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Carbon spar with diedral in middle -Jodel

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opcod

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Hi

I have since a long time a pretty big question that i'm not sure. If i whant to build a wing straight, but at the 2/3 of the wing(from the fuselage) you got a diedral of 5degres. Exactly like a Jodel aircraft.

So if we use a Jim Marske method with the carbon rod, it's pretty easy for a straight spar, but if i whant a diedral like this (the picture) how can it be possible. Like the whole wing can be made with a D-cell with the I beam all in carbon, but at the joint, is making a fitting with pins, like the old Corsair or other Grumman or the ww2 era with the flip wing could be interesting...

Because, if we bend the carbon rod, maybe just at the stress test, a delamination might occur before the 6g.. Or making a joint at the diedral it will maybe request like 8-10 layer of fabric to sustain the charge... But again, the carbon rod will be cut, so it maybe become a stress area that may occur a failure.
So if you have some idea how to manage this one, it will be welcome.
Thanks.
 

Starman

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If it's a box spar put a really strong bulkhead inside the spar at the joint, also a stronger rib in the D cell. A stronger shear web at the joint can help transfer loads.
 

autoreply

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So if you have some idea how to manage this one, it will be welcome.
Well, if a fluently bent up wing is ok as well, why not do that? I'm referring to the 787/A350 tip style. Given the small diameter of the rods, you probably can get away with such a large bending radius.

If a sharp bend is really required, well, that's a major design challenge. You're introducing all kind of forces and moments into the sharp bend and you have to evaluate all of them.
 

Careca

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Hi

How is your french?
The Dyn’aero guys are developing something similar to what you pretend, it’s the DR-2 Phoenix and it’s basically a Robin with mixed construction, wood and composite.

Présentation
DR² "PHENIX"

 

wsimpso1

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Graphlite rods are routinely rolled onto spools for shipping. Basic mechanics will give you the stress in the rods at a given bend radius. Designing the wing for a fairly gentle bend would allow you to use graphlite - just remember that some of your strength is already occupied in the bend, so the your structure has to live within the strength that remains after the bend is installed.

Billski
 

Dan Thomas

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The Jodel's designers did that to their wing to get the central part of the spar seamless, keeping it as light as possible and moving the angled (glued) joints out to where the loads are smaller. You don't have to do that with many other materials, especially if you want the wings removable. Seems to me Falconar had a version of the Jodel (the F-11? F-12?) that had the dihedral break in closer to the fuselage and had steel fittings to allow wing removal. Of course, any such design adds a terrific amount of weight, with all those fittings and the need for reinforced wood construction at the fitting bolt-through points.

The Jodel's spar is a box section, around eight inches deep and about 10 or 11 front-to-back, and it carries all the lifting, landing, drag and torsion loads. There is no other structure in the wing besides ribs and two false spars for aileron attachment. That spar is the biggest part of the whole project and is famous for its enormous strength, though mine is now well over 40 years old and while the wood is fine, urea-formaldehyde glues are known to lose some strength with age and I sure wouldn't pull the 6 Gs it was rated for.

Dan
 

opcod

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Hi

So if we took almost the same concept as the KR2, with the wing spar and in the middle you put
2 attach point to fit for an outboard spar : So a diedral could be easily acheivable then ?
KR-Super2

All explain on that webpage as the first picture. And you also see they use carbon spar cap also on top and bottom.
Is that design is working ok because it's a small wing ?
I mean, if i put an outboard of almost the same as them of 70inch from the junction, does the
main spar (the straight one) need to be not too long ? Or it's mostly all the fittings to handle the load will become quite heavy.

*And for sure, that's for a removable wing. 4 small sections that could be handle and move around more easily.

thanks again
* And yes, my french is quite perfect rather than the english, merci pour le lien .. And sorry for my english mistake.
 

wsimpso1

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Don't worry over your English - it is way better than my French.

You can form the wing in just about any method you want with Graphlite as long as you use a fairly large radius in the bends. The graphlite has a certain amount of strength according to its suppliers. The bend uses up some of it according to the following relation:

sigmax = E*t/(2*rho)

Where sigmax is stress in the long direction of the graphlite rod, E is Young's Modulas of the Graphlite, t is the thickness of the rod, and rho is the radius of curvature as the rods are used. Small radius sets the static stress in the rods higher, larger radius sets it lower. Whatever stress that is induced in the rod in bending has to be added to the stresses as you design the structure.

In every design where they play with varying dihedral, there are reasons, and they are usually somewhat detrimental to the aerodynamics of the subject airplane. In general, you want one bend per side, and at the fuselage. Also, the lightest wing arrangement is gnerally where a one piece wing is bolted to the fuselage with four bolts. Next best is the glider arrangement, where each wing attaches to the other, and to the fuselage. Still can be done with four bolts. The next arrangement is a stub wing (center section) that is permanently built in, and then with the outer panels overlapped and bolted. This adds some weight... Straight (no dihedral) section, and then a lot of dihedral on the outer ends is used in a few airplanes for specifc reasons that I would not even consider in an all composite wing.

Billski
 

rtfm

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sigmax = E*t/(2*rho)

Where sigmax is stress in the long direction of the graphlite rod, E is Young's Modulas of the Graphlite, t is the thickness of the rod, and rho is the radius of curvature as the rods are used. Small radius sets the static stress in the rods higher, larger radius sets it lower. Whatever stress that is induced in the rod in bending has to be added to the stresses as you design the structure.

Billski
Phi,
im not sure i understand this correctly, so if someone could look over my shoulder on this, that would be great.

E for Graphlite = 21,000,000
t = .092 (inches)
rho = 18 (inches)

plugging these values into the formula gives me 53,666

Question: If this is the pre-stress in the rods due to bending it, what do I do with this number? Subtract it from the tensile strength of the rods?

If so, with a tensile strength of 320,000 psi, this hardly makes a difference. It makes SOME difference, but relatively little.

Am I on the right track with this (computationally and logically)?

Duncan
 

autoreply

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The problem is in the shear web. You're putting massive compressive loads on it. That starts to create problems with peel, compressive (vertical) buckling etc. The pre-stresses in pultrusions are usually too small to be relevant.
 

Doggzilla

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It would be a lot better just to have one joint in a carry thru wing. Not only does it reduce the complexity, but the stress can be vastly reduced because the force is already be transmitted into the fuselage.
 
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