Airfoil Shape and Low RN

[Don Cooper]

Looking through forums and literature, the consensus appears to be that, for a given class (e.g., undercambered, flat bottom, symmetrical) and similar thickness, airfoil shape doesn't make much difference at slow flier Reynolds Numbers. However, when I compare airfoils using the Garton & Ormah (I think the spellings are right) Airfoil Comparison Tool, I see significant differences in drag polars for various airfoils. Are these drag polar differences realized in the real world? Is it worthwhile to worry about the details of airfoil shape at slow flier Reynolds Numbers?

[Dave Robelen]

Hello Don,
Speaking from personal experience, it make a bunch of difference. The range of Rn that many of the small light models fly is definitely sensitive to shape. Comparisons with different undercambered airfoils show sensitivity to the point of maximum camber, the amount of undercamber, and the leading edge shape. The other area of difference in flight is the airfoil pitching moment which must be trimmed out with the stab. This can also change the L/D. The same applies to the flat bottom sections. The R/C Hand launch community works very hard on subtle differences in the differen sections. I have seen noticable difference in my light scale models when the wing contour is varied, or the leading edge is sharp or rounded, or the leading edge has some upsweep.
Regards, Dave

[Don Cooper]

Dave,

Thanks for the info. I had wondered if I was wasting my time worrying about airfoil shape. It appears that I am not.