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Thread: Extra wing rib braces?

  1. #11
    Senior Member t j's Avatar
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    Default Re: Extra wing rib braces?

    2. Possibility of a future problem due to vibration where the added braces attached to the wing spars.
    Over kill? Probability, but I'm thankful for this forum and all your replies.

    I agree. Also, the wings need to be able to flex in flight.
    Tom Jones
    Classic 4 builder

  2. #12
    Senior Member jiott's Avatar
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    Default Re: Extra wing rib braces?

    The galvanic corrosion issue between SS and aluminum is very interesting. Obviously there is scientific information that shows this "could" be a problem. However, from a practical real world standpoint it must be a nearly negligible amount; at least in the Kitfox wing spar environment. Kitfox has been supplying SS rivets for the very critical spar to lift strut and cross brace brackets for many years now. I have not heard of any corrosion problems in this area, even from guys who fly floats on a regular basis. If someone knows differently, I would be interested to know. That being said, if I were just using rivets to plug some holes in the aluminum spar, I would go ahead and use aluminum rivets. I like the idea of plugging the holes with rivets because they put the ID edge of the hole in compression, which should help some in preventing a crack from starting at this stress riser (probably a moot point since the stresses are very low at these holes in the center, neutral axis, of the shear web).
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  3. #13
    Senior Member TJay's Avatar
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    Default Re: Extra wing rib braces?

    Its not just Kitfox, look at Sonex there's over 12000 SS rivets in an aluminum Airplane, To me taking those braces out is foolish, Leave them in, In my opinion it is not much different than gluing composite or aluminum leading edge across the wing,

  4. #14
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    Default Re: Extra wing rib braces?

    TJay, I wish this site had a 'like' button. I would press it for your post. I agree completely with what you said. (Not positive about the number of SS rivets in a Sonex, but I know you built one so I'll take your word for it on that) :-) JImChuk

  5. #15

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    Default Re: Extra wing rib braces?

    A little note about AL and stainless: having worked in aviation and marine electronics for 40 years I dealt with the issue with radar wave guides, AL rectangular guides connected with SS hardware. In the marine environment the addition of saltwater created bad corrosion at the joints. The Radar manufacture provided a paste called densachrome which was applied to the hardware to stop corrosion. The corrosion level in aircraft electronics was minimal unless working on float planes.

  6. #16
    Senior Member efwd's Avatar
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    Default Re: Extra wing rib braces?

    While were on dissimilar metal issues. Take an airframe, remove the powder coat and then attach an aluminum terminal end to act as a ground. How long before the ground is no good? Brass ground Bus attached to the airframe with Aluminum terminal ends. Im asking because I just made that connection on my ELT antenna ground.
    Eddie

  7. #17
    Senior Member jrevens's Avatar
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    Default Re: Extra wing rib braces?

    Quote Originally Posted by efwd View Post
    While were on dissimilar metal issues. Take an airframe, remove the powder coat and then attach an aluminum terminal end to act as a ground. How long before the ground is no good? Brass ground Bus attached to the airframe with Aluminum terminal ends. Im asking because I just made that connection on my ELT antenna ground.
    Eddie
    It's highly unlikely that the terminal ends are aluminum, Eddie. They are most likely tin-plated copper. One other point - with electrical connections (or any connection for that matter) between dissimilar metals, one of the most important factors for maintaining a good, corrosion-free connection is to make the mating surfaces air (& moisture) tight. That's what you have with a properly crimped terminal to wire connection. One of the things that I do with many of my screwed or bolted together connections is seal them with a little bit of silicone laquer that is meant to be used for spraying on completed printed circuit boards to protect them. I spray a little in a dixie cup & use a small disposable brush to apply it - it wicks around & into every crevasse to make a nice airtight seal. I just happen to have some of that, but probably any fast drying sealant would do the job... maybe clear nail polish? A clean, tight connection to begin with, and then seal it - maybe overkill, but an effective little bit of "insurance".

    Stainless steel & monel rivets have been used successfully on aluminum aircraft structure for at least as long as they have been available as pulled or "pop" rivets. The densachrome comment by neville was interesting. One of the things that many of us would do when using that type of rivet on our aircraft is use zinc chromate primer, not only between faying (or "touching") surfaces of dissimilar metals, but aluminum to aluminum also. I was taught in that regard that a thick coat was not needed, or even desirable. Supposedly only one layer of molecules would do the trick. I was told it was the chromate ion that protected the aluminum (perhaps having a sacrificial effect?). One thing we would do is dip each rivet in thin zinc chromate primer before inserting & pulling it. This not only seals & protects that joint between dissimilar metals, but it also made the rivets a little easier to remove if you had to drill one out... it would act like a glue & help prevent a rivet from spinning in the hole, which is a potential problem with s.s. especially. A further comment in regard to the Kitfox & s.s. rivets on the spar - those rivets are probably very well sealed, not only with the epoxy that is used, but also in some instances by primer that is applied. I would not worry about those rivets for a second as far as dissimilar metals are concerned.

    The rivets on the Thorp T-18 that I built are 99% solid aluminum, but there are a few s.s. & monel ones, and in the 26 years that I've flown that aircraft I've not had a single problem or sign of corrosion with any of them - not one. The same is true of every electrical connection in the airplane. FWIW.
    Last edited by jrevens; 02-16-2017 at 09:38 AM.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
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  8. #18
    Senior Member efwd's Avatar
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    Default Re: Extra wing rib braces?

    Your absolutely right John. Forgot what they were made of. Thanks for the information. Very helpful tips. Thanks
    Eddie

  9. #19
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    Default Re: Extra wing rib braces?

    Just to back up John's comments, if you exclude water or other electrolyte forming fluids from entering the joint, whether it be an electrical bonding joint or even ss rivets into Al then you prevent corrosion. Sealing electrical bond joints with a good sealant and dipping rivets into a primer at installation is good general practice for any riveted or bolted installation. If you look at the galvanic corrosion table that lists materials according to their potential for galvanic corrosion interaction, even al alloys with different alloying elements (e.g. 2000 series or say 7000 series) can have the ability to set up an electrical potential difference. Having said that though, I've never seen corrosion between dissimilar al alloys in my 40+ years in the industry, the exception, however, being 5000 series al alloys which contain magnesium. So in general, my thoughts would be if there's the potential for water ingress into the joint, then Mr metal cancer will look for any excuse to do his worst. Suggestion: wet assemble mechanically fastened joints where ever possible.
    Last edited by David47; 02-22-2017 at 04:30 AM.
    David
    SS7 Builder

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