Why should v1 ...
Why do it if it's not fun?
Join Date: Jul 2001
Location: Bournemouth
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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
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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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
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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Why do it if it's not fun?
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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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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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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?
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?
