If anybody cares, here's the result of my sunday afternoon relaxation, trying the [link=http://xflr5.sourceforge.net/xflr5.htm]QFLR5[/link] program mentioned in [link=http://www.rcuniverse.com/forum/fb.asp?m=9070389]the other thread[/link]:

Only wing and empennage are rendered because I was interested in the tip stall problem. Fuse and nacelles would obstruct the view of the wing airflow and have been omitted. The wing center section has NACA 2215 airfoil, the outer wing panels are tapered to 2206, just like the original. Only the elliptical wing tips have washout but not the swept panels with the ailerons, just to elaborate the problem. Size of the model is 1:12 (95" wing span), weight 4.5 lbs, c/g 6.9" behind center leading edge.

With all due caution, the program shows the general problem of the DC-3 wing, even if not exactly.

The first picture shows the case aoa=6 degrees, what is twice the incidence angle. So the fuselage is not exactly in flight direction. Speed is 22 mph, the lift coefficient 0.66. That is the cruise flight tested in the simulator. The wing's upper surface is blue indicating low pressure. The orange grid behind the wing indicates induced drag, the pink grid behind wing and tail indicates viscous drag. The red line on the wing from tip to tip shows the point of transition from laminar to turbulent flow. It's slightly aft of the maximum thickness, as normal. The green lines behind the wing are streamlines showing the decent tip vortices.

Now compare the second picture, aoa=8 degrees. Bigger induced drag, very noticeable tip vortices, and a more forward transition line. Most interesting is that the transition line comes close to the leading edge outboards near the wing tips. Only 1 or 2 degrees more aoa and the transition reaches the leading edge and stall begins. (At least that's my interpretation.) That's what happens also in the simulator. So the wing's lift coefficient seems to be limited to 0.85 or 0.9 due to early tip stall.

Now the tapered and swept wing panels have 3 degrees washout. Still the elliptical wing tips have additional washout, like before. Of course, the tip vortices are smaller at aoa=6 degrees and the laminar/turbulent transition is more aft near the wing tips. Lift coefficient is only 0.60, as is due.

Gain is 2 degrees more aoa (10 degrees) and a 0.97 or 1.0 lift coefficient - not too bad. What the pictures don't show is that the stall is now more abrupt and severe. The complete outer wing stalls now at once while the stall progressed from the tips inboards when the wing had no washout.

Neat! (Sorry for the metric units.)

As I said before, I would pass washout and build (and use) flaps. But maybe the models have different airfoils and wing layout and behave differently. Compare this interesting [link=http://www.rcuniverse.com/forum/fb.asp?m=1604561]post[/link]. Or the calculations are just wrong...