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Building Tips and technical articles. => Building techniques => Topic started by: Russell Bear on August 30, 2017, 05:29:01 PM
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Building the Brodak profile Oriental and have a question on the lead out wires on the bellcrank. The plans are not specific on the mounting and crimping / wrapping on the lead out wiresnkn the bellcrank. Is it necessary to run the cable through a spall piece of tubing that is bent on the bellcrank for a relief? I assume it's ok to just install the able alone and either crimp or wrap?
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Use the tubing through the bell crank holes. I run brass tubing through a torch to red hot and cot to length. Run cable through the tubing before inserting into bell crank and bending it. Then finish the wrapping of the lead out. D>K
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Russell, if you don't have a torch to heat the tubing the wire through the bellcrank will work. Doc is right in using tubing but it will take along time to wear through the hole in the crank. I don't like crimping on the heavy lead out wire, if you can wrap with copper wire. It is best to double wrap then notch the first rib so there is no binding. Do all your wrapping before installation, it is much easier.
Rich
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I suppose it depends on how much risk you want to take. And, how long you want to fly that plane until you get something else.
As far as simply passing the leadout wire thru the bellcrank, using no brass tubing as a sleeve, it can work. The question is, how long? I have seen some fail rather early, and others last far longer than I thought they would.
It will take time for the unsleeved wire to elongate the hole in the bellcrank. But, I also wonder about breaking wire strands. Another issue is flex. That wire loop will flatten under load, then spring back when load is removed. This repeated flexing can lead to a fatigue failure. It may take a while for that to happen but you never know how long.
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I've found the Brodak bellcranks very resistant to wear using .027 stainless. Just make a smooth loop around around an eigth inch rod and fit it in place. Unless the ribs force the leadouts into weird angles the wire will smooth off the inside edges of the hole in a few flights.
"monoline" buttons work forever. Just a simple turning with about a .280 large diameter necked down to 0.1 in x .05in. and then down again to .075 long enough to extend 1/32 past the bellcrank. It gets peened in place with a hammer that locks it in place very firmly. The same kind of leadout loop just pops over it. This a perfect job for those little 7x10-14 lathes.
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I like the horseshoes made with 1/16" brass tubing. Bernz-O-Matic torches are cheap and they have a lot of uses for the modeler.
Cut the tubing to 1" lengths before annealing. An additional benefit is that when you bend the tubing & wire cable together they become locked together and the crimping or wire wrapping is just extra insurance.
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Easier to cut after annealing the tubing and I go 1 1/2 inches or more.
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Thanks for the responses everyone. The 1/16" tubing worked great after annealing and the crimps look great. Thanks again...
Sent from my iPhone using Tapatalk
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The old fashioned rule of thumb was if using cables, use a plastic bell crank, or use solid wire in a plastic bell crank. If using a metal bell crank, it would cut the cable pretty quickly, as was seen on early ARF Noblers, and they need to be bushed with a brass bushing, or, again, use solid wire for lead outs. These days, I am like the others here and use the small tubing, brass or copper, as it covers all the bases. With tubing that small, a simple candle will get hot enough to heat it to a red color for annealing.. or a gas stove burner.
Type at you later,
Dan McEntee