Big loop = problem

[miketrex450]

Hey guys, just got my first Goblin 500 ( used ).
Was out flying today and everything was working great ( have 4 flights on it ) when I decided to do a big loop, after I came out of the loop the tail started to act funny so I tried to bring it back in and it started getting worse to where it was slowly pirouetting and I got it down safe. Anyways I started looking it over and found that the slider on the tail shaft was basically locked in place ( wouldn't slide ) so I took all linkages off from it and it still wouldn't move until I forced it, then it broke loose and applied some oil and it seems to be fine now.

What would cause this and what do I need to do to prevent it from happening again ???

[jrman83]

Cold temp with excessive lubricant?

[miketrex450]

It is 55° here today and I didn't even put lubricant on it since I got it .

[Coco66]

Slightly bent tail shaft.

[ticedoff8]

The problem with electric helis is they are not self-lubricating.
With nitro, the oil coats everything on every flight.

So, if you are flying an electric heli (like a G500), you need to oil things periodically.
Like the tail pitch slider.

You should also oil the swash's omni-bearing and main shaft where it slides.
Oil / grease the thrust and radial bearings on the various blade grips
Oil the motor's bearings
Etc, etc, etc.

In general: If it moves, slides or rotates, oil or grease it periodically.

But, you should also look at your flybarless controller's log the vibration log to see if the tail rotor has excess vibrations - that would indicate a TR drive shaft that is bent. But, unless you smacked the tail on the previous landing, that would typically not cause a gradual lock-up of the pitch slider.

[Coco66]

Well, oiling and lubricating is - and will always be - a big battle between the ones who do and the ones who don't. We should not enter that battlefield once more.

Still voting for the bent tail shaft - used heli, you never know what it went through before you got it.

[PilotPin]

Was there any scratches on the shaft. Might have got a little stone jammed in between the shaft and slider . Had it happen on a airplane nitro motor . Got in the throttle barrel locked it up tighter than the devil .

[miketrex450]

Will have to take a closer look but I don't think there's enough space to fit even the tiniest of stones, it seems like the tolerances on the Goblins are pretty tight.

[grasshopper2]

The only time that has happened to me is when there is old and mucky lubricant on the shaft, although it didn't lock completely the servo had a hard time moving it, and it was very stiff when moving by hand. I put some runny oil on it and cleaned it off, moved freely again.

[miketrex450]

So are the tolerances that much tighter on these Goblins that you have to make sure you oil often ? I am used to the Align Heli's and I did oil often but didn't ever seem to be an issue if you didn't for awhile

[GREYEAGLE]

In the most humble opinion : It's a good old friction weld between the steel tail rotor shaft and the brass tube bearing slider. Lack of friction protection.

Pretty easy to examine and proof it too. Use a Bright Mag lite.

Take it apart and look down inside the brass or bronze bearing slider. It will leave evidence to prove it.

If you see a miniature skid mark { Galling } in the tube - the temp exceeded the melting point of bronze.
It started to fuse it self together.

If you see a miniature divot and a little nugget of something stuck : That is a spall.

Because it is a brass or bronze bearing on steel, their is actually a better lubricant than oil which will attract abrasive dirt in the operating environment. That promotes further wear.

What do you see down in their ??

[miketrex450]

I will have to take it apart tomorrow and check it out. So your saying if it wasn't lubed ( dry) the friction could have cause a "weld " I guess that makes sense

[cool cat]

Maybe no gov on the motor? I sometimes, more like lots of the time, stall a bit at the bottom of a big loop. Makes the tail piro for a 1-2 second and acts like it wants to drop.

I am going to try an use my FBL gov and see what a difference it will make.

Otherwise it's good collective management training..lol

[Coco66]

Originally Posted by cool cat

Maybe no gov on the motor? I sometimes, more like lots of the time, stall a bit at the bottom of a big loop. Makes the tail piro for a 1-2 second and acts like it wants to drop

The OP clearly stated that the tail slider was stuck - does not fit your ipothesis, Watson...

[Snakebite]

Originally Posted by GREYEAGLE

Because it is a brass or bronze bearing on steel, their is actually a better lubricant than oil which will attract abrasive dirt in the operating environment. That promotes further wear.

I hate to be the Grammar Nazi, but is part of that sentence missing?
Brass and steel should work as a natural lubricant, no oiling needed...

Edit/
Oh, I've got it, should have been 'this' rather than 'their', sorry, I've been awake all night... lol.

[cool cat]

Originally Posted by Coco66

The OP clearly stated that the tail slider was stuck - does not fit your ipothesis, Watson...

The tail action I described could have caused or added to the situation described.

Just trying to be helpful Holmes

[miketrex450]

Well this kinda sucks, a few guesses but nothing solid to go on, apparently nobody else has had this happen ? I don't know weather to fly it again or not ?

[miketrex450]

Here is a pic of the spot where it was stuck, it appears to be a copper color there so maybe it was heat ?

[KiloXray]

Check the inner groove of the ring that the slider "fork" rests in. If at some point that heli had a nasty vibration it is possible to have worn grooves in there that the fork tips can catch on.

If that is the case, it's not really the "sliding on the shaft" that is sticking, so much as the fork tips getting stuck.

At least it's one more thing to check. Spitballing here.

[KiloXray]

Also, check the shaft and the inner diameter of the slider for galling. Even the smallest little bit can be problematic.