General what are the signs of bad thrust bearings (in flight)?

[helicc16]

Can bad thrust bearings cause vibrations?

I have never followed the factory-recommended thrust bearing replacement schedule ( after 20-25 flights) plainly because I am lazy.

But it would be nice to know when to replace them to prevent catastrophic failures.

Thanks, guys.

 

[Lee]

Thrust bearings don't tend to suffer from catastrophic failure. If they start to pit badly you may find pitch control becomes notchy instead of smooth.

 

[pvolcko]

Yeah. I really wouldn't expect bearings in the head to cause much issue unless they were really bad. Detecting notchy thrust bearings in flight... I suppose you might see it tend to "jump" on new pitch settings, or have a tendency to "lock in" to your most common pitch position (hover and forward flight most likely), resulting in collective and cyclic changes having a slight delay to them. It would likely be pretty subtle though. You may actually better detect such an issue in flight during cyclic inputs. If a bearing is sticking it would tend to cause a wobble as the blade tracks through the pitch change of the swash in a unsmooth manner, or perhaps it will track slightly off of your directional input until the controller dials in correction to overcome the sticking induced misdirection. The larger the cyclic input, the more pronounced the issue would be.

I'm guessing here. Trying to envision what a sticky blade holder would induce. I'm thinking it would cause the blade to change pitch slightly delayed as it would resist tracking the swash angle change through a rotation. It would eventually induce bearing fatigue on the swash as result, probably cause servos to heat up a bit more than usual too since they'd get more back force from the sticking blade and thus the servo would draw more power to maintain the directed position.

Best way to detect such an issue is probably on the bench. Disconnect the pitch links from the blade holders and then pull outward on each holder and try rotating it. If you notice any significant detents or sticking at any point then you may have an issue. Clean, relube and try again. If it persists, time to replace.

 

[callsign4223]

I think the reason you don't notice unsmooth (scientific term ) bearings in the head is because you are looking at a partial rotation versus a full rotation like on the main shaft/torque tube. The actual rotational change is very small. Even when the tail needs work, it's generally not bearings causing the issue, something is binding.

 

[Tony]

Worn thrust bearings can cause vibration issues if they have worn past holding tight. This will cause slop in the grips and allow the grips to move in and out. But, this is rare, however if you feel any pitting or notchiness (yeah, I said it!), then it's time to replace them.

 

[murankar]

I was told a lack of grease can cause a vibration. I had some vibes and then I repacked the thrusts and the vibes toned down a bit. So I would check the grease in the bearing and see if they are packed well.

 

[coolgabsi]

I was told a lack of grease can cause a vibration. I had some vibes and then I repacked the thrusts and the vibes toned down a bit. So I would check the grease in the bearing and see if they are packed well.

Lack of and use of wrong grease can cause vibration

That applies to all birds

The dampeners need the right grease on them (silicon grease from a plumbing store) to make sure they are smooth and don't have a VICE grip on the feathering shaft. In flight the whole system centers out itself. If your bearings are not packed and dampeners are holding on to the shaft under load with a death grip that's just asking for imbalance .. As the blades can be upto 1mm off in flying radius.

When I say right grease.. For all people not familiar with the fact this a hydrocarbon based oil or grease will or can make your dampeners swell up. Swollen up new dampener is add bad if not worse as a used up broken or worn out one. So
No bearing oils no oils in general. SILICON GREASE .

Thrust bearings should be packed with good lithium based grease (I think) I just got thunder tiger thrust bearing grease .. Black stuff


Yes thrust bearings can cause vibrations if they are rubbing up on the shaft, or have a ball out or something failed of have rusted and again are causing a horizontals bind in the system

Nope they don't need replacement every 20-25 flights. They need packing when installing and cleaning when repairing and replacing till you feel like they need replacement .

Last two and a half years on my 450 I replaced them once.. That too cause I lost the covering of one side for one

As far as installation.. Make sure to follow the Manual on what ID goes where.. Big inside or small outside.

My tracx head is small ID in towards the head yoke

I think align asks for small ID out... So yeah the head .. The part that makes you fly.. Needs to be built meticulously and greased and lubed ..


BUT

If it ain't broke don't fix it!

Fly safe!! have fun!

 

[murankar]

I used silicone grease on mine. I also used the same grease on the dampeners.

 

[helicc16]

Thank you all for the insights. I didn't know it's so important to lube up the feathering shaft. I just do it because the instructions say so. I do have a helicopter with head vibrations. And I am suspecting the thrust bearings. Wil tear down the head and update you guys on this.

It takes lots of unselfishness to sit down to type and share your knowledge with fellow enthusiasts. That's what I appreciate most about this forum.

Man, I feel smarter by the day being with you guys