Take the taill boom all the way off the main frame so you can look down it and get the belt so it doesn't have any twists in it. Then with the tail boom in the same orientation as when it will be when attached to the frame, rotate the belt 90 Degrees to the left (when viewed from behind), put it on the gear and tension the belt...all should be well (check that the tail rotor rotates up into the main rotor)