Vmc v. Vs Chart

[SennaP1]

Question for you guys.

So we all know Vs stays the same as altitude increases, where Vmc decreases (in non-turbocharged a/c).

SO the question I have is, for turbocharged a/c (i.e. PA34). On the Vs v. Vmc chart the Vmc line goes vertical for a bit and then meanders over. What is the altitude that that line starts to meander over (Vmc decrease). My guess is critical altitude. Thats what I've been telling my students. Want to make sure that is the correct answer.

Thanks in advance

Go Pistons!

 

[liv'n_on_credit]

You are correct. Critical altitude is the altitude at which the engine can no longer maintain a selected manifold pressure. The waste gate is completely closed, thus engine performance starts to drop. At this point, Vmc will start to decrease due to the decrease in engine performance.