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bearing maintenance

Tom Martin

Well Known Member
There are two bearings that hold the main front sticks in the RV14 and the following picture shows one of them.

9kt7qx.jpg


This is a well designed item that captures a COM3-5 bearing between the two pieces of metal, much the same way as the aileron hinge brackets.
There are 8 -3 rivets that hold the bearing in place and another 8 -4 rivets that hold the bracket to the small bulkhead that is forward of the main spar. There are two dash 8 screws that also go through the bulkhead and tie into a stiffener on the other side.
Although I have yet to install any controls I am sure that this item incorporates the "stops" for stick travel in the upper and lower bumps.

This is a well thought out, light and strong unit.
The problem comes with long term maintenance. This is going to one very difficult bearing to replace, 16 rivets to drill out in a pretty tight space. I know that these bearings are very reliable put eventually it will have to be changed out, 10 or even thirty years down the road.
I am all for building light, but in this case I believe it would be prudent for the engineers to take a second look at this bracket and add some extra screws, or bolts so that the unit can be removed without drilling and riveting. It would turn a two day job into a couple of easy hours.

This is not a big deal, build on, but take a look at it yourself and imagine the repair, it will not be pretty.
I have been building and maintaining RVs and rockets for over 20 years and stuff does wear out. You will be a surprised when your brand new airplane turns 10 years old!
 
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I don't mean to imply I think they will last forever, but the same bearing, in the same type of application is still going strong in the Blue RV-6A prototype at 26 years old with no sign of trouble.
They are in a well protected area, and if lubed (as they should be) once a year, it seems they will last a very long time.

BTW, I caution anyone making a change to this bracket without doing some detailed engineering.... As you mentioned, it is a control stop for the stick travel in the pitch control circuit. With the length of the stick, factored against the design load required to meet FAR 23 The loads they know an average pilot can easily exert), the loads this bracket / rib needs to be able to take are quite high. Hence, the reason there is more than just a couple screws used to mount it.
 
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I don't mean to imply I think they will last forever, but the same bearing, in the same type of application is still going strong in the Blue RV-6A prototype at 26 years old with no sign of trouble.
They are in a well protected area, and if lubed (as they should be) once a year, it seems they will last a very long time.

Scott, what is your lubricant of choice in these bearing?

Thanks,
 
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