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Regarding the airfoil selections. This is something extremely important. Not that they be exact becuse at model scales, especially 1/4 or smeller some of the old profiles really are not that great. The French Eiffel sections are very thin, have rather narrow radius and quite undercambers. Makes for dreaful reynolds numbers at scale sizes and a bit tricky with internal structure. A lot of the british airfoils, especially the RAF 14 and 15 have poor model characteristics. Of all the later german arfoils are wonderful The Gottingen series, especially the 396 and 387 are almost identical in a lots of ways for the long type tried and true clark Y.
Accruacy of the airfoils naturally should be picked so the plane is relatively easy to fly. No nasty surprises. Of course it follows that as the scale goes up 1/3 or 1/2 that the realistic shapes perfom better and better, although even at these sizes the inherent nature of them can lead to unpleasant surprises.
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