difference between Vmc and Vmca

[powdermonkey]

Hey guys,
Can anyone tell me what the exact diff. is between the two? I know its minimum control speed in the air with the critical engine inop, but was told there was a diff between the two. Can anyone highlight?

[bulfly]

VMCG : Minimum speed, on the ground during takeoff, at which the aircraft can be controlled by the use of primary flight controls only, after a sudden failure of the critical engine, the other engine remaining at takeoff power.
VMCA : Minimum control speed in flight at which the aircraft can be controlled with a maximum bank of 5 degrees, if one engine fails, the other engine remaining at takeoff power (takeoff flap setting, gear retracted).
VMCL : Minimum control speed in flight at which the aircraft can be controlled with a maximum bank of 5 degrees, if one engine fails, the other engine remaining at takeoff power (approach flap setting).
VMCL-2 : Minimum control speed in flight at which the aircraft can be controlled with a maximum bank of 5 degrees, if two engines fail on the same side, the other engines remaining at takeoff power (approach flap setting).
VMC - as far as I know minimum control speed has to be defined for a flight phase, thus it makes no sense :confused:
Hope this helps!

[FlyingForFun]

Vmc - the minimum speed at which the aircraft can be controlled if an engine fails. It does not have a specific value which you can look up in the manual, like the other figures do. Instead, it changes depending on many other factors (power set, altitude, flaps, gear, pilot strength, etc.)

For example, you might ask (http://www.pprune.org/forums/showthread.php?t=262217) how flaps would affect Vmc. But it is not correct to ask how flaps affect Vmca, because the flap setting used when measuring Vmca is pre-defined and can not be changed.

FFF
-----------

[john_tullamarine]

Vmc and Vmca generally used interchangeably ...

[Old Smokey]

In complete agreement with John_T, the convention is that if Vmc alone is quoted, it refers to Vmca.

Nice listing bulfly :ok:

Regards,

Old Smokey

[FlyVMO]

"Vmc - the minimum speed at which the aircraft can be controlled if an engine fails. It does not have a specific value which you can look up in the manual, like the other figures do. Instead, it changes depending on many other factors (power set, altitude, flaps, gear, pilot strength, etc.)"

In the US it is a required part of the Multi Engine Class rating to perform "VMC demos" using the VMC definition given by FFF (or similar). I was surprised at first when I didn't have to do this as part of my JAA MEP. Performed incorrectly though it can be a dangerous maneuver (single engine stall leading to a spin in an a/c that was never spin tested or designed with such loads in mind), so I suppose thats why.
The purpose is to recognize the loss of ability to maintain control after previously having established control when engine out. It can be surprisingly subtle as the airspeed decays, and the heading just starts to drift slowly at first. As noted, the speed at which this occurs will vary according to alt, temp, how tired the engines are etc.
Anyway I thought it was an interesting experience....

[powdermonkey]

Thank you all, I understood Vmca.
so Vmc is really a generic term and needs the ac to be in a specific config and phase of flight for it to have a given IAS as a minimum? ie Vmc in straight level flight with the loss of 1 engine will have one value, and Vmc in a landing config with flaps 10 gear down and critical engine failed will obviously have another........?
PS FlyVMO, I was shown as part of the ME class training " departure" essentially demonstrating that at low speed with full rudder authority, the ac is no longer controllable. We used Vsse...71kts I believe for the Duchess, but I don't think that it is required to demonstrate it in the flight test.