just thought i would share my accumulated knowledge for bringing down Heli's with an RPG.
there are 2 different easy targets. you want to go for a heli flying in or out of combat, preferably not gaining or dropping altitude. the other easy target is a heli turning it's nose around for a strafe run.
in the first scenario you have to just guess on the fly where you think the heli will be when you fire your RPG. take speed in to consideration. you will always have to lead Scout's more then Attack's or Transport's. after a while you will get used to where you want to aim and you won't have to think about it as much.
in the second scenario, again aim for where you think the chopper will be. this is the easier of the two especially if your going after an Attack Chopper as they fly like a landyacht. Scout's are a little trickier especially if they are gaining/dropping altitude as they turn for a strafe. make sure you account for the drop of the RPG relative to how high the chopper is.
once you get good at it start taking shots at Scout's as they circle strafe, those can be challenging. not to many tips for that beyond what i previously mentioned.
always practice. any chance you get take some shots at a chopper flying overhead or heading to a flag. you may even surprise yourself once you get good at taking the drop of the RPG itself into consideration. i think that is really half of the struggle.
when your good at hitting choppers with RPG's you will be a better and more well rounded Engi and far more useful to your team. now you can deal with all forms of vehicles instead of just land of just air.
ALWAYS STAY AWAY FROM USING THOSE STIGLAS! YOUR BETTER THAN THAT!