6150 rpm and spinning.
My experience with it is from the first few months.
The tanks took more ammo to kill from behind than what you could carry and that really put me off.
As for air targets, more often than not, it is the ground target that wrecked the helo.
At least that's the way it was in majority of the games I played in.
1: That explains a bit, but only a bit.
2: Tanks have NEVER taken more than 3 (for with reactive armor) RPGs to kill from the rear. You carry 4, potentially more with certain kits.
3: A combination of horrible pilots and stringer's being somewhat OP at the start. Sadly then ended up nerfing stingers into the ground instead, you know, balancing them.
4: That's the random game roulette, and much like my experience with PS2.