You've got the right idea. Set the trim at about neutral or slightly higher, and then set the throttle so that with the stick all the way back it is idling; then when you pull your trim back, it kills the engine. This way you don't inadvertantly kill the engine when you throttle back in flight. If you haven't started the engine yet, you may need to fine-tune the adjustment when you do. At idle, the throttle barrel is just barely open, doesn't take much to keep the engine running. Welcome to RC Universe, and r/c airplanes. Good luck flying.