Stuka Stunt Main Forum · 27 of 27 known posts recovered
Tnx, Mike, the "Old Harley Man" [email protected]
"As a young man I started with nothing and still have most of it"
They're available from www.tomsbuildingservice.biz and www.windyurtnowski.com and probably other "cottage" C/L shops.
If you have a profile fuselage, or the full fuselage is wide enough, you can use an R/C Ball Link, instead. This usually requires at least 3/4" of unobstructed access. For the adjustability factor (only), I'm trying a 4-40 Hangar9 unit on my CardinalARF. I've heard that the Rocket City units are better, but can't /haven't found a source.
As to necessity, it depends on how long you expect the plane to live. If it's gonna die in 100 flights, bushing is probably unnecessary. If you expect it to fly 500 flights or more, bushing the linkages and, more importantly, the leadouts (cable) is almost mandatory. At least, that's what I think.
Ralph Wenzel
Tnx, Mike, the "Old Harley Man" [email protected]
"As a young man I started with nothing and still have most of it"
My view is to make it as good as you can, 'cause you never know how long a model might last. Even more important, you never know who's going to be in the way when the controls fail...we don't need that!
Legend has it that Tom Morris has some kind of exclusive franchise on the Rocket City rod ends. I guess I don't need to provide the link, huh? 
Steve
As mentioned above, can't find Rocket City stuff.
I'm planning to put a Dubro 2-56 ball link on the bellcrank of my current 35-powered stunter. Anybody see a problem??
Dubro 2-56 clevis has worked fine for over 30 years on control horn end of fast comabt jobs.
They can be purchased with bushings, or you can put them in yourself. All that means is that you put some sort of bearing surface (bushings) in the pushrod holes. This avoids a steel wire running in a steel upright and thus quickly wearing out.
Typically, for a music wire pushrod, you would probably want to use brass tubing that fits over the wire. Drill the hole in the control horn upright out until it fits aroudn the brass tube you need, then solder it in place. I usually leave the tubing full-length, solder it in, then cut the excess off. A lot easier to handle the tubing that way. Usually, the remaining piece only needs to be about 1/16" long.
Many people use large ball link rod ends instead, which provide their own bearing surface and never wear out or get sloppy.
Brett
Circlepilot
Circlepilot
yes, that is an easy way
That has not been the general experience. Steel/steel is notorious for wearing out in this condition
Brett
Well, I guess we will agree to disagree. People have been putting bushings in control horns to limit wear since at least the early 50's, so I think that I am not alone in my opinion.
And for the record, I don't think I have any engines that run steel pistons with steel liners. My engines have aluminum liners covered with chrome, and aluminum pistons. The closest I have it iron/steel, and they do indeed wear out very quickly without sufficient lube.
Brett
1/ Pin and bushing material of the same type is just wrong idea, they tend to bond each other. Even steel piston in steel cylinder is not the same material, but anyway, we know that steel piston engines are those needed very good lubing and do not last too much. Soft aluminum in hard chrome will last with worse lubing far longer.
2/ Correct bushing have to be of hard pin in soft hole. The reason is not to damage one of surfaces. Such damaging causes quick wear of that other.
3/ That soft material needs to have several properties, but most important is self-lubing. The best is sintered material soaked by lubricating fluid … that is difficult to have but composition of cupper with another soft metal is enough also.
4/ Another needed property is adaptability. The bushing must be soft enough to adapt its shape to pin and also allow to intrude foreign particles to the surface and thus not to allow damage the hard pin. Therefore it needs bushing material with low limit of elasticity to allow plastic deformation at that place.
5/ But on opposite side … you must allow point 4/ and not to allow changes of hole shape. Therefore the area must be large enough to keep pressure at pin load under the elasticity limit (Hook’s law I think) even if the limit of elasticity is needed low - you just need larger area for pressure and thus at existing pin diameter wider bushing, not only thin plate of horn.
Yes it is complex engineering, but replacing of thin hard plate of steel by wider tube of softer material is easiest you can do to give longer lifetime to such a join.
* Horn wear difference between a practicing competitor and a Sunday fun flyer are great.
* A typical stunt ship (at least the older ones) do not allow ready access to the control horns. It's only prudent to use bushings as protection against a failure you can't track - even if you don't fly enough to compete.
As another point, though, I'm always struck by the focus on the horn bushing or lack of one, but not with the horn solder joint. Even Igor's example above makes me suspicious about the solder joint - especially since it must hold in shear while under torsion. Critical joints are usually wrapped with wire to spread the load of the solder (as in split flap horns), but I've never seen anyone do that to a horn/wire joint. Silver solder is no magic panacea, either.
Tom B
flaps are another story with higher load, but it could be solved by little trick as you can see on picture below that short auxiliary piece of wire expands the join area
I certainly should've added before that your work is always something to be admired. I was only speaking about soldered control horns in general. I learned the wire-wrapped solder technique from building old slot car chassis, and silver solder was not as good as a wrapped joint.
That's a neat trick with the flap horn, though.
Tom B
Don't take it personally - it wasn't meant that way. I agreed with you on the bellcrank. It may be that many of us don't have the skills you have, and a bushing works better for us. I saw bushings recommended many times in the old days, too - even ball bearings - although I never got to see that one detailed.
Your lube is a good idea. After all, how long does it take a con rod to auger out, and after how many revolutions? Horn usage pales in comparison.
Tom B