Quote:
Originally Posted by dcb
I'm not quite ready to discount the bernoulli principle as being a significant contributor to lift.
One of my favorite RC sailplanes in my little fleet uses a SD7037 airfoil (pictured below). It is fast and has good penetration upwind (important when you don't have a motor), but it doesn't like slow very much.
But what I want to point out is that here it is drawn in normalized position, the leading and trailing edges are on the 0.00 line. So that when the air splits at the leading edge at this angle of attack, it should "rejoin" at the same exact height at the trailing edge. If there were no bernoulli, this would not create lift.
But it is creating quite a bit of lift. The zero lift angle of attack for the SD7037 is actually -3.29 degrees, meaning you have to lower the leading edge to get this to stop making lift.
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I'm not sure the normalized position based on the leading edge and trailing edge makes sense. We know that aerodynamics at the rear is more important than the front right? So why can't the rear-facing slope of the wing be more important than the front-facing slope? That is the part where flow gets pulled downward to meet the wing, which I think is how most lift gets created.
In order to reach zero lift, you have to angle that rear-facing slope so that it's balanced by downforce on the rear-facing bottom surface.