ask an Explainer

The answer, in short, is it is a trial and error process. To start, pressure drag is very disadvantageous in flying, so the major goal of the streamlined shape is to minimize pressure drag, which is why it takes on the tear drop shape. To compare, an extreme alternative would be a blunt object, like a baseball, this is all pressure drag and very little skin friction drag. To minimize the pressure drag, engineers lengthen the airfoil out. Although this results in higher skin friction drag, skin friction drag is less interrupting. Although ideally, engineers could have a very long airfoil that has minimal pressure drag, and if they make it a very smooth surface minimal skin friction drag, this is very difficult in practicality. The goal then is to find the smallest length that minimizes the skin friction drag and the pressure drag. Making the plane into a streamline shape minimizes the pressure drag, caused by air pushing differently in different places, but increases the friction drag, caused by air rubbing against the plane and slowing it down, and vice versa. Still there is a minimum for which there would be the least amount of drag and this would be the dimensions engineers would apply to their planes. Luckily, engineers can use computer models so that they don’t need to build every potential design in full.