Well, it seems that I'm not all wrong, there really is trim on real helicopters:
http://www.tomshardware.co.uk/forum/18368-13-adding-trim-helicopters#1281873

Quote from that reply:
"Force trim is (or at least was in all the UH-1s and AH-1s I used
to fly back 35+ years ago) merely a means to hold the cyclic in a given
position. You place the cyclic where you wanted it, hit the force trim
button, the cyclic stayed where it was (both in pitch and roll axis). But it
really did not MOVE a trim tab like in a fixed wing aircraft. If you wanted
to adjust the force trim, hit the button to turn it OFF, move the cyclic to
a new position, hit the button again to ON.. To be honest, I always found it
to be a real pain --preferred to fly with it in the OFF position."

I was just curious how real attack chopter with fixed weapons does it. Is there trimmer to lower nose without getting forward momentum... or is there some kind of angle you can lower your chopter nose, before forward momentum starts.

Maybe there is no such thing in real chopters, and maybe there should not be one in ARMA 3... But I just wanted to throw idea of this trimmer for lowering nose few degrees. You will need practise anyway with it, and you can't just hover around, as SGTIce said... I just feel, it could be more realistic that rockets/minigun is designed for ground targets too, or chopter is designed for ground attacks.