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March 2019 Elevator Trim Cable Tension

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  • #16
    Originally posted by James View Post
    Yep ZK - that's how I would do it as well. The tensionmeter will tell me I'm in the zone, and there should be min 3 threads engagement, I'd assume, but I'll try to get my hands on a copy of AC43.

    James
    All AC's are freely available.

    http://www.faa.gov/documentLibrary/m...-1B_w-chg1.pdf

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    • #17
      Noice!
      Thanks mate, I'll do some reading :-)

      Jams
      The Barrows Bearhawk: Who knew my wife could get jealous of a plane?

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      • #18
        I have a reasonable amount of experience with cable and fittings from the sailing world. Nico-press are not that desirable, but they are more than good enough for our application. Wire nuts are the worst, and used commonly in some fields. Cables used for structural applications are much different than airplane use. 1/8" cable tensioned to 30 lbs? Talk about overkill. The only reason to use 1/8" cable is friction and wear. Our control application doesn't even come close to any limit for the cable. It is just not a factor, or worth worrying about. Our controls use 1/8" cable for wear and tear.

        Friction and wear are something to worry about.

        A go/no go gauge is more than adequate to judge the quality of an 1/8" nico press in an airplane control system. The cable is good for, off the top of my head, 1800 lbs. Over time, corrosion at the nico press is an issue, but the cables will probably be worn by then.

        Swaged terminals are far better. Good to the strength of the cable, at a minimum. They are overkill for our requirements. ACS charges I think 6 bucks a swage. I ended up with mostly swaged ends because they made larger adjustment easier, lighter, and a little cheaper than turnbuckles. I used nico press and a thimble in a few places where the fitting was making a 3D actuation. The thimble and nico press made a great universal joint. Aileron connection to the stick and flap actuator at the wing root come to mind.

        I did not use swaged terminals because they were superior for our application. Nico press is more than good enough.

        Do make good cable fittings and use a go/no go gauge. But getting into the nitty gritty is really way out there for 30 lbs of tension. I doubt the max load on any cable is more than 100-200 lbs. Wear and tear is the risk, not failure due to excess load. I paid extra for "pre-stretched" cable from ACS. I didn't do it because I was worried about stretch. That was all they had in stock, and I had already waited over a month for the cheaper stuff.

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        • #19
          Thanks for the insight on cable tension Svyolo, I'm not really familiar with the swages, and all my turnbuckles and thimbles are already in the kit, so I'll stick with them.

          But maybe on my next plane! :-)

          James
          The Barrows Bearhawk: Who knew my wife could get jealous of a plane?

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          • zkelley2
            zkelley2 commented
            Editing a comment
            I had to replace the nicopressed cables on the flap arm at the wing root with swaged cables from spruce so the nicopress didn't rub on the rear spar. It has it's uses.
            Another place, and while I don't think many people if anyone chooses this route, would be the flying wires on the tail could be tensioned cable instead of the streamlined or round stainless material. You wouldn't want a nicropress out in the wind and elements. Either way cables are a lot more drag, but they're wildly cheaper.

          • svyolo
            svyolo commented
            Editing a comment
            I was going to do the same, I bought them and started making the cables. I have nothing against nico press, and the price is right, and I had already bought them. But then I started using the turnbuckles. I couldn't believe how little adjustment they have, although that does make them lighter. I read a comment that Bob doesn't use turnbuckles, and did a little ACS searching on their website.

            MS21259's are swaged, threaded studs. They come in R and L hand threads, and they have a hole for a safety wire. I have 1 turnbuckle on the trim, and one on the elevator. The other cables have 1 MS21259 on one end with a threaded fork that gives just under an inch of adjustment.

            I didn't do it, but I think a slick way to rig the aileron cable in the cockpit would be have 1 R hand and 1 L hand stud join in the overheard with a turnbuckle. Very clean and easy to adjust aileron cable tension.

            Unfortunately I also bought a whole set of turnbuckles.

        • #20
          Right, sounds interesting - I'm a long way from ACS (and a 4 month turn-around on orders) - it looks like you need a pretty expensive (and hard to find?) tool AT520DC, plus the right dies to swage these terminals yourself. I might have to stick with the nicopress.

          When I hung my wings off and drilled the flap arms, I was lucky - the cables just clear the rear spar plate. But I'll put some teflon chafe tape there just in case the cable slaps when I release the flaps.

          I was thinking about putting a turnbuckle on the aileron cable at the location you describe, that would make it easier to remove each wing without feeding the cable right through the runs. But then I wondered whether it was worth doing this.

          Maybe ZK when it's time do replace the flight control cables, and I've learnt what works and what doesn't, I might grab one of these swaged cables. On the other hand, I'd be interested in learning more about their use for the flying wires - did you record the cable measurements you used?

          Ok, that's enough from me on the forum - it's time to plan a solo nav flight to Canberra and back this afternoon. My instructor keeps pressuring me to finally finish getting my pilot's licence, but building is more rewarding, and it gets in the way of the flying :-)

          James
          The Barrows Bearhawk: Who knew my wife could get jealous of a plane?

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          • zkelley2
            zkelley2 commented
            Editing a comment
            I did not use cables for the flying wires, I used round stainless because there's a guy up here that can make them and turnaround time was a couple days rather than the 6 months brunton's wants. I think for you there's a guy in NZ that can do streamlined or round.

            I do have a turnbuckle in the middle of the fuselage for the aileron cable. Highly recommend that.

            I put teflon tape as well on the spar, but it wasn't an issue except at full flap extension, then it rubbed.

        • #21
          Thanks, as always ZK - priceless information from a guy who's been there, and done what I'm trying to do.
          You can't beat the wisdom on offer on this forum.

          Survived the nav to Canberra, so back to building tomorrow :-)

          James
          The Barrows Bearhawk: Who knew my wife could get jealous of a plane?

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