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Diagnosing RC Helicopter Tail Vibration / Shaking Problems

February 25th, 2008 · 2 Comments ·

Tail vibration or shaking is one thing many RC helicopter pilots are plagued with at one time or another and can be at times difficult to diagnose.

One of the reasons it’s so hard to diagnose is that there are so many things that can cause ‘the shakes’ and something that is seemingly a small vibration can be easily amplified and turn into a large violent vibration.

Chances are if you’re RC helicopter is shaking or vibrating that it’s caused by something that’s bent or unbalanced.

The first thing you’ll want to ask yourself is if you have you done anything different?

Have you replaced or removed the main rotor blades? Check to see that they’re balanced and tracking properly. Have you upgraded your gyro? Check the sensitivity settings and so on…

Often tail vibrations are something that may develop over time, so in the rest of this article, I’ll give you a step-by-step methodical approach to tracking down that unwanted vibration.

To help track down the problem, you first need to figure out if the tail is shaking from side to side or up and down.

1. If the tail is shaking in an up and down motion it’s likely that’s something unbalanced or bent in the head of your heli.

2. If the tail is shaking from side to side it’s likely something to do with the tail, tail drive system or gyro.

Diagnosing Up / Down Tail Vibrations

If the tail is moving up and down, chances are that’s it’s something in the head of your RC helicopter that’s not perfect. Here are a few simple things to check in order of perceived likeliness:

1. Have the main blades been balanced? Is their weight and center of gravity matched? Are the both tightened equally?

2. Have you checked the blade tracking? Are they aligned properly?

3. Is the pitch and pitch range of the main rotor blades and the flybar paddles equally matched?

4. Is the flybar straight and true? Is each side of the flybar of an equal distance from the center hub? Are the paddles aligned correctly?

5. The main rotor shaft could also be bent from a crash. You can usually tell just by looking at it, but if you’re not sure, try rolling it across a flat surface and see if it has a wobble.

6. While we’re on the main shaft, does it move up and down at all? Even slightly? It shouldn’t. If it does, make sure that the clamp ring is tight or consider adding a shim washer to tighten up.

7. Is your feathering shaft bent? A bent feathering shaft can lead to blade tracking issues. An easy to check it without removing it is to check the tracking of your blades. If they’re out of alignment it could be because of a bent shaft, so remove it and check it by rolling it across a flat surface.

8. Is there any slop in the ball links? If they’re loose, it may be time to replace them.

Video Of RC Helicopter Tail Shaking

Diagnosing Side to Side Tail Vibrations

Side to side shaking is typically caused by something in the tail or the tail drive system. Here are a few things to look for in order of significance.

1. Have the tail rotors been balanced? And are they both tightened equally? Although this isn’t usually much of an issue because of their size and weight, it’s still something you’ll want to look at, if only just to cross it off the list.

2. Also, check to see if your tail rotor shaft is bent. If you’re unable to tell visually, take it apart and roll it across a smooth surface.

3. The gyro sensitivity may be set too high and it may be trying to correct a small vibration and ends up making it a larger vibration. Try turning the sensitivity down and see if it goes away.

Other factors that could affect the gyro sensitivity setting is that it isn’t mounted properly using anti-vibration mounting tape (I prefer Zeal tape) or it’s too close to the main gear.

It could also be that your tail rotor blades are too big for your heli and are influencing the tail movements exponentially.

4. It could also be caused by a stripped rudder servo that’s having trouble holding the tail pitch. It’s easy to test: Simply power up your heli (disconnect the motor) and see if there’s any play in the tail or servo linkage. If there is, and the servo horn doesn’t hold, you have probably striped your gears.

Your rudder servo linkage could also be binding if the travel isn’t set up right in your gyro or mechanically.

Another easy way to test your gyro / rudder servo is to tie your RC helicopter down to something solid (work bench, table, cement slab) and bypass the gyro (connect the tail servo directly to the receiver).

5. If your tail rotor uses a belt drive system, the belt could be loose and/or slipping on the gear. If the belt feels loose or you can hear it slipping, try tightening it up. A loose belt can lead to slippage and ultimately jerky side to side tail movement.

6. Alternatively, if RC heli uses a torque tube to drive the tail, it could just be a very small bend in the tube, so take it out and visually inspect it.

Honey Bee King Head Vibrations

Less Common Causes Of Tail Vibrations

Once you’ve exhausted all the options listed above with no success, you might want consider some of these less common causes of unwanted vibrations.

1. You may have a bent ball bearing or one that has simply run out of juice so check them t see if they’re still running smoothly.

2. Check the damper O rings in the head in case they’re tired or worn out.

3. If you’re flying a nitro or gasser, a lean running engine can lead to vibrations – you might want to try richening it up a little.

4. Another fairly common cause when a RC helicopter isn’t setup properly is that there’s in imbalance in weight distribution. An easy way to check is to hang your RC heli by a piece of sting attached to the blade grips and see if it’s level.

5. If you’re using training gear, it can exaggerate any shaking big time, so try removing it and see if that helps. You can also try shortening their length so increase the resonant frequency.

6. All RC helicopters will have a resonant frequency at which it will vibrate and if everything else seems to be ok at first glance, try flying at a slightly faster or slightly slower headspeed.

Most RC helicopters will also get the shakes a little when spooling up until the main blades find their place and as the headspeed increases.

This is not a 100% exhaustive guide, but it should give you more than enough to get you started tracking down that unwanted vibration.

I’ll add some more too it in a bit, however if you have a problem you can’t find an answer to here, just leave a comment and I’ll try to help you track it down.

Have a question about this article or anything else RC Heli related? Ask it in our brand new RC Helicopter Forum and you'll get expert answers quick.

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Tags: RC Helicopter Articles

2 responses so far ↓

  • Dave // Jul 21, 2008 at 7:44 am

    Is there a procedure to properly adjust the pitch of the Flybar Paddles?

    Thanks,

    Dave

  • admin // Jul 21, 2008 at 1:04 pm

    Hi Dave,

    You can measure the pitch of your flybar paddles using a small pitch meter and adjust the pitch range using the endpoints on your Radio.

    If you don’t have a pitch meter, you can eyeball it by looking straight down the flybar.

    Just make sure your heli / radio is on and the pitch at 50% on your radio prior to making any adjustments / measurements.

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