Because it works. Most airplanes we commonly encounter look pretty much the same, according to PVPA's July speaker, Jeff Schroeder. They have an engine in the front, a wing and a tail. Some are high wing and others low wing. Some have a wheel in the front and others have one in the back. But, all in all, they are pretty much the same because most airplanes are a compromise.

As a result most GA airplanes have a reasonable range, travel at a respectable speed for an acceptable distance and carry moderate a load in relative comfort. Some airplanes may go very fast, but not too far and only have one seat. Others travel long distances, slowly, are cramped for space and the ride is less than smooth. Still others carry big loads for long distances very quickly, but you might find it difficult to find hanger space. These specialty aircraft, however, are found in limited numbers.

Jeff went on to discuss airfoils and wings and how their shape affects performance. Basically, when it's all said and done, "An airplane stays in the air by pushing the air down," he said. But there are other factors such as lift. The higher the camber (that's the curve of the airfoil), the more the wing will lift. But high camber wings tend to pitch down more than a thinner airfoil when they stall. But there is another tradeoff. Thinner airfoils, which stall at higher speeds have less of a tendency to pitch down [due to a more stable center of pressure]. Tapered wings with an airfoil, which is thinner at the tip than at the root, are more prone to spin when stalled since the tips tend to stall first and you loose aileron authority. Unless, of course, the wingtips are washed out (bent up), which adds drag.

Weight and balance is also a favorite topic with him. He took us through a lively explanation of the relationship of center of lift and center of gravity. The bottom line is that an aft C/G may give you slightly better performance but a forward C/G is more stable and to a point, more desirable. His advice is, "Don't tease the tiger, he may bite. Those C/G limits were put there for a purpose, respect them."

Following his presentation on aerodynamics, Jeff discussed an airplane he has built, the BD-5. He went on to thrill and delight the gathering with an accounting of his first flight in the airplane, complete with an engine failure before the first pattern was completed.