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2 Answers

Understanding Vmc, Multi engine.

Asked by: 2299 views , , ,
Aerodynamics, Aircraft Systems

I am working toward my Multi add on and reviewing Vmc.  Understanding that as density altitude increases, Vmc decreases due to the loss of power that the engine is able to produce.  The question is, how do I calculate Vmc, if I already know current density altitude?

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2 Answers

  1. jeff on Mar 30, 2015


    Im not sure you can unless the manufacturer provides a chart with DA vs Vmc. To my knowledge, no one provides this kind of information. No one should ever be operating a twin at those speeds so there really is no reason to publish numbers like that even if they were known. What is more important is understanding the factors which affect Vmc. So if Vmc for your aircraft is 77, understanding that as DA increases, Vmc will tend to decrease becuase of the decrease in power on the operating engine. So while understanding the dozen or so factors which can affect Vmc is critically important, having an exact number is not. You should not be operating the aicraft anywhere near those numbers. Even when im doing training with students, and most of the examiners I send students to, will limit full rudder movement with their foot to have the student demonstrate Vmc as opposed to actually slowing the aircraft to the published Vmc.

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  2. Kris Kortokrax on Apr 02, 2015

    No one could provide that type of information. The chart would need to be predicated on operating the critical engine at full power with the other engine windmilling while at minimum operating weight with the most rearward CG (assuming gear up and flaps up, out of ground effect).

    As to your statement that one should not be operating the aircraft anywhere near those numbers, how would you suggest teaching and testing maneuvers like slow flight, power off and power on stalls?

    Examiners that I have spoken with relate that the FAA does not allow blocking the rudder during the Vmc demo because the PTS states:

    “applying rudder pressure to maintain directional control until full rudder is applied”.

    I realize that the Airplane Flying Handbook does mention blocking the rudder during training, but it doesn’t appear to be allowed on the test

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