RE: Laminar Flow
Ahh, the Holy Grail – Laminar Flow
There are few experts outside of the professional aeronautical engineers, but a lot of informed amateurs.
To understand laminar flow, you have to study fluids. Think of the airflow as multiple layers of air sliding across your wing surface. Right at the surface of the wing, the lay may not even be moving at all, but the next layer is sliding past, but not at the speed of the airplane. Each successive layer is also sliding over the one below, and at increasing speeds. Eventually the air is at the free stream speed of the aircraft. All is well unless the layers start mixing with each other. At this point, the air quits being laminar, and become turbulent. This mixing takes a lot of energy, primarily due to the increased moment of the air, and so the drag is higher.
So the Holy Grail is preventing this mixing from happening for as long as possible. This is done on a wing by controlling the change in pressure gradients. Generally, laminar airfoils move the high point of the wing toward the trailing edge so to preserve the laminar flow as long as possible. However, these sections are very critical of surface waviness and surface finish. It takes very little to trip the boundary layer, and so a wing may need to have waves in the order of one part in one thousand in order to maintain the flow. Difficult, but not impossible.
Selecting the correct airfoil for your application depends on the size of the airplane’s wing sections and the speed that it flies at. You need to determine the Reynolds number that it will be working at when at racing speed, and determine the best airfoil from that information.