This is an interesting discussion going here. Since the drag of the tail surfaces is a small part of the airplanes overall drag, don’t expect too much improvement. I say modified because the “cusp†trailing edge typical of the laminar flow series airfoils is not particularly suitable for control surfaces. That being said, if you use an airfoil section for the tail surfaces, a modified laminar flow with the maximum thickness at about 50% makes some sense as the tail surfaces operate at quit low angles of attack. These modifications may be limited in a scale model.Īs to tail surfaces, it’s hard to beat the conventional slab design. ![]() You must evaluate the drag reduction vs the added weight. Some areas of possible drag reduction include engine cowling, wing/fuselage interference, landing gear, etc. Light wing loading and high power loading are the two most important ingredients for speed. To go fast (assuming the engine size is a given) keeping the weight as low as practical will be more effective than almost anything else you can do. The AT-6 uses a slightly cambered airfoil that should work as good as any for a model. Since you mentioned giant scale, you can’t go far wrong using the scale airfoil. For such a flight profile, there is little to be gained with the laminar flow airfoils, especially since a slightly cambered airfoil with the maximum thickness a little farther forward usually gives better overall performance in turning flight. Radio control models are constantly turning to keep the aircraft in the confines of the airfield with little time spent in straight flight. However for something like pylon racing, any gain in the straight away will likely be lost in the turns where operation at high angles increases drag significantly. For flat out straight away speed where the angle of attack can be kept in the drag “bucket†they can be a good choice. In both cases low drag in cruise is an important design parameter, the P-51 as a long range bomber escort, and the Piper as a traveling machine. Such varied airplanes as the P-51 and the low wing piper aircraft use a laminar flow airfoil. However at larger angles, they are not any better (and sometimes worse) than more conventional shapes. The laminar flow (six series) airfoils do in fact have exceptional low drag coefficients at relatively low angles of attack. Your desire to make “fast†wings for racing involves a lot more than a laminar flow airfoil. 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. Selecting the correct airfoil for your application depends on the size of the airplane’s wing sections and the speed that it flies at. 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. However, these sections are very critical of surface waviness and surface finish. Generally, laminar airfoils move the high point of the wing toward the trailing edge so to preserve the laminar flow as long as possible. This is done on a wing by controlling the change in pressure gradients. So the Holy Grail is preventing this mixing from happening for as long as possible. This mixing takes a lot of energy, primarily due to the increased moment of the air, and so the drag is higher. At this point, the air quits being laminar, and become turbulent. All is well unless the layers start mixing with each other. Eventually the air is at the free stream speed of the aircraft. Each successive layer is also sliding over the one below, and at increasing speeds. 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. Think of the airflow as multiple layers of air sliding across your wing surface. To understand laminar flow, you have to study fluids. There are few experts outside of the professional aeronautical engineers, but a lot of informed amateurs.
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