Thread: Discussion Airfoil Optimization with XFOIL
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Old May 25, 2010, 08:30 PM
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Originally Posted by rocketmagnet View Post
Well, I guess the way to do it is to test each airfoil at a range of AoA, and select the best for that airfoil.

I would certainly remove the max camber constraint. Remember, the purpose is simply to achieve the maximum lift, at the expense of everything else. Although I think there should be a fixed chord and Re (my personal preference being 20cm and 35000, but could be anything).

I ended up just running it for an angle of attack of 10 degrees. Using this assumption, the optimizer will naturally find airfoils that stall around 10 degrees at that reynolds number.

It was run for awhile, but I had to do stop and restart a lot because XFoil convergence issues at those extreme conditions (and the extreme shapes generated) made the optimization problematic. However, I did get a Cl over 1.8 (precisely, 1.8224) without too much trouble, though the airfoil would be pretty much unusable for an actual model as the performance everywhere else is very poor.

What I found was that the optimum camber was around 7.3%, but the angle at the trailing edge kept increasing to get higher lift. It probably would have increased more if I kept increasing the upper allowable limit. I stopped it at 35 degrees, which means the trailing edge is basically acting like a flap. Anyway, here are the results.

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