Trim screws.

[PA1195]

Locally many mechanics use Shell #5 or 7 or Mobil SHC 100 grease products. But that assumes periodic inspection and maintenance. With these trim screws other than the oil hole on the input shaft the remainder may not be serviced. Maybe it's not an issue. I don't know but if replacements are needed then that implies wear which to me indicates the need for at least initial servicing.

Tim mentioned he likes oil. Grease is simply oil with additives like thickeners and anti-wear anti-oxidation agents (https://www.stle.org/images/pdf/STLE...ec15%20TLT.pdf). It tends to stick around longer than plain oil when exposed to the elements, pressure, and wear. But eventually the oil can separate from the thickener and run away leaving only the additives to lube the parts.

Anti-seize is also a thickened oil base with additives, but mainly used in high temp situations when galling from metal contact or freezing up of the components can occur. It's tough stuff but not suggested for continuous movement like wheel bearings for example.

I'm not an expert on which is best and maybe Hank can carry this further and reach a conclusion. One common early compromise was the infusion of oil with graphite and that was often recommended as a control lube for aircraft. Spray dry film lubes containing Moly are also available and function well in auto and semi-auto firearms at all temps in my experience.

I think one thing that should be done is to subject the unlubed screws to below 0F cold (put them in a freezer?) and see if they function without excessive friction.

Gary

[PA1195]

I guess I should ask: When worn what part(s) and where?

Gary

[astjp2]

I stopped using aeroshell because it breaks down and the oils separate out. Cessna calls out aeroshell 33.

[Hank Jarrett]

The major wear I have seen is in the bell-crank bolt and hole allowing the crank to wobble, the pushrod ends to the bell crank itself and tab arm and axially from thread wear. The worst slop in the trim system I found was from the entire threaded assembly and pulley not being properly shimmed allowing the whole assembly to shift side to side. I did a LOT of rebuilding of mine trying to get all the slop out only to find that a missing washer between the pulley and airframe caused more slop than all the rest combined. Another source of trim slop was worn hinge attachment for the trim tab itself (my 41 has a metal rectangular tab with screws attaching it to the elevator and the 45 has a wood tab with a wire through the leading edge into tubes welded to the elevator cove). When you rework the trim system in the tail ALL of these need to be addressed. It is nice to be able to wiggle the tab and have it NOT move. Of course if your threaded shaft and barrel are either seizing or sloppy the only way to fix it is going to be a new assembly. This addendum to the replacement assembly discussion is really to make sure the replacements will last longer than any of us. I see no reason they shouldn't with a good lube seeing how long the old ones lasted.

[PA1195]

Thanks Hank for the wear patterns. The previous owner of my '41 replaced some parts and recovered the elevator. I do see some of that side to side shifting in the pulley-trim screw through the *elevator* mounting and will look for that clearance washer. I had thought an O-ring or fiber washer might also work mainly as an oil-elements seal.

So does the threaded portion of trim screw actually wear out internally, and how about the shaft inside the steel aileron tube that has the oil hole?

Maybe there should be an inspection ring on the lower *elevator* near the parts to deal with these matters. Easy to do during or after fabric covering.

Gary

[Hank Jarrett]

Gary, I am missing something. This is the ELEVATOR trim system. Do you have an aileron trim system? I have never seen that. The metal washer between the threaded shaft/barrel assembly and the airframe is to keep the threaded parts from moving sideways (which would move the bellcrank and trim tab just like screwing the trim screw would. The washer isn't for holding lube, it si for taking up the slack in the assembly. The threads can wear inside the shaft/barrel assembly or you can get contamination in the threads that will make it hard to turn them out and together which will make the cable slip.
On my 41 I have an access cover on top and below the bellcrank and threaded shaft so I can get in and inspect it on annuals. I can have someone turn the trim crank from stop to stop while watching the parts to look for wear or slop.
There seems to be a "rule" among the A&Ps I have talked to that the round inspection covers are only supposed to be on the bottom of the wings and tail. The top surfaces require covers held on with screws. I don't know where they heard that (anyone?) but it is wrong. The snap on round covers should only be used on the high pressure side of surfaces and screws are used for the low pressure side OR high pressure side. The BOTTOM of the horizontal tail is the low pressure surface, NOT the top (except when the elevator is deflected down). Horizontal tails normally lift DOWN, not up. My 41 had a round cover on the bottom when I bought her and I put a square one with screws on top. I plan to put a screw type square on BOTH sides, if for no other reason than to avoid having to argue with A&Ps.

Hank

I really doubt there is enough pressure difference on a Taylorcraft elevator to make a difference, but if a screw retained cover can be used on either side, why not do it.

[PA1195]

Good catch Hank I had written aileron when I meant elevator. My I-Mac can do that if I enter the wrong letters as it expects a correct word to follow.

The O-ring next to the rear trim pulley might serve a multi-function by excluding debris, retaining lube from the oil hole that can get on the pulley and cable, and minimizing axial runout.

I'm going to have my mechanic consider adding a lower inspection cover of his choice on the left elevator below the trim's components. That way it can be inspected and maintained as required.

Thanks for the feedback,

Gary

[Robert Lees]

[PA1195]

Excellent Rob I'll burn a copy and offer to my mech for his consideration. That would make maintenance easy. Mine has some hardware slop as well.

Gary

[Robert Lees]

Lubing trim screw with a gob of grease:



Gary, have a look at

https://www.taylorcraft.org.uk/OtherRestorationPhotos-new.htm

and

https://www.taylorcraft.org.uk/Brey_rebuild-Tailfeathers-gear-legs.htm

[Hank Jarrett]

Love pipe cleaners, just don't forget and clean your pipe with it after using it on the Taylorcraft! I bet it would get anyone to quit the pipe in short order. ;-)

Hank

[PA1195]

Pipe cleaners make good pitot tube cleaners. I carry one to remove bugs water and ice (when melted by hand pressure on the tube).

Thanks Rob for the link to trim parts. Only a rebuilder would know what mystery awaits under the covers.

Gary

[Scott]

I suspect most of the wear on the bolts/pins, pushrod, belcrank and control horn is due to vibration more than movement of the trim system. For this reason a "sticky" lube that will keep the parts from fretting against each other is a good idea. I like EZTurn. It goes on sticky and stays sticky! A pain in that it gets your tools and hands sticky as well, but it works. I used to maintain a Grumman Goose and everything was assembled with EZturn, which meant even after saltwater ops it was easy to remove screws etc.

For the jack screw I use a molybdenum disulfide lube of the kind normally used in auto CV joints, just make sure it has a low enough working temperature eg -30C.

Many greases, surprisingly, are good at pulling moisture out of the air. Clearly this is not desirable. Synthetics are better from this perspective.

[Hank Jarrett]

We used a lot of Molly-B in the Navy. Used to HATE that stuff. If it got on your cloths it really ruined them (and anything you washed WITH the contaminated cloths). It is a grease with Molybdenum flakes embedded in it and the flakes flatten out under pressure and don't allow the grease to squeeze out. We used it on all the high bearing load pins and joints like in the arresting gear where if the grease was pushed out the parts would gall. One thing we discovered was that Molly-B when combined with salt water and stack gasses (from the ships boilers) became highly corrosive. We thought it was going to become a bigger problem than it did. When all the carriers went nuke the problem went away (well, except for the ruined cloths). I never did have a chance to find out what was in stack gasses that wasn't in jet exhaust. Problem gone and so was the research funding. Doubt many of us need to worry about stack gasses and salt water, but i DO have a hook on the tail of my 41 T!

[n6346m]

Rob,
What kind of covers did you eventually put in? When my Stinson was recovered, they put the inspection cover too close to where a rib and spar meet and the usual covers that are available are very difficult to remove and install. Since you have to slide the retaining spring tab way-in past the edge of the hole in order to get the other end of the tab through the opening, it turned out to make a mess out of the opening after all these years of fighting it.

Bob Picard