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Building Tips and technical articles. => Building techniques => Topic started by: Brett Buck on June 21, 2011, 10:22:32 PM
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Here is a kwik-link I removed from my airplane. It was on the rudder adjustment, and was new about 300 flights ago. Now the pin has worn about a third of the way through. The bearing surface in the horn is *plywood* and the entire thing gets inundated with oil, and of course there is essentially no load on it aside from very mild vibration.
There's no way that this would last any length of time in a regular control hookup.
Brett
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Pretty much makes a strong case doesnt it Brett!
great picture, thanks
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As a sidebar to this, I spoke with Tom Morris recently. He now recommends titanium inserts for use with ball links. Apparently there is evidence that a steel insert on a CL Stunt ship failed.
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Hi Brett,
Yes, it has long been established that traditional quick links are a non starter for the actual control system. But for non critical static trim functions like your rudder or trim tab adjusters they do quite well. Like with anything else in our setups, items need to be inspected on a regular basis. Lines, Line wraps, Handle hardware, engine bolts, wheel keepers, etc.
BTW, Material engineering wise anywhere a Steel component fails a Titainium component will also fail. Othere than being lighter, corosion resistant, and non magnetic, titainium does not have strength advantages over steel. The failure most likely was caused by a defect in the part, or damage caused by over tightening the attachment leading to a stress fracture. So if you have weight issues, or need the "Ooooh Titainium, cool factor", it does not merit the additional expense of going titainium.
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Yes, it has long been established that traditional quick links are a non starter for the actual control system. But for non critical static trim functions like your rudder or trim tab adjusters they do quite well.
I would not refer to the above wear (in maybe 400 flights) as "doing quite well". The plywood horn did better.
Brett
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I would not refer to the above wear (in maybe 400 flights) as "doing quite well". The plywood horn did better.
Brett
So what will you use instead? That will weigh the same and be as simple and trouble free to adjust? Now while I am a great fan of low friction controls. The Vector Kit I built a while back had sealed ball bearings for the Bellcrank Pivot, Control horn holes, and leadout wire bellcrank connections. You could blow on the flaps and elevators and they would freely move. It was a case of extreme over engineering although there was zero control input resistance at the handle.
BTW they make really small light weight sealed bearings for use in dental instruments, which is what I used.
I probably wount go that route again, it really was not worth all the extra effort and expense. But if that wear and tear over 400 flights still bugs you, just epoxy a little brass or copper bushing into the plywood and viola the wear problem goes away.
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So what will you use instead? That will weigh the same and be as simple and trouble free to adjust? y.
I am using the same again for now. When I get a chance I will replace it with a bent wire and keeper.
Brett
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Brett, if the plywood wore out the steel pin in the Kwik-link, why would you expect a piece of bent steel wire and a keeper to be any better? Wear out the steel pin, wear out the steel wire: seems like six of one and a half dozen of the other.
IMHO, the right answer is to brass-bush the plywood as mentioned above.
Bill
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That must be a heck of a hard peice of plywood to wear that steel pin out. Never heard of that one before. Learn something new everyday. H^^
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Actually the clevis in a nylon horn would not have worn. Plywood and metal horns are slow death to a clevis.
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My guess is that the steel pin in the clevis is very soft and cheap steel. Stainless steel would not have worn like that, and neither would piano wire.
A general rule for pin/bushing situations is to have one hard and the other soft. You'd think steel/plywood is ok.
I wonder if Howard has had any such issues with his CF flap actuator horns, and if he has, can he write a poem about it that doesn't include the JCT? LL~ Steve
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I'm building a !/2-A stunter. Using a Kwik-Link for elevator. The horn is G-10 epoxy-glass. I will expect a failure after 300 flights. (In Oregon, it takes 19 years to manage 300 flights).
Floyd
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Brett, if the plywood wore out the steel pin in the Kwik-link, why would you expect a piece of bent steel wire and a keeper to be any better? Wear out the steel pin, wear out the steel wire: seems like six of one and a half dozen of the other.
IMHO, the right answer is to brass-bush the plywood as mentioned above.
Bill
Kind of what I was thinking, Oh Mr. Bill if I forgot at the time, I wish to thank you for cutting to proper length and wrapping the ends of my control lines back in 1994 or there about at flushing meadow park!
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That must be a heck of a hard peice of plywood to wear that steel pin out. Never heard of that one before. Learn something new everyday. H^^
It's the glue in the plywood. LL~ LL~ LL~ LL~
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Hi Brett, I'm at Delaney's house and saw your thread. On my '87 Tempest ( Tigre .46 powered 57" span open model) I used a quick link but, inserted a small piece of brass tubing on the quick link shaft. the elevator horn was made of steel. The model had about 500 flights on it and only changed the piece of brass tubing once which was a snap to do.The thread that the quick link threads on to must be a snug fit. I never had any other problems.
Hope this will help someone,
Bart
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Hi.
I've had a similar experience several years ago. Actually, my model had a similar Sullivan 4-40 quick link for both rudder adjustment and at stab horn. They both had a brass sleeve in the horn. I remember that the rudder link wore out after a few hundred flights but there was never any problems with the link in the stab horn.
The answer is quite simple: Oil and dust together make a grinding compound that gets embedded in the softer part of the sliding pair (plywood or brass) and it wears out the harder metal. There was no abrasive dust inside the fuselage, thus no wear.
I allmost daily lap and polish hardened steel parts with diamond paste and tools made from tin, zinc or iron.
Lauri
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Hi Brett,
Yes, it has long been established that traditional quick links are a non starter for the actual control system. But for non critical static trim functions like your rudder or trim tab adjusters they do quite well. Like with anything else in our setups, items need to be inspected on a regular basis. Lines, Line wraps, Handle hardware, engine bolts, wheel keepers, etc.
BTW, Material engineering wise anywhere a Steel component fails a Titainium component will also fail. Othere than being lighter, corosion resistant, and non magnetic, titainium does not have strength advantages over steel. The failure most likely was caused by a defect in the part, or damage caused by over tightening the attachment leading to a stress fracture. So if you have weight issues, or need the "Ooooh Titainium, cool factor", it does not merit the additional expense of going titainium.
Agree...Here's a Titanium bolt from a wing trailing edge cove panel on a Boeing 737-800, inline with the engine strut/ exhaust. (high vibration area) It's a 3/16" clevis bolt that was written up for "excess play". The other bolt is one of those 1 in a million that went through production and never got the hex stamped - notice the head markings and cotter pin hole, lol. I don't own a wrench for that one.
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I was surprized when I had a titanium end fitting break; I had used a jam nut to prevent vibration of the threaded link and the link broke "inside" the jam nut..... ???
Jim
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Ti is really sensitive to contaminations from other metals. Lead for sure. Maybe copper/brass/bronze also, but don't quote me on that. H^^ Steve
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Ti is really sensitive to contaminations from other metals. Lead for sure. Maybe copper/brass/bronze also, but don't quote me on that. H^^ Steve
Depends on what grade, but yes. I wasn't aware of lead being an issue but for sure, cadmium (like cad-plated tools). Doesn't like anything with chlorine, either.
Brett
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There may be some Cadmium plated fasteners, but not normal tools. Most fasteners will be zinc plated with a chem treatment. I was thinkin' that it might be a chromed brass nut that caused the trouble, but I can't recall for sure that copper/brass/bronze is a problem with Ti. Also, I don't think I've seen more than two Ti alloys, and don't remember the alloyed metals or ratios.
In '81, Boeing took our lead hammers away. Somebody had used one to whack a Ti nut or pin or something while installing it on a plane, and the part failed as a result. Seems to me it was a landing gear part on a 747. I guess a little CSI work paid off. :-X Steve
Edit: Ti-Al-Va....Titanium Aluminum and Vanadium. The only alloy I've seen is 6AL-4V. This website is useful. Google will find more useful stuff. http://en.wikipedia.org/wiki/List_of_alloys (http://en.wikipedia.org/wiki/List_of_alloys)