What size brass tubing for Bellcrank?

[Paul Taylor]

What size brass tubing do you use for running the lead out wire thru on bell cranks on a 40 size plane?

Bushing the leadout wire in the bellcrank.

[Leester]

1/16"

[john e. holliday]

Yep, 1/16 inch tubing.   But, I run my tubing thru a torch first to red hot before cutting to length.  Makes for easier bending.   Also sand surface with worn out sandpaper.

[Paul Taylor]

   Also sand surface with worn out sandpaper.

Hey Doc, Can you explain this a little more.?

[john e. holliday]

Well about what part?  I guess I will start with the tubing.  Run it thru a torch to red hot and let air cool.  The sand paper is to get rid of the oxidation that happens.   Cut tubing to length you want, I use 1 inch.  Check to make sure the bell crank holes are big enough for tubing to go thru.  Slide your Leadout cable(or flying lines) thru the tube.  Make sure you have enough slid thru for the wrapping that will come.   Insert both thru the bellcrank hole and bend it to a teardrop shape.  Once in place you do your normal wrap.  If doing crimp make sure furrel is on before putting the tube/line thru the hole. 

Making lines or leadouts at wing tip.   Use 1/8 inch scrap wire or small phillips to bend the tubing around after line is in place.  Seems the tubing holds the lines/leadouts while wrapping.  It is slightly adjustable before doing the wrap.  I have had the line move before doing the bend.  It is so much easier to show than write about.  There was a pictoral I made on here some time ago. But, I am tired this AM from driving.  But, then I may do a search later.   

[Bill Little]

HI Doc,

I have used 1/16th tubing to finish off the lead outs at the wing tip (instead of thimbles/eyelets) just like at the bellcrank.  Do you ever do that? 

Big Bear

[john e. holliday]

All the time.  I also don't wrap lines/leadouts anymore.  The swaging is so much easier and faster.   

[Ed Prohaska]

I have "torch phobia" and don't own a torch, but anything that makes the tubing easier to bend is good.

I use the smallest dia. tube the leadout cable will comfortably pass through. It's usually 1/16 OD, but I have used the next larger size for .036" cables. I assume the tubing I use is brass. It has the right combination of hardness and bend-ability. Hardness is important if the bellcrank is thin aluminum (Fox, Veco, Perfect or from an ARF). If the bellcrank is nylon, softer tubing could probably be used, but I've developed a feel for working with brass, so that's all I've used up to now.

By the way, I have an ARF Flite Streak and ARF Nobler with nylon cranks, NO bushing on the leadout cables and 100s of flights on them. I can inspect the crank & cable in these models and both are holding up very well. Brodak bellcranks are now made from an improved nylon that should be even more resistant to abrasion. That said, if I were building a model I wanted to outlive me, I'd probably just go ahead and bush the cables.

The photos are from an ARF Nobler and Tutor II. I bushed the Tutor's cables for another club member. Unfortunately the model did not last long enough for a second flight, so cable/bellcrank wear was never an issue. I use approx. 2.5" of tubing and 6" of cable to make the loop, then cut off excess cable about halfway through the 2nd wrap (the wrap you make after you bend the cable back over the first wrap).

I make the loops large enough so they don't jam on the bellcrank over it's range of travel, but not so large they interfere with the pushrod or some internal structure. I make the bend with a special pair of needle nose pliers. A radius has been filed into the pliers to give a smooth bend without cutting into or cracking the tube (or wire if I'm bending a pushrod). The finished loop is polished with 600 grit paper to remove scratches. I use a magnifier to inspect for cracks during the process. The thicker the bellcrank, the larger the loops need to be. Of course the cable hole in the bellcrank must be enlarged to accommodate the tube. It all adds time and effort and may not be needed with a modern nylon bellcrank, especially for ".40 size" or smaller models. EWP

[ChrisSarnowski]

Great pictures, Ed, very helpful!! I have a metal bellcrank issue on an old ship that I am fixing up.

-Chris

[Bill Little]

Pretty work, and nice pictures, Ed!

I haven't had an issue with the nylon bellcranks and solid lead outs, but have had stranded lead outs break from a metal bellcrank when it wasn't "bushed". 

Before I learned about the tubing over the lead outs, we used to flare short pieces of brass tubing in the holes of metal bellcranks for the lead outs and the push rods.

Big Bear