As sailplane pilots point out, TINSFS (There is no substitute for span.) By far, for wings of reasonable aspect ratio, induced drag is much larger than parasit

As sailplane pilots point out, TINSFS (There is no substitute for span.) By far, for wings of reasonable aspect ratio, induced drag is much larger than parasitic drag contributions for a wing. It's really only when you get down into the relatively soupy flow around hobby RC sailplanes that you're meaningfully constrained by skin friction. Let me explain. The coefficients of lift and drag for wing sections are idealized, resulting from wind tunnel tests where the section spans the tunnel. This makes them effectively infinite in span, since there are no spanwise differences in the flow characteristics; All flow proceeds from the upstream direction, laterally parallel, over (and under) the section, and then down the end of the tunnel. Real wings, however, are finite in length. While there are a number of ways to think about what happens at the wing tip, not the worst is to say that high pressure air from under the wing leaks onto the low pressure side above the wing. (It's an oversimplification, but it mostly works.) This finite wing effect is associated only with the tip of a long wing; Flow around sections of a wide span wing near the root behaves a lot more like ideal wing section flow than flow close to the tips. This leakiness does a couple of bad things, and at least one not-so-horrible thing. First, it reduces the coefficient of lift for the span as compared to the wind tunnel flow. Second, it gives rise to induced drag, which is that rotationally energized flow leaving the wing tips (plus the fact that your reduced lift coefficient means you have to pitch higher, basically aiming more of your lift aft). Third, and the good(ish) bit, is that it mushes out the stall, at the expense of a lower stall angle of attack. (It's nice when stalls happen gradually, with warning, rather than suddenly.) Those raised wing tips you see are a compromise between parking and performance. They are about 2/3 as effective as they would be if they were horizontal extensions of the wing. Notice that I'm talking here about span, and not aspect ratio. Aspect ratio, pointedly, is not a substitute for span. If you doubled a wing's width, you would get no reduction in benefit from doubling its chord length as well, other than a possible weight penalty, or the skin friction drag to which I think you allude. As they say on Monty Python, "SPAN! SPAN! SPAN! SPAN!..." The one exception to this is very light craft at very low wing loadings, like RC sailplanes. (So-called "floaters.") Down there, the lift, and therefore induced drag, is so low that the parasitic drag begins to dominate, and you can choose an "optimum" span for a given flight weight. I forget the paper where I saw the derivation of that.