Originally Posted by framer
Is VMD purely a function of weight and therefore the same IAS at FL380 or 2000ft for a given weight?
No, at FL380 VMD would be higher due to Mach effect on L/D.
Originally Posted by deefer dog
Best L/D speed for a given weight would give max range, but because the engines may not work as efficiently at this lowish speed, a better mileage per pound of fuel is obtained at a speed somewhat above that of best L/D. Is that it?
No it isn't. Best L/D speed VMD is the speed V for minimum drag D.
VMR is the speed for minimum D/V.
For a parabolic drag polar in still air VMR is equal to VMD times the 4th-power root of 3.
If it assumed that engine efficiency (thrust specific fuel consumption) is constant, then VMD is the speed for max endurance and VMR is the speed for maximum range.