wing rib gussets

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gicummo

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Nov 19, 2009
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montevideo / uruguay
Hello everybody;

I have a problem, I'm traying to resolve it by two or threee differents ways, but I want to know from you why I could be wrong or wright.
I can not find 1/16 plywood for the gussets where I live, minnimun 3mm and it isn't very good; so I build my own 1/16 gussets in three ways:
1. three layers of wood sheets (think enough)
2. three layers of fiberglass (the middle one at 45 degrees). the fiberglass is of 200 grs/m2
3. two layers of wood and the center with fiberglass (at 45).

I need to make gussets for 28 ribs (pietenpol),

the case 1, is the most "rigid" and heavier (I glued with epoxy), and the most difficult to build because I have to cut a lot of sheets to make the center layer, keep it in place without move, etc.. it isn very difficult, but it isnt easy too.
The case 3 is the easyest to make, but is too flexiblein any axes. it is very strong in tension, even compresion, but it bend more than 1.

But I want to know If I could replace the plywood gussets with fiberglass gussets, and why. I think I am going to build them of wood, but I have my doubts why not fiberglass

thank you

mario
 

Hot Wings

Grumpy Cynic
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If it were me I'd grab a pair of scissors and some thick water color paper. Paper gusets were good enough to last 70 years in my Aeronca I suspect they are good enough for a Piet.

The original Aeronca paper was called "fish" paper and is used for insulation in electric motors. Some gasket paper at the auto store appears to be the same material. Semi scientific testing indicates the water color paper soaked in glue, which is available just about anywhere, is an acceptable substitute.

You have to step back and see what the gussets do for the structure. Make up a sample test intersection with the same materials you plan to use, let the glue set, and then try to break it. If the stick for the rib breaks first the gusset is doing it's job.
 

rheuschele

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My first question is: Where do you live that you can't find this?
Second question: Is it worth your life or the life of the people flying with you?
Honest to goodness finding this shouldn't' be a huge problem, your on this discussion group. If your in the US, then it's an easy answer. If your in a different country, then your choices are to ask someone on this board to get it and ship it to you. It may, and probably will come cut up and in a smaller box for shipping reasons.
As for the water color paper, there is a good point here, but I might be inclined to use something along the lines of soda pop cardboard cases. There is a discussion group on Yahoo called "chuggers", that deal with the use of everyday materials for single seat, inexpensive aircraft.
Ron
 

gicummo

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Incredible ¿no?, but theres only onle place where to buy 1/16 ply (a hobby shop) and today do not have and don't know when they will.
Paper better than fiberglass?.. great, I am goint to test them too.
Uruguay is where I live.

mario
 

Hot Wings

Grumpy Cynic
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Paper better than fiberglass?.. great, I am goint to test them too.
Uruguay is where I live.

mario
Paper better than fiberglass? Strength to weight, then no. Adequate strength, availability, and compatibility with wood glues? - then yes.

The key to using alternate materials is to test. The soda pop carton paper, 90 pound Kraft paper, or even red rosin roofing paper might work too.

I suggest the water color paper only because I have tested it compared to the Aeronca material.
 

Dauntless

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Mario,

I have a composites business, and work with 200 gsm fiberglass and carbon fiber every day. That cloth will be about .008"-.010" per layer when cured with resin under vacuum. To get 1/16" thick (0.0625" or 1.6mm) you will need at least 6 layers, maybe 7 or 8, depending on the weave and how much vacuum you can get.

The good thing is that it is easy to make exactly what thickness you need. It is very strong, and will last longer than the life of the airframe. Calculate how many square centimeters you need, cut the cloth (alternate layers at 45 degrees), wet out with resin, and cure under vacuum. Then draw out the pattern for the gussets directly on the cured glass with a pencil and cut out with your favorite saw. Epoxy to the ribs per the plans and you are done!
 

gicummo

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Dauntless, skeeter_ca:
thank you, i feel more relax now; fiberglass with epoxy is the easyest solution I thougth, but I do not see any note about this theme except this one (Ultralivianos & Experimentales: “Pañuelitos” de fibra de vidrio y epoxi.), and I was not very shure about it. As you, he said to use 2 pieces of 3 layers each one, of course is easyest build one with 6 layers.

Just one thing, why vacum? I have a little vacum machine from a medical machine that was brake (the big machine, not the vacum one), May be it is enogh,,,

Mario
 

Topaz

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Be sure to either peel-ply or sand the surface that will be bonded to the wood. Epoxy cures with a shiny finish, and that can be tough to reliably bond to something else.
 

skeeter_ca

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You are using an epoxy for the wood rib parts right? Most likely T-88. MAke sure it's compatiable with the resin for the fiberglass.

As for making the gussets, you don't have to vacuum bag them, but it would make for lighter gussets. Don't be so concerned about making them 1/16" thick. I would think that 1 ply of maybe 1-4oz bidirectional cloth would suffice. If paper gussets have been used i would think the fiberglass ones would be about 100 times stronger. Maybe wetout the cloth on a glass sheet and when dried pop it off and cut it up.
 

Dauntless

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Mario, I read the website (yo vivi en Guatemala cuando era un chico...entonces hablo espanol). It has very good instruction, but I would still make the gussets with enough layers to be 1/16" thick. Thick is strong!

Vacuum makes stronger gussets. If you don't use vacuum you can have too much resin in the laminate, and the gusset will be weaker than if you use vacuum. A small medical vacuum pump will work fine for this small piece.

As Topaz suggests, be sure to use peel ply, or sand with course grit paper to make a rough surface to bond to the ribs.

To ensure resin compatibility, use the same resin for the laminate as you use to bond the wood. T-88..right?
 

Topaz

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Couldn't you just have the right plywood shipped? I mean, get Aircraft Spruce to cut some down to smaller sheets to keep the costs (and likelihood of damage) down, and FedEX, baby! How expensive could it really be, versus all the extra labor of doing 'em in fiberglass?
 

Topaz

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True. I just don't like seeing substitutions. Build it the way the designer intended, IMHO. And a Piet with glass gussets? Heresy! :)
 

shafferpilot

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a quick caution and i'll go. "strength" of any material is a very subjective concept. Hard thick stiff fiberglass is certainly much harder and stiffer than the original gussets... That's actually not a good thing in a mostly wooden structure.

Structures need to flex. Made all in wood, the wing flexes and all the individual components share in the flexing and loading. Replace some of those components with stiff ones and the wing looses a lot of strength since the stiff components concentrate the stress on the flexible parts and brake them when the overall load is much lower. Having said that, I don't think the gussets are a particularly risky place for this type of problem since they don't do much flexing anyways.

My point is to say that matching "strength" of the original part is the goal, not making it 100 times "stronger"
 

HumanPoweredDesigner

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When making composits, I would think it is important to make sure the stronger material takes all the compression stress, and the weaker one is only used for webbing. If you try to make both take the stress, the different young's moduli will cause only one of them to take the stress while the other is barely stressed.

I thought of putting carbon fiber tape on my wooden spar caps. but the CF had better take all the load. It would not work well in combination with the wood.
 
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HumanPoweredDesigner

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If it were me I'd grab a pair of scissors and some thick water color paper. Paper gusets were good enough to last 70 years in my Aeronca I suspect they are good enough for a Piet.

The original Aeronca paper was called "fish" paper and is used for insulation in electric motors. Some gasket paper at the auto store appears to be the same material. Semi scientific testing indicates the water color paper soaked in glue, which is available just about anywhere, is an acceptable substitute.

You have to step back and see what the gussets do for the structure. Make up a sample test intersection with the same materials you plan to use, let the glue set, and then try to break it. If the stick for the rib breaks first the gusset is doing it's job.
I agree with your third paragraph. I've made some very strong structures with paper gussets. But they are not as strong as plywood for their weight. While your method works, I'm sure it was heavier than it needed to be.
 

Gnarly Gnu

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Get some plywood made up - 3 leaves of timber veneer glued together will give you 1/16" and is quite strong with the central layer running perpendicular. This is a simple job for a veneer company, ask them to use a waterproof adhesive also. Easy peasy.
 
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