# Aviation/Flying/VMCa speed

Question
In the book Aerodynamics for Naval Aviator it says that for each degree of bank angle towards the good engine your Vmc reduces by approximately 3 kts.

That is, banking towards inoperative engine, your Vmc might get pretty high, right?

Reading some VMC theory, I don't get it how VMC changes so much if you bank. I assume that is if you want to maintain straight and level flight, right and it doesn't apply if you want to turn. That is, if after takeoff, climbing at Vy, you are in a turn 30 degrees bank angle and your top engine failed, your VMC is likely above or at actual speed and thus resulting in an out of control scenario? You can't roll level using opposite aileron or you just can't maintain straight and level using that bank angle? I don't get it at all.

Other example, when your engine fails, you may not be able to arrest the initial roll, that means if the airplane rolls, let's say 20 degrees towards the dead engine, when it fails, your actual Vmc equals your actual speed considering this scenario after takeoff when you are usually about 20 kts above published Vmc. So, again you may lose control at all if the bank angle - Vmc relation is correct.

I also watched some videos where in single engine operation, light twins were banked normally during low and slow flight in single engine flying a normal traffic pattern. If so, they would lose control if VMC would be really increased when banking.

This theory also feeds the old never bank into dead engine rule. I'm not a ME rated pilot, but I hope will start my ME training soon, so at least I would like to be ready at least on the theory part of the issue which actually is the one which confuses me.

So what's the truth?

Thank so much!

1) In the book Aerodynamics for Naval Aviator it says that for each degree of bank angle towards the good engine your Vmc reduces by approximately 3 kts. That is, banking towards inoperative engine, your Vmc might get pretty high, right?

In such a scenario of banking into the dead engine Vmc could be higher than anticipated. Flght tests decades ago found that if a pilot flew straight and level with the slip/skid indicator ball centered while engine out, a loss of control could occur almost 25kts above published Vmc. So yes, it could be quite high compared to that published in your AOM. For background reading, I suggest this article from Flight Training magazine (an excellent resource for pilots in flight training)-

http://flighttraining.aopa.org/magazine/1998/December/199812_Features_Replace_Mu

2) I don't get it how VMC changes so much if you bank...if after takeoff, climbing at Vy, you are in a turn 30 degrees bank angle and your top engine failed, your VMC is likely above or at actual speed and thus resulting in an out of control scenario?
You can't roll level using opposite aileron or you just can't maintain straight and level using that bank angle? I don't get it at all.

Yes, in such a scenario the aircraft could depart controlled flight but there several factors affecting that probability. Banking into the operating engine creates a horizontal component of lift that enhances rudder effectiveness. This is when Vmc is at its lowest. When Vmc is high and you have very little or no rudder effectiveness to work with, your ailerons aren't going to help you keep your aircraft under control in such a situation.

3) Other example, when your engine fails, you may not be able to arrest the initial roll, that means if the airplane rolls, let's say 20 degrees towards the dead engine, when it fails, your actual Vmc equals your actual speed considering this scenario after takeoff when you are usually about 20 kts above published Vmc. So, again you may lose control at all if the bank angle - Vmc relation is correct.
I would agree, especially considering the factor of Vmc + 25kts I mentioned earlier.

Good Luck with your ME training!

Aviation/Flying

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#### D. Norkus

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