V mc

[cosworth211]

Hi,

Does anyone know what v - speed V mc is?? ( In respect of a Beech Duchess). Its listed as 65kts and described as "red line".

I've tried the search engine but without luck.

Many thanks. :)

[Mad (Flt) Scientist]

I believe there was a discussion about it recently in another context, but I can't find it.

The more common use of the abbreviation Vmc or VMC is Minimum Control Speed, but I don't think that's what you're seeing.

The less common seems to be "manoeuvring capability" speed, and is the speed up to which full control inputs are stressed. That may well be what you're seeing.

[Sans Anoraque]

http://www.asiresource.com/instrum.htm

[cosworth211]

Thanks for the help guys :)

[ricky-godf]

Vmc is the minimum speed (in the air) at which you can maintain directional control of the airplane following the critical engine failure, using the rudder and maximum 5° bank toward the live engine.
As far as I remeber, it is calculated considering:
- maximum take-off thrust
- airplane trimmed for take-off
- worst CG position (aft limit)
- maximum take-off weight at MSL
- most critical take-off configuration but undercarriage up!
- out of ground effect
- dead engine NOT feathered unless an auto-feathering device is provided.
- maximum bank allowed 5°
- maximum foot load 150 lbs

Vmc has to be 20% greater than Vs.

Do not confuse with Vmcg (minimum control on the ground) or Vmcl (minimum control during landing), however just Vmc is indicated on your ASI with the red line.

Hope this helps

[Mad (Flt) Scientist]

Vmc has to be 20% greater than Vs

Agree with most of those statements, but not that one. There's no requirement that minimum control speed be higher than stall speed - and in fact it's preferable that it be lower. Since that means you have no practical asymmetric thrust controllability limits at low speeds.

Just to clarify some of the other statments about the conditions for Vmc(a) demonstration

As far as I remeber, it is calculated considering:
- maximum take-off thrust * usually it's "maximum normally expected" or some similar statement; which means the rated max thrust isn't used, since that's considered the minimum you'll get (or take credit for). Instead some number in excess is used, to allow for engine-to-engine variation.
- airplane trimmed for take-off
- worst CG position (aft limit)
- maximum take-off weight at MSL *actually, minimum weight is the key here, since increased weight gives effectively an increased bank angle allowance. Vmc(a) increases with decreased weight, all other conditions being equal
- most critical take-off configuration but undercarriage up!
- out of ground effect
- dead engine NOT feathered unless an auto-feathering device is provided.
- maximum bank allowed 5°
- maximum foot load 150 lbs *or 180lbf in some rules/amendments, I believe)

[BigGrecian]

VMC is set and is a speed - in practice where you train you never go below blue line speed - doing so in the skills test will earn you a fail.

Hope the break is doing you some good.
See you soon.

[Farrell]

You need to update that profile of yours BG!!;)

[ricky-godf]

quote:
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Vmc has to be 20% greater than Vs
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yes, that is bull****.
I don't know where I get it, sorry.

Cheers