Harry
I agree totally with you in the other respect. Practicing a V1 cut or EFATO by pulling the power lever to FI increases drag and increases Vmca by a substantial margin. Obviously Zero thrust is used to simulate either the engine secured or initially at least autofeather operation. At light weights there could be only a small margin then between say V2 and Vmca. Again I use the B200 as example. The new models are certified to Part 25, meaning they run to transport category numbers. At max weight V2 is 111 KIAS. If autofeather was to fail, then Vmca will rise from 91 KIAS to 108 KIAS. Thats a 3 knot margin between the them - f**k all. Everybody here is going on about gradients, windmilling etc but bottom line is that if these aircraft are certified in the US then they do not need to meet these requirements in their basic form. If they have a shortcoming modifications such as MANDATORY autofeather can be employed and performance credits are then given, but these have to be functional at all times they are required or else the aircraft is not airworthy. Obviously some aircraft such as the Dash are so overpowered that this is not an issue. For some such as the B200 it is. The autofeather must be tested each day and the aircraft is grounded if it does not work. I believe the Bras is the same. It would be interesting to find out what a "light" V2 would be for a Bras as well as Vmca in the event of autofeather failure. I'm sure it would be tight. Obviously the only way to recover from a Vmca departure is to reduce power and lower the nose to increase airspeed. Who the hell is going to do this at a few hundred feet AGL as their aircraft is rolling and descending - I doubt I would.
Interesting point you make about the margins above Vmca for V2.
You are so right, margins are tight so good technique with speed control
Is important for maintaining control as well as achieving the desired performance.
I don’t recall Vmca for the Bras or the margin between V2, someone else may be able to help with that?
From my recollection of performance for FAR part 121; V2 = 1.1 Vmca or 1.2 Vs and doesn’t change whether auto fx is operative or not, as the prop is assumed to be windmilling in the engine out case.