Go to the top of Mt. Chiliad, where there is a Camper and Journey. It is an open area. Enable the "Spawn Vortex" code, then just drive off and hold A. You cannot move up or down, but can steer it. This trick does not always work. Go to the tall building in Los Santos that has the parachute on top. Go to the top of that building and enable the "Spawn Vortex" code. Drive it off the top and pull back. It will glide down smoothly to the ground.