Olendirk
18th Mar 2004, 15:49
Hi!
why should the v1 not be lower than the Vmcg?
COuld someone give me a logic answer?;)
Thanks!
od
FlyingForFun
18th Mar 2004, 15:53
Vmcg = minimum speed at which the aircraft can be controlled, on the ground, with full power on one engine, and the second engine inop.
V1 = the speed after which, if an engine failure occurs, you continue.
If V1 were less than Vmcg, and you had an engine failure at, or shortly after, V1, you would then have full power on one engine, and the second engine inop - at a speed which is lower than Vmcg, and therefore, by definition, the aircraft would not be controllable :confused:
It is generally fair to say that you do not want your aircraft to be in an uncontrollable state for very long ;) Therefore, you ensure that V1 is the same as, or higher than, Vmcg. This way, if an engine fails before Vmcg, it will also be before V1, and will therefore be followed by closing the throttles and braking - which is controllable.
FFF
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JeroenC
19th Mar 2004, 00:54
Clear explanation, FFF!
But why is Vmcg a minimum speed as opposed to a maximum?
And where does mcg stand for?
Tnx,
JC.
FlyingForFun
19th Mar 2004, 08:06
mcg = Minimum Controllabe, Ground.
The reason it's a minimum is because as you go faster, the rudder becomes more effective, and is better able to counter the asymetric effect of the remaining engine.
FFF
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Tinstaafl
19th Mar 2004, 17:40
To slightly turn around FFF's explanation:
At high speeds the yaw & roll produced by an engine failure is very controllable due to the large aerodynamic forces that the control surfaces can produce. As speed reduces these forces also reduce. At some point in the speed reduction there will no longer be sufficient force able to be produced by the control surfaces to counteract the adverse effects caused by the engine failure. You've just reached Vmc
On the ground there is a beneficial effect to aid controllability from the forces produced by the wheels. Nosewheel steering, differential braking etc all supplement the control surface forces used to counteract the effects of the engine failure hence Vmcg (ground) is usually different to Vmca (air)
As for V1 not being less than Vmc: Speeds >V1 means 'continue the take off'. With a hypothetical engine failure at a V1<Vmc, would you really want to get airborne at a speed that is less than what you need to control the a/c?