Lithium Grease University

[edwalker]

I don't know if any of you have been having this issue, but I finally solved a problem that has been vexing me for over a year. I found that the smoothness with which I can install and disassemble the wingtips varies tremendously. This was really frustrating. Some days the wingtips were easy to assemble, other times it was remarkably difficult to get them seated properly or removed at the end of the flight. At first I thought it was a temperature related issue, but having explored various approaches over the past year I think I now understand the problem. The mistake I was making at first was not using the lithium grease frequently enough, followed by a period where I was using too much, too often, and it was only after I actually understood the component elements of lithium grease that I figured out what was wrong.

Lithium grease is actually a soap. Unlike hand soap, where sodium or potassium is combined with fatty acids, lithium is used since it is less likely to corrode the metal. This soap is then blended with some form of oil. The reason this is important to know is that after disassembly the exposed parts are subject to drying as the oil evaporates, leaving a soap scum on the metal fittings. If you have ever cleaned the shower or tub you know how difficult soap scum can be to remove. This residual deposit is very difficult to see and so the attachment fittings look just a bit dull, as if they just need more lithium grease, when in fact there is an accumulating, uneven layer of dried soap gradually decreasing the clearance between the pin and the bushing. You can actually use your fingernail to scratch the residue and see what I mean. Once the soap has dried additional lubricant does not make the deposit soluble, and only a gentle polishing will take it off.

What finally worked for me was to get some scotch bright pads and cut them into half-inch wide strips. These strips can be used to buff the pins and can be inserted into the bushings and rotated. This should be done with some fresh lithium grease so that you can use the oil as a lubricant. It's pretty effective in removing the soap scum, and now the addition of a small amount of lithium grease prior to assembly seems to restore the ease with which the components come together and disassemble. Also note that this scum can fill the corner where the pin body meets the wing rib and can round out this right angle preventing the seating of the pin against the bushing. You’ll know this is a problem if the spar pin seems tight and resistant.

Another thing I’ve noticed is that in cleaning the bushings one often gets a green copper oxide residue on the rag, suggesting some oxidation. Although applying fresh lithium grease after flight might inhibit this, the problem is that it will just dry out. Next week I’m going to try some half inch rubber stoppers to plug the bushings and some drilled out larger stoppers to cover the pins to decrease the area subject to evaporation.

[Eric Greenwell]

Does this affect both the long and short tips? My long tips have always gone on/off easily, and I grease them no more often than every 10th or 20th time with whatever is handy. I don't use lithium grease, simply because there is none at the hangar.

I have used a lithium grease on the main pins (1.25" pins that slide through the spar stubs, one on each side of the fuselage, that take all the bending forces) for my ASH 26 E self-launcher, and it works well, but so does 30 wt motor oil, the thickish grease the factory supplied, and motorcycle chain lube. Some oils are slipperier that others, with the chain lube being the slipperiest. I clean and grease the pins every 15-20 assemblies, no greasing in between.

My short tips are easy enough to install, but more difficult to remove. The pins seem to bind a bit, as if the pin spacing is slightly too much or too little (the long tip pins might be the same, but the long tips offer so much leverage, I can't tell). I put screwdriver blade in the slot between the tip and wing, near the front, twist it gently so it pushes the tip out slightly, and that's enough to get it started. A bit of wiggling and it comes off.