Things You'll Need
Instructions
Test the tension of the helicopter by pushing against the tension belt. Imagine there is a line that crosses the axis of the belt gear, and goes through the back gear. If the belt goes more than three-quarters of the way across this line, it is too lose; if it doesn't go that far, it is too tight.
Loosen the screws around the tail mount so that you can slide the tail boom in and out. Don't remove the tail boom, but loosen it just enough that you can adjust its length.
Pull the tail boom further out to tighten it, or push it in to loosen. Adjust the boom until you think it is the correct tightness.
Tighten the screws around the tail boom. Tighten until the boom doesn't slide anymore.
Re-check the belt tension. Again, imagine there is a line between the axles of both gears. If you push from the right, and the belt reaches exactly halfway between the imaginary line and the left side, it is the correct tension. There is a diagram of this tension in the Trex 450 manual (see the References section.)