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Vibrations
Vibrations are probably the most common problem in helicopters. This makes sense with all the rotating parts involved.
Head or Tail?
The first thing you have to do is to determine if the problem is main rotor or tail related.
The head operate at a lower RPM than the tail , so Tail vibrations will be at a higher frequency.
Head Vibrations
Head
vibration symptoms are often manifested in a swirling shaking motion in
the skids. The skids will move left/right as well as front back.
The tail will shake up/down. Flexable horizontal tail fins will have
the tips shaking up/down.
Tail Vibrations
Tail
vibrations very often cause gyro problems like tail twitches. Severe
Tail vibrations will cause side to side motion in the skids but at a
higher frequency than Head vibrations. Most evident will be a vertical
tail fin vibrate side to side especially noticable at the bottom of the
vertical tail fin.
Causes of Vibrations
Here is an outline of possible causes of vibrations prioritized in order of probable cause.
Head Vibration
New Helicopter
1) Main Blade balance
2) Flybar balance
3) Mainshaft Bent
4) Mainblades out of track
5) Incorrectly assembled mainblade grips/dampers/spacers/thrust bearings
6) Faulty Mainshaft bearing
7) Faulty machined rotor hub
8) Bent shaft on motor
9) Improper shaft diameter of pinion (3.17mm pinion on a 3.0mm motor shaft)
10) Faulty dampers
11) Bent Flybar/Flybar paddles not level
Helicopter rebuilt from Crash
1) Mainshaft Bent
2) Main Blade Balance
3) Flybar Balance
4) Torn dampers
5) Bent Flybar/Flybar paddles not level
6) Incorrectly assembled mainblade grips/dampers/spacers/thrust bearings
7) Faulty Mainshaft bearing
8) Bent rotor hub
9) Bent shaft on motor
10) Improper shaft diameter of pinion (3.17mm pinion on a 3.0mm motor shaft)
11) Bent linkages
Tail Vibration
New Helicopter
1) Tail blade balance
2) Loose tail box screws
3) Bent Tail shaft
4) Faulty Tail bearing
5) Loose Tail blade grip
Helicopter rebuilt from crash
1) Bent Tail shaft
2) Faulty Tail bearing
3) Tail blade balance
4) Loose tail box screws
5) Loose Tail blade grip