Elevator trim tube lubrication

[rv8bldr]

Hi folks

During my recent pre-cover inspection, the inspector tagged me with a deviation/observation that there was no provision to lubricate the outside rotation point of the elevator trim tube during annual inspection.




I know there are no mentions of this on the plans or, as far as I know, in the Bearhawk book. Have any of you dealt with this before? If so, how did you approach it? If not, what has been your experience. I think I can explain this away if there is a history of positive service of this part without adding the provision for lubrication.

Thanks in advance.

[alaskabearhawk]

I modified my trim system to run with a cable, but before I did I thought about that issue. I have profiled ribs and theoretically I could access all the bearing surfaces through a lightening hole in the outside rib. However that would probably require the removal of the horizontal stab for access.

This is an excerpt from October 1997 BearTracks. I don't know if this helps your situation or not:

Bob, I have a few questions you may be able to answer before you head for Oshkosh:
3) How do you access the trim shaft bearings in the tailplane for lubrication after the fabric is on?
Regards - Ray Thurston #005 - NEW ZEALAND
Ray

I am starting to get a lot of questions about the fuselage now. I assume lot of the builders are done with their wings and tail feathers and are starting on the fuselages. Regarding your questions
3) No access on the prototype, shafts and bushings. I epoxy painted and greased on assembly. No problems to date.
Thanks for your questions and keep in touch. ~Bob

[rv8bldr]

Thanks, Paul. Not a great deal of help in that comment from Bob :-)

[Steve W]

image.jpg
I drilled a small hole through the underside of the bushings and bronzed a nut on with the appropriate threads for a grease nipple. On the rib flange I drilled and bronzed a support washer with the hole in line with the nut. These long nipples will be out beyond the fabric enough to get the end of the gun on. You might have to get what ever fits. Not sure of the length as I had a bunch of the nipples layin around. I also drilled and welded a washer to the elevator and rudder hinges. Tapped and put in a short nipple. Careful with the thinness of the threaded area as its easy to bottom out the nipple on the male tube. Also small effort with the amount of grease. Just a minute squeeze of the gun is enough. Picture of the hinge when I broke a wire. Older thread somewhere from 2020.

[rv8bldr]

Thanks, Steve, but I am talking about the TRIM tube, not the regular hinges. I did exactly as you have done for the hinges, but the outboard end of the elevator trim tube is buried in the HStab and covered so there is currently no way to get at it.

[svyolo]

I will look at the plans tomorrow, but I think you can lube tube by unbolting both the inboard and outboard horns and sliding the tube outboard and inboard. I just assembled my tail for flight and I am pretty sure that is what I did.

[rv8bldr]

Did you put an access port in your HStab covering so you can put some lube in there? I am talking about the outboard end of each trim tube which is, according to the plans, fully covered so not directly accessible.

[Steve W]

You totally missed on the first part of my message.
I drilled a small hole in the bottom of the trim bushings that are welded to the stabilizer rib on the bottom side of the stab. Bronzed the nut, supporting washer and used the long nipples to protrude out beyond the fabric. 2 each side. I’ve lost most of my construction photos.

[rv8bldr]

Apparently I'm easily confused :-) I read the message, then commented on the pic. Whoops. Thanks, Steve. I'm ready for cover on the HStab, but I think I will copy you while I still have access. I was already going heading to the parts store this morning for something else so I will add the longer Zerk fittings to my list

[Rob]

[Steve W]

I laughed when I saw the picture. Yea that’s an old one I no longer had on my phone that you can see the nipples for the bushings.
Steve

[rv8bldr]

Perfect! Thanks Rob (and Steve)