I think that if you want to stick to the old MRC = 1.32 Vmd, you’d better restrict your operations to low level. There may be some validity in making it a discussion point for low level operations, e.g. depressurised operations at 10,000 feet, but at normal optimum cruise levels for Boeing and Airbus aircraft, MRC and LRC are defined by Mach Number, i.e. all operations are above Mcrit and the low speed drag polars attributable to EAS are only a portion of the total drag.
A very heavy 4 engined jet aircraft might have a MRC speed defined by EAS alone very early in the flight, but not for long.
The original post did refer to Boeing and Airbus aircraft, so here goes for a B777-200ER at 240,000 Kg (529,100 Lb) at F/L 350. Published Holding Speed is 279 KIAS. Assuming that Boeing have given me a 5% buffer above Vmd for speed stability, that makes VMD equal to 265.7 Kt. Multiplying by 1.32 makes it 350.7 KIAS, hey wait!, I can’t do that, it’s way above Vmo, and what’s more, is supersonic!
OK then, let’s assume that Boeing gave me 10% above Vmd for extreme speed stability (unheard of). That makes Vmd equal to 253.6 KIAS, and multiplied by 1.32 equals 335 KIAS, still above Vmo but we’re sub-sonic now at a mere M 0.962, way way above Mmo as well.
What of very high flying aircraft like the Learjet 45? Mcrit is about 0.72, and at higher levels (up to F/L 510 for this aircraft), Vmd no longer exists, minimum drag is defined by Mach Number. Mmd is always greater than Mcrit, except at the cross-over level where Vmd = Mcrit. So 1.32 X 0.72 = M 0.95 – Any Learjet pilots out there willing to take a run up to M0.95 to prove or disprove the theory?
For aircraft operating way below optimum altitude, the 1.32 Vmd story is a nice little bit of theory. For everyday operations at or close to optimum level, it has no relevance whatsoever. It’s all about Mach Number.
Regards,
Old Smokey