Wow Evan, though I'd really like to agree (what I do in general here), especially in this case there's a downer. I did the math (quad wing loading) with DC-3 spec's from Wikipedia: Because the DC-3 is such a big slow-flying featherweight full-size (I hear you laughing) you'd have to build it to 20 lbs weight in 1:6 scale (190" wingspan) and even only 1.2 lb in 1:12 scale (95" wingspan) to have her fly "scale" speed. (I hope I've got the initial question right and made no calc error.) Those would be real featherweights, even 1:6.

I wholeheartedly agree not to give up and build as big and light as you can. There are several successful examples for instance on the annual Aspach e-flight meetings, not only [link=http://www.rcgroups.com/forums/showthread.php?t=294293]2002[/link] (especially the BAe 146 and other models by Hans Bühr). The result may not fly "mathematically scale" (just faster) but it should still look very scale.

If you aim for the the original cubic wing loading, which is sometimes seen as a measure for correct scale behavior, the 1:12 version could weigh even 14.5 lbs what should be possible (lighter still being better). Wing loading would be 34 oz/sqft what is not really low for a 8 ft high-aspect-ratio wing but is not bad either. In this case, I would find flaps instrumental in getting scale landings, though. The washout is advisable at this wing loading, and flaps would additionally help cure the tip-stall problem.

For a scale take-off and climb, plan for a thrust-weight ratio of less than 0.45 (even 0.35 should be enough) and use low-pitch props, just sufficient for target speed. That will help you keeping the weight low (small motors and batteries), maybe even more than a c/f skeleton framing construction with thin shell Ã* la Hans Bühr.