Airfoil Modelling

Testing the flight physics one thing that struck me was that beyond the critical AOA for a given airfoil we were simply setting the coefficient of lift to 0.  I think the reason is that most of the charts only continue plotting maybe 5 degrees beyond the critical AOA.  However, I found a source for a symmetrical airfoil (no camber) which was taken all the way through 180 degrees of AOA!

The lift coefficient pretty closely follows a f(x) of sin(x/90*pi-0.04)+0.04 except for in those laminar flow regions from alpha 0 to 25 and 155 to 180. Although the drag is absurd at 45 degrees AOA, the lift produced is almost equal to that at the critical AOA of 15!