Detailed images of how to complete Chopper Stomper, Stunt Man and Car Jump
Yipee-Kai-Yay - 10G
Now you have discovered the whereabouts of the helicopter pad getting this next achievement is also simple. You need to hit a hovering agency helicopter whilst driving the Agency SUV. Sounds tricky, unless you and a friend are in control. One of you should hover a helicopter inches above the ground and allow the other player to drive into you. Simple.
Chopper Stomper - 10G
More helicopter action that works best as at least a duo. Ground Stomping (unlocked at physical level 5) an enemy after jumping from a helicopter should be relatively easy, but to make it even more so, why not draft in a friend? One player should collect an Agency helicopter whilst the other should locate a Freak hole and activate it. Rather than fight the hoard, player 2 should draw them out, the bigger the crowd, the better. This means that when your co-op pal jumps out of the helicopter they will find it pretty hard to miss everyone.
Stuntman - 20G
If you have a little patience and poor driving skills then a helicopter can help you and a co-op pal get this achievement too. Stuntman requires that you complete all 40 stunt rings in the game, but some of them are very tricky. However, you can cheat by attaching a car to a helicopter, using the sticky mines unlocked early in the game, and flying through the rings. Make sure that one of you is a pilot whilst the other is sitting in the car, this method can be quite time consuming, but you can admire the view.