Specifications

• Check the tail rotor shaft
Remove the tail rotor shaft and follow the directions in the Bent Shaft Checking section.
• Check the tail rotor bearings
Remove the tail shaft bearings from the helicopter. Put the tail shaft through each bearing
and spin it by hand. If the bearing does not rotate smoothly or feels gritty, then replace it.
• Tail rotor hub balancing
If the vibrations remain, then the tail rotor shaft and hub need to be balanced. Put the entire
assembly on a Tru-spin prop balancer or equivalent for balancing.
If the tail is vibrating left/right (usually noticeable by looking at the vertical tail fin) then this is
usually caused by problems in the main rotor system, such as a bent main rotor shaft or unbal-
anced main rotor blades.
If the tail is vibrating up/down, then this is usually caused by problems in the tail rotor system,
such as a bent tail rotor shaft or damaged tail rotor blades.
• On a Corona, the gear on the hollow TR shaft (56633) can become chipped, and it's very
hard to notice because the gear is inside the tail case. Try cleaning the old lithium grease
out of the tail case with a Q-tip and check for orange pieces of plastic in the old grease. If
you do find these plastic bits, then the TR shaft (56633) should be replaced.
• Tail vibration can be caused by tail blade holders being too tight. Some helicopter upgrade
tail hubs promise "dual or triple ball bearings which remove all slop..." This is a bad idea.
Most variable-pitch tail rotors are designed as a flapping hinge rotor which require slop in
the tail blade holder.
If this slop is removed, then this destroys the ability of the flapping hinge to equalize the
thrust from both tail rotor blades. This causes high-speed vibrations which may weaken the
tail blade holder screw and eventually shear it.
For more information on flapping hinges, search the web for the phrase "delta three angle"
or go to the following URL: www.scotiabladerunners.ca/delta.htm
26.2. Tail control problems
26.2.1. Tail keeps spinning and will not stop with HH gyro
The gyro reverse switch probably needs to be reversed.
• If the gyro reverse is correct:
When the tail moves left, the gyro will push it right until the turn is reversed.
When the tail moves right, the gyro will push it left until the turn is reversed.
• If the gyro reverse is incorrect:
When the tail moves left, the gyro will push it left some more until the turn is reversed.
Since the gyro cannot reverse a left turn by pushing the tail left, the tail will keep spinning
left forever.
Troubleshooting Common Problems
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