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Succesful Geodetic Model, Finally

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StarJar

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I made a new model with slightly reshaped bulheads which solved the problem of breaking lattices when bending.
Some of you had questions or made suggestions which màde me think about how to explain exactly what I have here. This may be painfully boring with obscure details, but it all ties together to explàin exactly why it is the way it is now.
The formers have notches and the formers are cut out out of chipboard on à Sizzix Eclips machine from a pàttern made on DevFus, which is à newer version of Profili.
The notch pattern is actually for straight stringers, but I just ran the diagonal stringers through the notches diagonally.
This means there are intersections AT each bulkhead, and BETWEEN each bulhead. There are 27 notches on each bulkhead. If there were less than 27 notches the lattices would hàve steeper angles, and if there were more than 27 notches they would have shallower angles.
The notches are each deep enough for 3 stringers (lattices); two diagonal sets crossing each other, and one horizontal' or lateral set which are the outermost stringers, and last to apply. This allows for structural compression and tension, gives a more streamlined outer shape, and allows for fabric attatchment.
The fuselage is quite stiff tortionally after only 6 diagonal lattiçes are inßtalled, so by the time you have all 54 diagonal lattiçes installed it is incredibaly stiff. The adition 27 'streamlined' stringers add more strength.
On the full size plane, stringers will be cut from 1/4 inçh thick unidirectional plywood sheats special ordered from Home Depot.
There are 83 stringers total, with an everage length of about 10 feet. The stringers do not run on the first 15 inches of the airdraft because the firewall is 15 inches from the nose. they also dont run the rear 15" of the aircraft, because the tailpost and tailwheel spring are 15" from the rear of the 12 ft. long airplane. A spevial lightweight, less structural tailcone will be used there.
87 striners times 10 ft. is 870 feet. the crossection of stringers is .25x.25 or .0625 sq. inches. So the volume of wood for the stringers is 870x12x.0625 or 652.5 cu. inches.
To calculate the weght, a cubic foot (1728 cu. in.) of the wood weighs 30 lbs. ....652.5÷1728 is .377. .377x30= 11.3 lbs.
The bulheads- I haven't fugured the exact weight yet, but their total area with 1/4" plywood comes out to about 9 lbs.
So you have about a 21 lb shell including hot melt glue from a gun.
Below are two pictures side to side for a larger veiw.
This is a 1/4 scale of a planned ultralight flying wing.
That is the El Centro News, thanks for watching, lol.
IMG_20161120_164253_297.jpgIMG_20161120_164338_613.jpg
 

BBerson

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I haven't heard of unidirectional plywood. I have heard "laminated veneer lumber" that I considered for spars.
Will you cut 1/4" x3/4" strips?
The traditional is 1/8"x3/4" spruce strips for geodetic.
 

StarJar

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I haven't heard of unidirectional plywood. I have heard "laminated veneer lumber" that I considered for spars.
Will you cut 1/4" x3/4" strips?
The traditional is 1/8"x3/4" spruce strips for geodetic.
No I'm cutting them 1/4 inch square.
The unidirectional plywood is also called 'bendy' or 'raduis' plywood.
 

StarJar

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I'm not sure what it's density and strenth is because I haven't bought any yet. I have to drive 80 miles to pick it up, and I'm just going to order the sheats when I'm ready.
If it's a very light wood, thats ok, because there is tons of overkill, even though this structure has a light weight.
There are two uni plies so that gives it some advantage over solid sticks, regarless of species to prevent splitting.
The two plies also makes it possible to veiw for knots or voids.
 

BBerson

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I would research the peeled wood process. Seems like it isn't sold for structural use. Perhaps the peeling damages the wood fiber (just a guess). Also, check for waterproof glue.
 
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plncraze

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The company offers to send samples. You could test it per the ANC-18 standards. It would be interesting to see how modern glues hold up.
 

SpainCub

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Madrid, Spain
Pretty cool, I have been very interested in Geodetic designs for strength/weight ratios...

I've recently come across a very old pattern that albeit not Geodetic, it does leverage wood as nature fibber and Phenol-formaldahyde to make a very strong composite out of wood. https://www.google.si/patents/US1344634 (1937)

IT paces wood veneer on a 90 +45 0 -45 degrees angles to create waterproof structure in a mould. Basically, a natural composite, or in mould plywood :)

I always wondered If you used the process that got plywood mainstream (glue with a paper soaked phenolic resins) and created a plywood composite out of Balsa, what the strength to wait ratio would be like compared to say CF? :)
 

StarJar

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Pretty cool, I have been very interested in Geodetic designs for strength/weight ratios...

I've recently come across a very old pattern that albeit not Geodetic, it does leverage wood as nature fibber and Phenol-formaldahyde to make a very strong composite out of wood. https://www.google.si/patents/US1344634 (1937)

IT paces wood veneer on a 90 +45 0 -45 degrees angles to create waterproof structure in a mould. Basically, a natural composite, or in mould plywood :)

I always wondered If you used the process that got plywood mainstream (glue with a paper soaked phenolic resins) and created a plywood composite out of Balsa, what the strength to wait ratio would be like compared to say CF? :)
The advantage could also be in price, and the thickness is more anti- buckling.
 

plncraze

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I was talking to a woodworker about non-formeldahyde glue ply. I asked about water resistance and he told me not to let it get wet. One of the tests for aircraft wood I believe involves boiling the wood.
 

TFF

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Bendy ply is not structural. Makes cool shapes in the house but not strong. If you are going to need shaped bulkheads, you will need to press your own in forms.
 

StarJar

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Bendy ply is not structural. Makes cool shapes in the house but not strong. If you are going to need shaped bulkheads, you will need to press your own in forms.
Although bendy is not used on bulkheads, I can tell you are one with higher standards than the type of wood I've chosen for this design.
 

Aerowerx

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Although bendy is not used on bulkheads, I can tell you are one with higher standards than the type of wood I've chosen for this design.
I would be afraid of any plywood that was not guaranteed, unless you have X-ray eyes and can see the inside layers. Even if you test one piece and it passes, what about the next one? You don't want to be at 2000 feet and find out you made a bad choice.

IMHO anything from a big box store should not be trusted for aircraft. Solid wood is different, though, as there are no hidden layers and it is easy to grade it yourself. Even then, I buy mine from a full-scale reputable lumber yard and pick it out myself.
 

StarJar

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You guys are jumping in without reading the entire thread.

@Aerowerks. Ive soaked ply for s week then boiled it. da glue was still strong.
This is 2 ply. Thats good enough inspection for me.
The fuselsge has a g rating of about 15g's as shown.
The two ply also protects against freak splintering.
Too many plusses to condemn it without evidence or proof from testing, IMO. ymmv.
 

plncraze

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I was wndering how that would hold up to testing. I figured the glue is synthetic and would be much better than animal based glues. As long as you don't have many voids you should be in good shape. The geodetic builders in the thirties load tested their completed aircraft. If you do that prior to covering you will have good idea of the strength and stiffness.
 
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