Having trouble taking aim at the chopper while zombies are constantly harrassing you? Try doing the Zombie Ride to jump on top of the shelter in the park. That way, the zombies can't bite you. When you are up there, there is also some glitch where the helicopter is unable to shoot you very well. I think it's because the chopper aims at Frank as if he was standing on the ground.

I was only shot maybe twice while on top of the shelter. Take your machinegun or the Real Mega Buster and aim toward the helicopter when it is about to come straight at you. Once it starts its approach, turn around 180 degrees, aim straight up toward the sky and start shooting your weapon. You should be able to hit the rotor within a couple tries. You really only need to land one good shot, so if you use this technique, all you have to do is line your shots up right and you will hit the chopper as it passes over you. Just aim straight for the center when it starts coming towards you, then quickly turn around 180 degrees, (hold down to turn around completely) then aim for the sky and start shooting.

Forget to destroy the military helicopter and now all the zombies are dead (Day 3)? There is still a way to get on the shelter without using the Zombie Walk! Go to the parking lot located far west on your Mall Map. Get in the red car and drive to the shelter.

Once the car is near the shelter, a glitch will happen where if you position Frank under the edge of the shelter roof and jump, he will grab on to the ledge and pull himself up. It has worked every time I've tried.

I was shot about five times on top, but it was worth it because the helicopter misses most of the time. Everything else about destroying the helicopter is pretty much covered in the hint above this one, and it works very well.