Drag Polars
thought there was a bit of confusion on here, so perhaps this will clarify things!
The drag polar has minimum drag at maximum L/D, which also equals maximum CL/CD. For aircraft operating well below Mcrit, max L/D occurs when induced drag and zero-lift drag are equal. The variable with the largest effect on minimum drag speed (Vmd) is weight, which increases the induced drag. Vmd increases as weight increases.
Once compressibility effects become significant, particularly when Mcrit is exceeded and wave drag becomes a factor, the drag polar changes partly because the CL/AOA gradient reduces in the transonic region but also because CD increases rapidly as the Mach number gets much above Mcrit.
Vmd is the best RANGE speed for a propeller aircraft and best ENDURANCE speed for a jet aircraft.
For endurance, you want minimum fuel flow. For range, you want to maximise speed/drag or minimise drag/speed. For a jet this occurs at 1.316 * Vmd.
WF