Vmc Question- tgrayson would you help?

[jwp_145]

Hey guys,

MEI checkride coming up in a week or so and I have a question regarding Vmc...actually two.

I need a simple way to explain why a higher weight decreases Vmc during a turn.

Also, is this a simple/accurate enough explanation about why a sideslip increases Vmc: A sideslip increases Vmc because the relative wind is striking the rudder at an angle, thereby reducing its effectiveness and ability to counteract the yawing toward the dead engine.

 

[SteveC]

<Moved to Technical Talk forum.>

 

[tgrayson]

I need a simple way to explain why a higher weight decreases Vmc during a turn.

During a turn? You mean during a bank? If you bank towards the good engine 5 degrees, you can achieve a higher sideslip in a heavier airplane than you can in a lighter one and so increase directional control of the aircraft, meaning a lower Vmc.

(I view the above as a "paper" increase in Vmc, meaning of no value in the real world, because you won't be banking 5 degrees toward the good engine, you will be banking to achieve zero sideslip.)

Also, is this a simple/accurate enough explanation about why a sideslip increases Vmc: A sideslip increases Vmc because the relative wind is striking the rudder at an angle, thereby reducing its effectiveness and ability to counteract the yawing toward the dead engine.

Yes, but I would offer two caveats: 1) That describes a sideslip toward the dead engine. You can overbank and generate a sideslip toward the good engine and you can decrease Vmc. And 2) I prefer to say the relative wind is coming at the *vertical stabilizer* at an angle, rather than the rudder.