Helicopter cheat
An easy way to get a better helicopter with more rockets & better gun is to call in a "vehicle repair drop" or "vehicle ammo drop", throw your smoke signal and move away to get a clear shot. The helicopter that does the delivery is a Mafia owned one, shoot the pilot (easiest to do with sniper rifle) and the chopper should crash land without to much damage, calling in the vehicle repair drop is usually best that way you can use the crate to repair the downed chopper as it will get some damage from the landing.