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Thread: Wiring in a wood wing

  1. #1

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    Wiring in a wood wing

    How should you properly run the wire through a wood wing? I imagine a small hole in each wing rib with the wire just passing through, but I wonder if there should be some sort of conduit through each rib or even end to end. I have searched and searched and can't find anything related to this.

    Thanks in advance.

  2. #2
    steveinindy's Avatar
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    Grommets to prevent damage to the wires would probably be a good idea.
    Unfortunately in science what you believe is irrelevant.

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    Quote Originally Posted by AlanC View Post
    I have searched and searched and can't find anything related to this.
    AC 43.13 1B has the standard aviation practices for wire routing.

    My personal preference for your app is non-metallic flexible conduit unless EMI protection is needed and if that's the case, flexible metallic conduit would be my choice. Conduit ID should be at least 25% larger than the OD of the wire or bundle, supported every 24"
    Last edited by martymayes; 03-12-2012 at 07:39 AM.

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    I'd run a co-axial wire and use the outer shield as the common ground, mounted in rubber grommets, or Adell clamps.

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    steveinindy's Avatar
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    Oh and you might want to be careful choosing your wire coating materials. Some of them are more prone to cracking than others which could be rather catastrophic in an aircraft that's made from wood. Tom's suggestion is a good one.
    Unfortunately in science what you believe is irrelevant.

    "I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.



  6. #6
    steveinindy's Avatar
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    AC 43.13 1B has the standard aviation practices for wire routing.
    Great resource.....here are the ones that are especially pertinent to the question at hand, since the entire document is quite long and has a dozen or so chapters.
    Wood structures- http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/list/AC%2043.13-1B/$FILE/Chapter%2001.pdf
    Electrical- http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/list/AC%2043.13-1B/$FILE/Chapter%2011.pdf
    Unfortunately in science what you believe is irrelevant.

    "I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.



  7. #7
    Hiperbiper's Avatar
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    Quote Originally Posted by AlanC View Post
    How should you properly run the wire through a wood wing? I imagine a small hole in each wing rib with the wire just passing through, but I wonder if there should be some sort of conduit through each rib or even end to end. I have searched and searched and can't find anything related to this.

    Thanks in advance.
    Just because someone someday might need to repair/replace/add-to the wires running from the fuse to the tip please run a conduit thru the ribs (or fuselage) during the bulid...
    Though you may never have occasion to use it, this feature will prevent future owners from calling you heritage into question...

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  8. #8

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    I will ask the question of whether the wood wing is plywood covered or fabric covered. There are few wires needed in a wing and modern aircraft spec wiring lasts a really long time. If the wing is fabric covered I suggest that any sort of conduit is excess weight. You will be opening the wing periodically to replace the fabric and deteriorated wiring can be replaced at that time. As I think about it, a plywood covered wing can be treated like an aluminum wing and we do not put conduits in those. Typically there are enough inspection holes to allow wiring replacement as needed.

    With some forethought, you can install all of the wires that you will need when you originally build the wing. You need wiring for a ground, a position light, an anti-collision light, and maybe a landing light. Put an extra in for good measure and skip a conduit. You are not likely building a 747.

    Make a wiring diagram for your ship and note the wire sizes. Also use wire tags to number the wires and put those numbers on your wiring diagram.

    Best of luck,

    Wes
    N78PS

  9. #9

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    Thanks to everyone for their insightful replies. It has really helped inform my planning.

    steveinindy + tom downing - the coaxial wire through nylon grommets or adel clamps seem like a pretty good way to do it.

    martymayes - thanks for the conduit suggestion and the AC43 reference (though everybodies suggestions are ok by AC43)- I didn't realize there was a plastic flexible aviation electrical conduit - it's not carried by my normal suppliers. It seems pretty light - so if I can afford it I'll go with it!

    hiperbiper - your admonition carried the day for the conduit - I've always left a string to pull another wire in every computer room I've wired, so why not here?

    wliu - it is a plywood covered wing with fairly limited inspection holes - so there is no chance of fixing a broken wire unless there is conduit. Your right about the wires though, only a few will ever be needed.

  10. #10

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    If I may offer a couple of suggestions, history suggests that a plywood covered wing needs as many inspection openings as an aluminum wing. If you look at the AD's for wood wing or just wood spar airplanes, you will see that thorough annual inspection will let you catch small issues before they become large ones.

    My other insight is that weight is the enemy of performance and if you look at how light aircraft are designed, you will see huge trade offs made to reduce weight. The point being that ounces count when you only have 100 or 200 hp to pull you aloft. There is a famous story about how Leo Loudenslager swapped airplanes with another will known airshow performer who flew an airplane that looked just like Leo's Laser. The other pilot was shocked to discover that Leo's airplane stalled 10kts slower than his and had the corresponding better performance when pulling around corners and doing other things that acro pilots look for. Looking around the airplane the difference was that every extra ounce had been removed. Every bolt had been trimmed in length so that exactly two threads showed Lots of seeming minor details had been attacked so that every part was the minimum weight to do its job and no more.

    So the point of the paragraph above is that you can put a conduit in, but Cessna, Piper, Mooney, and all of the teams that build light aircraft have made the conscious, intentional, choice to not add that weight.

    Best of luck,

    Wes
    N78PS

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