Left: The tail-rotor gearbox of Greg’s Align T-Rex 450 Pro heli shows the aft end of the torque tube with the bevel gear. Alignment and proper lash are important on both ends.

This small heli has a direct-drive tail. The tiny wires come through the tailboom and connect to the control board. They are routed and secured to avoid getting tangled in moving parts.

Below: This cutaway view of the front end of a T-Rex 450 Pro’s tail-rotor drive shows how the front bevel gear off of the end of the torque tube meshes with another bevel gear on a shaft to the straight gear that is driven by the main-rotor drive train. It seems complicated, but it’s robust and solid when properly set up.

This is the torque tube from Greg’s Blade 180 CFX heli after it came in contact with the ground. The ends break off easily, but nothing else is damaged. A pack of two replacements is cheap and it takes 5 minutes to replace one. It is also self-aligning.

along with the security of the blades to the motor.

TT tail drives require nearly perfect alignment and gear lash (spacing). The alignment is usually accomplished by single or multiple support bearings inside the tailboom. Replacement shafts for my Blade 180 CFX come with a bearing installed midway. They simply slide into the tailboom on the shaft to support and align it.

The gear lash on the drive gears needs to be set so that it meshes properly but doesn’t bind. A gear that is too loose will often show curled edges from the shock of contact. Use a very thin piece of paper to set the lash. The shaft is a sacrificial lamb on most machines and cheap to replace. This protects the more expensive components when unexpected ground contact happens.

BD systems are simple affairs but require occasional care. They will loosen over time and need to be tightened by extending the tailboom in its mounts to take up the slack. There isn’t a magic formula, but you don’t want the belt so tight that it binds or so loose that it jumps the cogs on the drive gears. I change mine twice a season and give the new one a little bit of silicon spray to help prevent static electricity and condition the belt.

When replacing the belt, ensure that you twist it properly to maintain proper directional control. Belts should be soft and flexible. If yours is getting hard or feels dry, replace it.

Wrap-up: Maintaining your tail-rotor drive doesn’t take a lot of effort, but it’s extremely important that you give it

One of the things to check for on a belt- driven tail is alignment. This belt is running true down the center of the tailboom and centered on the gear.

some love. You might find that regular inspection and tuning will alleviate some of those gremlins that have been chasing you. Make inspections part of your overall maintenance routine. You’ll be glad you did.


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