Since helipads are not an enemy to the chopper it will not shoot at it. Instead use the invisible targets addon (it is in the addons depot). There are four kinds, one is an IR target (so it will be treatrd as an air threat by AI), one is Armor target (it will be treated as an armor threat), One is a laser target (so an A10 with an LBG bomb will attack that), and the last one is like a man, so that will be attacked the same way infantry units are engage (a helo with rockets will use rockets, otherwise it will use the mounted chain gun (Hind, Apache, Super Cobra). All four invisible targets have sides for East, West, Civilian, and Resistance. If you want to camcreate or creatVehicle the targets here are there names:
"LesIETA": Invisible Target Man, East
"LesIWTA": Invisible Target Man, West
"LesIGTA": Invisible Target Man, Resistance
"LesICTA": Invisible Target Man, Civilian
"LesIAETA": Invisible Target Armored East,
"LesIAWTA": Invisible Target Armored West
"LesIAGTA": Invisible Target Armored Resistance
"LesIACTA": Invisible Target Armored Civilian
"LesIIETA": Invisible Target IR East
"LesIIWTA": Invisible Target IR West
"LesIIGTA": Invisible Target IR Resistance
"LesIICTA": Invisible Target IR Civilian
"LesILETA": Invisible Target Laser East
"LesILWTA": Invisible Target Laser West
"LesILGTA": Invisible Target Laser Resistance
"LesILCTA": Invisible Target Laser Civilian