Another possibility is dissimilar air-to-air combat simulation (someone will provide the correct description and acronym I'm sure - DAC?).."
USN calls it DACT, Dissimilar Air Combat Training. Topgun was the premier example of that in USN.
And yes, making a gun attack on a helo gunship (that has a turret) with a fighter is not easy. Your best bet is to stay out of range of the helo's gun and use a missile, preferrably a radar guided one rather than IR.