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Made a geodetic (full wrap) fuselage model

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Aerowerx

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Is it flat-wrappable?

I would be tempted to wrap it with 1/16th ply (if it was full size, that is).
 

Dana

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The geodetic structure gives much of the stiffness you'd get from a full rigid skin, be it plywood or something else. Conversely, with a full rigid skin the geodetic would be largely redundant; you wouldn't need much more than perhaps a few longitudinal stringers to stiffen the panels at some points.

Dana
 

JamesG

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What about semi-monocoque (geez I hate spelling monocoque)? Where your "rigid" skin is just is thick enough to resist wind pressure and the geodetic stringers are scaled appropriately? The example that comes to mind is the hull of SpaceX's Dragon spacecraft:

 

StarJar

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Thanks guys.

The geodetic concept or idea (I think) is to use a thicker material (1/8") than plywood skin, because 1/8" resists buckling more than the 1/16" skin.
It is still much lighter. Last night I figured that a 30ft, UL geodetic wing would use only about 6 lbs. of strips, top and bottom, to resist twisting on a cantelever wing.

I learned 4 things from this model:
1. Interlacing at the top and bottom, to make a symetrical outer layer creates some extra bending, that is hard for the strips to handle without snapping.
2. Compound curves can be formed, but they have to be mild compound curves.
3. The structure is vey light and strong. I want to do full-scale load testing, to see what works and what doesn't for things like strip attach-points, and strip spacing.
4. Fabric strips will be neccessary, because there are small irregularities in the bent strips. They don't all bend alike.
 

bmcj

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Length 27" weight 1.3 oz. Very rigid with only 20% of joints glued!View attachment 38945View attachment 38946View attachment 38947
Very cool !!! ...but how are you going to fit in it?



What about semi-monocoque (geez I hate spelling monocoque)? Where your "rigid" skin is just is thick enough to resist wind pressure and the geodetic stringers are scaled appropriately? The example that comes to mind is the hull of SpaceX's Dragon spacecraft:

Well, DUH !!!! Full skinning is not really optional in a space capsule! :gig:

(Seriously, though, you came up with a great example to illustrate your point.)
 

Aerowerx

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The geodetic structure gives much of the stiffness you'd get from a full rigid skin, be it plywood or something else. Conversely, with a full rigid skin the geodetic would be largely redundant; you wouldn't need much more than perhaps a few longitudinal stringers to stiffen the panels at some points.

Dana
From what I was just reading, a geodesic structure covered with a solid skin would still be lighter than an equivalent strength monocoque.

I was just reading about one design from the 1930's where the designer said you could twist the fuselage 90 degrees before it would fail. There is something about having two layers of opposite spirals that make it stronger than a single skin.

Besides, I was not thinking of the thin ply providing all the strength but being just a smooth outer skin
 

FritzW

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So was your fuselage from model airplane plans or is this a scale model of the StarJar Super Sport?

I gotta tell you, my feeble mind filled with a whole lot of ideas when I saw those pictures;)
 

StarJar

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I been wanting to make a cantelever wood ultralight. Actually with long taperred wings. The next step is playing with wing. I know i want carbon caps, and I think everthing else will be wood.

The model started from a scale RF-4, model plans, and then i shortened the nose and tail a bit. And rounded the rear bulkead bottoms, to try the wrap.;)
 

FritzW

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My current "flat" geodetic UL effort seems like weak tea now... I wonder if the full wrap method would work with an AirBike sort of UL? ...hummmm

I'm looking forward to what come up with from the wing.
 

StarJar

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My current "flat" geodetic UL effort seems like weak tea now... I wonder if the full wrap method would work with an AirBike sort of UL? ...hummm
I forget what the Airbike is:ponder:, but it seems to me, everything has to be like an egg shell as much as possible.
I think there are a lot of subtle advantages that add up. The rear oval is less area, for aero, weight and wallet.
I used a larger angle than the normal 45. It still seems strong as hell!
I want to make a cheap full size one, to see where it breaks, when you load about 500 lbs on the tail!

Speaking of wallet, it seems like pine or cedar would work well, to bring the cost down.
 

Pops

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All of the geodetic strips for one wing panel weights 5 lbs and 1 oz.


Dan
 

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ultralajt

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My opinion, after reading the therad:
Nice build. Not perfect, but good enough for test. Covering with modeling heat shrinkable covering film will reveal the structure, so tiny longerons over the geodetic structure will help to get streamlined body and covering will be easier to apply.

Covering geodetic structure with a solid skin (plywood) is nonsence. If stucture is covered with solid skin, one need just to prevet its buckling by placing ribs (fuselage formers) and longerons at apropriate distances each to other. Geodetic structure resist both bending and torsional loads on the fuselage. Why then covering it with a solid skin, that will accept that loads instead. Even if one say that both (geodetic structure and solid skin together) will be stronger than each of them alone, hence greater combined strength, it is very hard to calculate loads and stress in such structure and do proper dimensioning of them.
Vickers Wellington WW2 bomber was geodetic structure, covered with fabric over some longitudinal (non structural) strips.
Mosquito, also WW2 bomber, was wooden, but solid sandwich skin (plywood/balsa/plywood) with sparse longerons and just a few load accepting fuselage formers.

I believe that geodetic structure is too complicated and brings no benefit in comparision to other more used technologies to build wooden aeroplanes.

Mitja
 
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