a088008
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That was exactly what I wanted to know. Thank you very much for the info.
One question. You mentioned that mushing occurs when the slope is shallow. Is this the case with my airfoil?
-Q.
[QUOTE]Originally posted by Daniel Nelson
You're right on the Cl/Cm vs alpha graphs; those are just the different values plotted at each alpha value. The Cl-alpha graph can also predict how violent the stall will be by how fast Cl falls off after stall. If it's a very shallow slope the stall will be mild and the plane should just mush through the stall; steep and your plane will fall like a rock.
The Cl vs Cd (drag polar graph) is in my (glider obsessed) mind the most important. It tells the designer over what range of Cl values the airplane is most effiecient. If you look at the graph, it shows that for a wide range of Cl, the Cd stays relatively low. Then, at some Cl, Cd starts increasing fast. That's called the drag bucket, and basically it says that as long as you stay between two particular Cls, then your plane is very efficient, but if you go over those, then you start incurring a huge drag penelty. Incidentally, this is not always where the airfoil starts to stall, it just happens that way with yours. Try running a symmetric airfoil from -15 to 15 degrees AoA, you'll really see the drag bucket form.
The other number that's also really important is the L/D, (Cl divided by Cd). It's the efficiency of the airfoil, and from it you can get the glide distance and duration. We glider designers will usually pick a Cl and alpha that maximizes either distance or duration and design around that.
As for the Xlr/C graph, I think it's showing Cl and Cm over the airfoil itself, with X/C=0 being the leading edge and X/C = 1 the trailing edge, although I don't know why or what that means. Personally, I don't think it's too important, I've never had to use it.
Hope this helps [/QUOTE]
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-Q
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All Forums >> RC Airplanes >> Aerodynamics >> XFoil and airfoil data 
XFoil and airfoil data - 
Don't have the link but I'll bet you can get it at the Charles River club site... 
I think that one thing the data is telling me (CL vs. alpha graphs) is that my maximum lift co-efficient (CL) is at alpha = 10.0 degrees and is about 1.3, so that must be the stall angle. Am I way off base here?