Extra wing rib braces?

[Johnny]

Hello fellow aviation enthusiasts,
I have thoroughly enjoyed reading many of the helpful solutions and encouragements.
I have purchased a KF4-1050 last year. The wings and airframe were already covered and painted, no engine. The wings have 13 gallon tanks. Upon closer inspection of the wings, noticed extra braces installed on the fwd part, inbd/otbd sides of all the wing ribs and attached to the fwd spar with 1/8x3/8 rivets. Each support bracket on the fwd spar has been attached with two rivets.All these extra supports are not depicted on the wing assembly instructions.
1. I'd like to know if this has been accomplished on any KF4 for starters.
2. If I conform my wings to the drawing as depicted, would there be any problem using universal cherry max rivets to plug all 1/8 holes on the fwd spar?
3.Should the fwd spars be replaced or leave the additional braces?
All the green lines drawn on the diagram, represent the extra braces installed. The other diag shows dimensions of the braces which was to be installed only on the #10 wing rib.

Looking fwd to all your insight,
JC

[jiott]

Wow! I see no point in those extra braces. All they do is stabilize the ribs, which in my opinion needs no more stabilization due to the main spar cross braces that pass thru and are glued to the ribs near the point where all those extra braces are. The ribs are not really much of a structural part of the wing; all they do is serve to hold the fabric in the proper airfoil shape and hold the trailing edge. The structural part of the wing is the spars and the cross brace/drag tubes. Seems to me that those extra braces are just added weight.

[HighWing]

My thinking is that since the holes were drilled for the extra bracing on the lateral side of the spar - similar to the shear web on a rib, it likely doesn't weaken the spar significantly. That being said, however, I would't feel comfortable if my name was on the Airworthiness Certificate as the "Manufacturer" and therefore legally responsible for the final design and assembly. Thinking down the future, my main concern would be for you to consider how comfortable you would be selling it as a flying airplane as it is currently assembled when and if that time comes.

[Johnny]

There's about a 10inch gap between each brace attached to the spar as seen from the wing tip. I'll be opening the wing this weekend for a structures technician to give me his final say.
Thank you so much for your valued opinion.

[avidflyer]

I typed this a few days ago, and then didn't hit the submit reply button, but maybe will now. There have been thousands of these wings built and flown at various weights between Avid Flyers and Kitfoxes, not to mention the other designs that also are copies of them in one form or another.
In fact clear up to 1500 lbs. or more.
That's about1/3 more weight then your 1050 gross weight. I don't believe there were any wings falling apart in the sky. Why do people think they need to improve on an already proven design. JImChuk

[Johnny]

I don't understand why people think they need to add to a proven design. It was pretty disappointing realizing all these braces were not on the manufacturer drawing.
Thanks for ur post.....

[Guy Buchanan]

1. Not here.
2. Your question is a little confusing, but the only problem with filling holes would be if the rivets were stainless and caused corrosion. Alu rivets would be fine, but in my opinion unnecessary for two 1/8" holes in a 3" tube along its shear center.
3. The wings are covered satisfactorily? I'd leave them. The weight's not worth the hassle and otherwise I can't see a detriment.

[avidflyer]

Guy, did you mean steel rivets causing corrosion? I don't think SS rivets cause corrosion to aluminum. That is what Kitfox supplies for riveting all the pieces to the spars. (I didn't want Johnny worrying about corrosion as well) JImChuk

[Guy Buchanan]

Well, any time you put stainless and aluminum together you get electrolytic corrosion, particularly if you're in a humid or marine environment.

More than you ever wanted to know. (http://www.worldstainless.org/Files/issf/non-image-files/PDF/Euro_Inox/Contact_with_Other_EN.pdf)

[Johnny]

The wing coverings are fantastic. I get the dissimilar metal issues. Already added additional inspection holes for my structural technician to inspect the spar. After the braces are removed from the wing ribs, those areas will be inspected and reinforced per the AC43.13-1B.
My thoughts for removing the braces.
1. Not on the original drawing
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.

[t j]

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.

[jiott]

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).

[TJay]

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,

[avidflyer]

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

[neville]

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.

[efwd]

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

[jrevens]

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.

[efwd]

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

[David47]

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.