As I recall, from the TV documentary
Planes That Changed The World - DC-3 - the original DC-1 paper design and wind-tunnel models had wings with taper but no (or minimal) sweep. Perpendicular leading edge and angled trailing edge.
Wind tunnel tests revealed stability problems that the math hadn't predicted, resulting in a major redesign, including adding the sweep (and the fillet or fairing at the wing/fuselage junction, and numerous other tweaks) before the DC-1 prototype and DC-2/3 production aircraft ever flew.
Before:
http://caltech.discoverygarden.ca/is...tream/JPG/view
and after the changes:
http://www.airminded.net/dc3/dcwindtunneltest.jpg