Old 16th Apr 2014, 01:29
  #82 (permalink)  
Join Date: Jun 2001
Location: Australia
Posts: 890
maybe if you consider that vmcA is only valid in the take-off configuration you would understand my post.
My aircraft (a turboprop) has a VmcL equal to stalling speed with landing flap at MLW.

It should come as no surprise at all then that Vmc is very much lower than Vs in the clean configuration. Even the classic Vmca is much less than Vs in the specific circumstances pertaining to an engine failure during take off.

Presumably, the size and design of the rudder/fin have been specified for the most limiting case (in my aircraft, a rated power go around at final approach speed & configuration). Inevitably, Vmc is less than Vs in some other configurations. It may be more than Vs in some configurations, in some aircraft.

This doesn't mean that pilots will or should attempt to fly below Vs! It's just a result of compromise in the design criteria, and the different aerodynamic laws pertaining to max CL versus directional controllability.
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