Bushings were spinning in the casting…

[Diana]

That’s how my mechanic just described what he found in the Citabria as he was fixing the problem of way too much play (slop) in the front stick. I would like to be able to visualize just what that (bushings spinning in the casting) looks like. Googling (sp?) didn’t help me find a description or pictures. Do you all have any suggestions? My parts manual is at his shop, and I can’t find any pictures of that particular area.

Thanks!

 

[gkainz]

I'm imagining that would that be the same as a "spun bearing". Lots of google hits on that but I'll bet no pics. A spun bearing is when the bearing race (the outer part) turns against the casting that is supposed to hold it tight. I would imagine a bushing spinning in its casting is similar - the bushing spins, rather than staying stable and the rod/cable/whatever turns within the bushing. Wears out the casting where the bushing is pressed in and causes slop. Not an A&P, just grew up where "if you want if fixed, you fix it yourself"

 

[Skip Miller]

Greg has got it. From Wikipedia "Mechanical bushings are cylindrical linings to reduce friction and wear, or constrict and restrain motion of mechanical parts. Plain bearings are similar."

Instead of the stick's "axle" turning in the bushing, it is frozen to the bushing and the whole bushing is turning in its support. As the surfaces that are turning against each other are not designed for that, there is high wear at that location.

-Skip

 

[Ken Ibold]

That’s how my mechanic just described what he found in the Citabria as he was fixing the problem of way too much play (slop) in the front stick. I would like to be able to visualize just what that (bushings spinning in the casting) looks like. Googling (sp?) didn’t help me find a description or pictures. Do you all have any suggestions? My parts manual is at his shop, and I can’t find any pictures of that particular area.

Thanks!

Hmmm, way too much play in the front stick, and difficulty with maneuvers that require lots of forward stick. Coincidence? Surely not!!!

 

[Steve]

usually the result of inadequate lubrication...

 

[Diana]

Greg has got it. From Wikipedia "Mechanical bushings are cylindrical linings to reduce friction and wear, or constrict and restrain motion of mechanical parts. Plain bearings are similar."

-Skip

Thanks guys! I still can't seem to get a picture in my mind of how it would move around in there, and how it would move differently after wearing down.

 

[Diana]

Hmmm, way too much play in the front stick, and difficulty with maneuvers that require lots of forward stick. Coincidence? Surely not!!!

I would like to blame it for ALL my imperfect maneuvers. I did notice how much easier and cleaner my aerobatics were in Chip's Citabria with a nice solid feel to the stick.

 

[Diana]

usually the result of inadequate lubrication...

Is that a place that is routinely lubricated? It's kinda hard to get inside that joint.

 

[Steve]

I don't have a diagram of the pivot point, or a copy of the service manual, but I would imagine that it requires some type of grease on a routine basis if it is not easily accessible for inspection and oiling.

I'm not a certfied aircraft technician but I've been told I am certifiable...

Is that a place that is routinely lubricated? It's kinda hard to get inside that joint.

 

[rmciottijr]

Diana,

If you look at the door hinge on you car/truck most have bushings. It is little brass ring (might be covered with grease) that is pressed into both sides of the hinge. A nail like bar slides through them holding the hinges together. Like Greg said the bushing spins, rather than staying stable in the hinge. This is not exactly like a linkage bushing but it will give you an idea what it looks like. I attached some pictures but I don't think they will show if not, google Linkage bushings and click on images or try this link http://images.google.com/images?hl=en&q=linkage%20bushings&sa=N&tab=wi Some bushing are plastic but do the same thing.

Bob

 

[Ed Guthrie]

Diane, a common example you may have seen would be something around the house such as a cabinet door pivot. The pivot is steel and it turns inside a wood hole. If the pivot point was allowed to pivot directly on the wood it would wear the hole rather quickly, so a piece of plastic or metal with a concentric hole is pressed into the wood hole in the cabinet (this piece is a bushing). Now the pivot can turn inside the plastic piece while the press fit holds the plastic still within the wood. Analagous to your bushing problem, the metal pivot rusted or whatever inside the plastic bushing, "froze" in place, and under the torque load the bushing started turning inside the wood. Now the bushing is wearing against the wood.

Then again, maybe you've never noticed such a thing and my example was worthless.

BTW, did you receive the releasable tie-wraps yet?

 

[acrodisiac]

The bushing is thick metal disc about 3/4" in diameter and about 3/4" thick with a bolt hole through the centre.The bushing fits in an equal size hole in the control link that joins the the front and rear stick.
The control stick socket is a cast fork that straddles the bushing and the control link. (the stick , front or back fits into the socket like the handle of a two tined fork -aka yoke). A bolt passes through the fork the bushing and the control link to hold them together. THe bolt forms the axle that permits stick movement fore and aft - elevator. In side to side movement for aileron the axle acts as a "lever" to cause the control link to rotate . THere are two wear directions happening. Fore/aft is purely rotational wear from the bolt turning in the bushing hole that it passes through. Side movement creates a wobble or rocking type wear. THis occurs from the axle rocking in the bushing hole AND the bushing rocking in the control link hole AND yoke holes. You will likely notice this wear in the side to side play of the stick. Fore and aft wear is not so easy to feel and really is not the significant wear mode (unless the bolt is seized and causes the bushing to rotate in the bore).
THe bushing can be lubricated with a spray lubricant after lifting the control stick boots. Lubrication will ease the fore aft movement but it will do very little to mitigate or prevent the side to side rocking wear.

THe bushing is cheap and easily replaced however if the wear has been transfered to the control link bore and or the stick yoke then not easy and not cheap is the word. Tightening the through bolt will often remove the slop but this is a finite repair method. Wear will always eventually stack up until new parts are required to resolve it. If the bushing seizes up within the yoke or control rod then wear will be rapid and the repair expensive.

I've changed my front stick bushing twice in 1200 hrs and have tightened it a few times (Decathlon). The dimensions stated above are all from memory and are approximate so please don't nit pick ; it's the general layout ,operation and servicing that I'm trying to illustrate.