How to determine airfoil AOA

[zbrubaker]

I have some airfoils I've drawn up using coordinate data (eppler 205, selig 3021, etc) and I'd like to know if airfoil data is created with the airfoil at a zero degree angle of attack. If not, how can one determine the AOA of an airfoil?

[Andy W]

Draw a line from the LE to the TE..
..a

[Sparky Paul]

This is the defintion of angle of attack (AOA)..

[zbrubaker]

Thanks guys. It's so simple I didn't think that could possibly be it, but I guess it is.

[Sparky Paul]

Note the zero AOA is not the same as the zero lift angle for a cambered airfoil.
And incidence is also something else, with a different reference.

[zbrubaker]

How does one determine the zero lift angle?

[Sparky Paul]

Wind tunnel.. on a polar, it's where the Cl line crosses the zero alpha line..
the old style polars are easier to comprehend than the new fangled gee-whiz style.. :)