I dunno, I've plenty of planes to take out the ack, usually (this is for the small fields), I'll dive in and open up after the ack has been firing at me for some time (I adjust heading/angle a lot) and strafe down the runway length wise... taking out 3 or 4 acks on the right or left side, then going back to finish it off.
That's the best method, for me, for small fields... and if you are careful you won't get touched in any plane. Of course, the faster you go- the more heading/angle adjustments you will have to do.. I like to come in around 350MPH.
I believe the 20mm will open up first on you, then the 37mm.. but it might be the other way around. The max range for one of those is 8K.. or maybe both.. that's when they will start firing at you, but will be very inaccurate.
And the manned ack don't have tracers, they didn't anyway, so it's always best to get those if you don't see one of the ack implacements firing at you.
-SW