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Thread: Cable Tension: do the cables ever stabilize tension wise

  1. #1
    aeroaddict's Avatar
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    Cable Tension: do the cables ever stabilize tension wise

    Plane; EX-2, 1/8" dia cables. 234hrs on the hobbs.

    Doing my second annual and both the aileron and elevator cable tension are low again. The first annual I thought, ok, new cables will stretch but eventually settle in.

    Question: do the cables eventually stop streching?

    The ailerons are easy to retension, but the elevator cable turnbuckles are almost impossible to access, I mean it's a royal PITB!
    Last edited by aeroaddict; 10-06-2021 at 02:22 PM.

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    wireweinie's Avatar
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    Cable tension is directly related to ambient temperatures. Lots of tension gauges have a 'cheat sheet' with them that corrects for ambient temps over or under the 'standard' of 59ºF.

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    behindpropellers's Avatar
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    You may want to dig deeper and see if you have other problems.
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    aeroaddict's Avatar
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    I'll look for a temperature co-efficient chart in the box.

    Other problems such as???????

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    Quote Originally Posted by aeroaddict View Post
    I'll look for a temperature co-efficient chart in the box.

    Other problems such as???????
    cable routing, pullies wearing funny etc.
    get a mirror and flash light and give everything a good looking over.
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    Quote Originally Posted by aeroaddict View Post
    I'll look for a temperature co-efficient chart in the box.

    How will that help?

    Sure the cable length depends on temperature but how tension depends on temperature depends on the expansion of the cable and the expansion of the airframe that supports all the pulleys and cable attachments. Given that aluminum spars and ribs have a higher coefficient of expansion than the steel cables wouldn't you expect the aileron cable tension to increase as the aircraft got hotter. Steel elevator cables in a steel tube fuselage would probably have tension essentially independent of temperature.

    Well that's my theory. Someone with years of experience measuring cable tensions may shoot me down.
    Last edited by frequent_flyer; 10-06-2021 at 10:12 PM.

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    aeroaddict's Avatar
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    Thanks for the responses. Yes I'm aware of wore parts, fraying, ...... can effect the tension.

    BUT, my question was; do the cables continue to relax or do they eventually come to a 'permant point' and do not stretch/relax further (whatever you want to call it).

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    I’ve never had to re adjust cables as a result of cables “stretching” cables don’t stretch. They may “wear in”, seat into pulleys, relax a bit as airframe/wings settle in - OR cut thru a lacing cord they were inadvertently routed around - Give everything a good looking over. Then overcome the aversion to tightening elevator turnbuckles and snug them up.

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    wireweinie's Avatar
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    Here are temperature notes from Cessna, DeHavilland, and a tensiometer manufacturer.

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    Steve Pierce's Avatar
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    Aircraft cable should be pre-stretched. I have not noticed a change in cable tension on the Cub Crafters products but I have not been specifically checking either. I have found frayed cables at the top aileron cable pulley on top of the wing as it goes over the spar. Theory is they had some bad cable. My opinion, they tighten those aileron cables awfully tight. Have also found the bolts at the bottom of the stick tight so that they are not swiveling which would have an effect on tension. You are right, the turnbuckles at the elevator are a PITA. I know someone who installed them under the back seat in the Super Cub.
    Steve Pierce

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    aeroaddict's Avatar
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    Thanks all. I probably should have mentioned my cables are maybe 10% less, it's not like their flapping in the wind.

    My question was more of a long term type as I continually learn to be a better mechanic.

    PS; GREAT idea on the elevator turnbuckles under the seat. Maybe next plane.

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    Quote Originally Posted by Steve Pierce View Post
    My opinion, they tighten those aileron cables awfully tight.
    CubCrafters FX-3 AMM specifies 45+/-5 lb with no temperature defined. What is specified aileron cable tension for a PA-18?

  13. #13
    aeroaddict's Avatar
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    I'll let the 'real' cub guys speak, but CC's apprear to have the same tension spec's as the pipers; 45+/- for the aileron, 60 +/- for the elevator.

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    BC12D-4-85's Avatar
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    I recall in well below zero cold my aileron cables wrapping around the lower end of the lift strut. They can get loose enough to do that. Doesn't take much of a hard turn to make one side to go slack or they get bumped over while loading. Then there's that strange metal sawing sound until corrected.

    Gary

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    Steve Pierce's Avatar
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    I have seen aileron tension said to be 30 ft/lbs on the PA18 but don't recall an official tension. I like about half of that.
    Steve Pierce

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    Here is one specification for PA-18 cable tensions - https://www.univair.com/content/Pipe...e-Tensions.pdf

    I found some discussions on this site with opinions ranging from "must be exactly to spec" to "whatever feels right".

    Years ago I had a share in an Aeronca 11BC Chief. The first IA to inspect it insisted the aileron cables were too slack and tightened them to "spec". The aircraft was almost unflyable and we put them back to the previous tension.

    Now I'm wondering how important it would be to keep my FX-3 cables at the tensions specified by CubCrafters. I only have to satisfy myself as I do the maintenance and the inspections. I'm tempted to simply record them and watch for any trend.
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