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The DC-3 is a very popular and widely used aircraft, yet has low speed tip stalling risks due to the design of its wing, which at the time of its development represented the leading edge in drag reduction for larger and faster mono-wing aircraft in the 1930s.

Specifically, the swept and tapered wingtips, at high angles of attack, would stall first.

Did the original design, or later modifications, include slats to remedy this issue? Is there any way to reduce this risk other than retractable slats?

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Although it's technically possible, you aren't going to find slats retrofitted to a DC-3 (nobody would ever pay for it).

But yes, in theory you could improve the DC-3's stall behaviour and single engine performance very cheaply with Vortex Generators which can be thought of as a "poor man's slat". VGs increase stalling AOA by between 1/3 to 1/2 of what you get with a slat (say, about 18-20 deg, vs 25 with slats) depending on the airfoil.

VGs have huge benefits on light twins, reducing stall speed, taming stall behaviour, improving aileron response, and often reducing Vmc to the stall when installed on the fin. They are quite miraculous, although they can be a headache because they are usually glued on and if the kid you pay 20 bucks to wash your plane knocks off too many, you are grounded until you fix them.

I can't find anybody that sells a VG kit for the '3 although it does seem to be possible to install them on a wing with boots. Possibly the DC-3's airfoil requires VG placement far enough forward that the boots are in the way (each airfoil has a chord wise sweet spot and if they are too far aft they don't do anything). Or maybe nobody has thought of doing it yet.

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  • $\begingroup$ Just got done viewing the NACA film on this. They used a sharpened leading edge installed between engine nacelles and fuse to create a warning "buffet". Also they seemed to apply a little INSIDE aileron in the recovery. This made sense as the aileron extends pretty close to the wing tip. I surely would let go of the elevator. $\endgroup$
    – Robert DiGiovanni
    Jun 16, 2019 at 0:45
  • $\begingroup$ @RobertDiGiovanni Note that what I'm describing is an entire array of VGs across the leading edge. I've thought of making a set and putting them on my own plane (a homebuilt) but I need to find out the proper chordwise location for my airfoil. $\endgroup$
    – John K
    Jun 16, 2019 at 1:20
  • $\begingroup$ I have heard 6-10% of the chord from the LE, so you were right about possibly being too close to de-icing boots. Of course, with your own plane little steps might be best. I might try the sharpened leading edge on the LE closest to the fuse, and VGs at the wing tips. Maybe a little washout too. But that old plane looks real good to me. $\endgroup$
    – Robert DiGiovanni
    Jun 16, 2019 at 1:40
  • $\begingroup$ Greatest engineered conveyance in history in my opinion. Can you think of any other complex transportation machine, designed 85 years ago, that businesses still, two decades into the 21st century, still purchase as a tool, to put to work making money as opposed to using as an expensive toy to show off. I can't. $\endgroup$
    – John K
    Jun 16, 2019 at 3:19

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