Is there some "rule of thumb" for the raw length of a control cable?  I am assuming that my turnbuckles should be minimally threaded, and cable "hand tightened" - so that ultimate turnbuckle adjustment will get me into spec with turnbuckles properly threaded... but, if I could benefit from anyone's previous experience, that would be GREAT.

Thanks in advance,

Brian M

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Brian, 

Check in the Zenith construction standards. Seems like I remember some suggestions there of how many threads to have exposed outside of the turnbuckle when the cable is tight to specs and it is not very many. I did not go back and look, but it seems like the usual no more than 3 threads showing.

I played with some cable, the thimble, the clevis and the nicopress fitting and figured a mathematical way to determine the length of cable in the system and where to place the nicopress fitting so the bolt hole of the clevis would match the bolt hole on the control.

I would  pull the cable tight, mark the middle of the controls bolt hole on the cable with the controls and flight surfaces clamped in their central position, measure back some mm length I had determined by experiment and make a second mark from the first mark.Then crimp everything together from that second mark by keeping  one side of the nicopress fitting on that mark. You need to determine what the length of cable in your end and which side of the nicopress fitting you want to use.

I then could consistently create ends that matched the needs for the exact length.

I suggest you play with a couple fittings by creating a few under controlled length situation take them back apart and figure out what length of cable works for you to hit the correct means to put the clevis bolt hole on the control bolt hole.

Not an exacting answer, but how I went about it and had good luck once I got rolling.                            Jerry

Brian,

I used the same logic. Minimal threads, then tightened cables as much as possible and crimped. They would not screw in enough and I had to start over. If you get them fairly tight before crimping, they tighten to spec pretty quick.

Jeff

Thanks.  I'm also concerned about *future* tightening, as Zenith states in the standards doc that they will need to be tightened with time and use... I don't want to have the turnbuckle barrels bottoming out in 2 years.  Since it is allowable to have 3 threads showing, maybe I'll try your method starting with 4 - 5 threads out.  I'm assuming that it will take at least a thread or two of tightening the turnbuckle before hitting the tension spec.

Brian M 

Hi Brian, how did your cables turn out? Im ready to crimp my nico sleaves onto the turnbuckles at the rudder horns. If I understand it correct, I need to pull the cable tight  and have the turbuckle screwed all the way out and then press the nico sleeve? This step makes me nervous!  If I mess it up, I have to remake the whole cable, lol

Steven - Jeff Cochran was right. We ended up crimping with about 5-6 threads showing on the barrel, cable pulled "just barely hand tight". When you tighten the turnbuckle it will come up to 30 lbs real quick. I ended up with just 2-3 threads showing, right at proper tension.

Brian
P.S. - I purposely over-tightened by about 10-15 lbs. and let it sit for a week and then re-tensioned. They lost about 5 lbs. just from sitting for a week. It's normal for the cables to "settle in" a little bit.

What did you use to crimp to nico sleeve?  I have seen some using what appears to be a bolt cutter type crimper that puts 3 crimps on the sleeve as shown in the construction manual and I have also seen some that used a manual bolt tightening crimper that only puts one crimp on the sleeve.   Is there any difference in putting one vs three crimps? 

I'm curious about this too. The EAA video on the subject shows them putting in two crimps, the second one being used to iron out the ridge that the first one put in.

http://www.eaavideo.org/video.aspx?v=2079771339001

That video is showing 3/32 cable.  1/8 cable uses a single sleeve with 3 crimps.  

I bought the "cheaper version" sleeve compression tool from ATS.  It's basically the same (operationally) as NicoPress tool - maybe not as durable and may require some minor adjustment, but for my needs quite adequate and MUCH simpler than the manual vise tool.  It crimps an area about 1/4" wide, and you should be making THREE crimps per sleeve.  The first crimp is in the middle, the second crimp is on the thimble side, and the third crimp is on the "tail" side.  The sleeve should look like it has 2 "raised" bands in-between the crimps.  My tool did a great job and the sleeves all look and feel rock solid.

EAA Video

Brian

Thanks Brian, that helps to ease my concerns.

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