DC-4, DC-6, DC-7...
An interesting item about the wing used on these series of aircraft...the airfoil section was not changed much, only the washout required for the later models...and the span for the -7C model.
My dad was engineering project manager on the DC6 and DC7 programs, and he mentioned Douglas tried various types of wing tip treatments, to try to reduce drag further...tip tanks, fences, small winglets...and nothing worked better then the original tip design.