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dihedral break in middle of center section

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raymondbird

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Hello all,

Want to convert my one piece spar design to three 8' pieces (tight building space) like a Mustang II. Could buy the plans but it is a straight 8' center section that doesn't look easy to put dihedral all in the center.
Anybody have any suggestions or know of any other design plans I could purchase with all the curve in the center section?

Thanks very much!
RayCS Spar.jpg
 

Hot Wings

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Not clear on what you really want to do - the pic is kind of confusing.
Do you now have a single 24 foot spar or a 2 piece spar with center attachments like the photo?
If it is a single piece spar why do you want to add dihederal? Is the per-plans plane lacking some kind of stability?
If there are plans available for this modification the quick and sure way is to just buy the plans and follow them.
 

raymondbird

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Not clear on what you really want to do - the pic is kind of confusing.
Do you now have a single 24 foot spar or a 2 piece spar with center attachments like the photo?
If it is a single piece spar why do you want to add dihederal? Is the per-plans plane lacking some kind of stability?
If there are plans available for this modification the quick and sure way is to just buy the plans and follow them.
My present design is a one piece spar with all the dihedral in the center. 6 degrees a side. The picture is a Mustang II center section, three piece design.
I like the Mustang design but just with all the dihedral in the center section. Is that possible?
 

Topaz

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Yes. Harder to build than simply adjusting the between-panel fittings of the three-panel design, but possible. Essentially it's exactly the same as if you had a one-piece wing and are simply adding panel breaks. The spar caps and shear web will continue through the dihedral break. The center panel will have a "bend" in the middle to create the dihedral.

This is for a custom-design airplane?
 

Turd Ferguson

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I get it, you want a three piece wing but you want the dihedral in the center of the center piece with the outer pieces bolting straight on to the center. Converting a straight center section to one with dihedral will be somewhat challenging as you'll have to ensure it can carry the design loads.

A Corby Starlet can be built with a three piece wing and all (a moderate amount) of the dihedral is in the center but it's a wooden wing so that probably won't be much help.

On most low wing airplanes, the wings bolt to a bulkhead and the spar does not pass through the cabin. That's how they set the dihedral. A Mooney has a one piece wing so that structure does pass through the cabin as does a few other production planes but I don't think you can get plans for those.
 

BJC

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One option is to split the center 8’ section into two 4’ sections, and splice it at the centerline with the desired dihedral.

That could be easy or difficult, depending on how it is attached to the fuselage.

There is a build thread here that has nice photos of a three piece spar being built. In that case, the center section spar caps are cut out of thick sheet with the curve built in.

See special ??

BJC
 

pictsidhe

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A centre break is going to need a redesign. Putting the break at the joints is popular for good reason! I'd probably start with a centre break one piece spar and add joints for the outer panels.
A centre break will put the web at the break in compression for +ve g, tension in -ve g. Aside from bending the caps, that is likely your biggest redesign consideration. Shear webs do not need to be continous through the break.
 
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TFF

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The Mustang II used the straight center so they could use the wing panels from the Midget Mustang without redesign of the whole wing. Teenie Toos and Jodels did it because the joint outboard of the center did not have to be as strong making the plane lighter. Somewhat less complicated to build.

Essentially you are willing to make the center as complicated as a Corsair for looks. I get the space need part. Build the center out like designed to 4 foot a side and make a break for outboard wing panels. It’s not going to be light as you will have redundant fittings, but it is the only way you can get it built, better than nothing.
 

raymondbird

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Yes. Harder to build than simply adjusting the between-panel fittings of the three-panel design, but possible. Essentially it's exactly the same as if you had a one-piece wing and are simply adding panel breaks. The spar caps and shear web will continue through the dihedral break. The center panel will have a "bend" in the middle to create the dihedral.

This is for a custom-design airplane?
Well, not quite yet but I guess it will be if I go ahead with this metal wing conversion. Big decision needles to say. It's been all Jurca 109 replica up till now but I just don't have room anymore to build a 24' wing and can't wait any longer. I love the "special" that BJC put me onto. That is exactly what I had in mind: 3 piece wing with all dihedral in the center. Will look into that some more.

Thanks so much all of you!
 

Topaz

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Well, not quite yet but I guess it will be if I go ahead with this metal wing conversion. Big decision needles to say. It's been all Jurca 109 replica up till now but I just don't have room anymore to build a 24' wing and can't wait any longer. I love the "special" that BJC put me onto. That is exactly what I had in mind: 3 piece wing with all dihedral in the center. Will look into that some more.
Ah, okay. If build-space is an issue, rather than redesign the wing you might consider putting a lot of effort into finding alternate build spaces. You really don't need the "big" space until you're ready to start the spar and assembling the wing, so all the ribs and fittings can be built first, stored, and then assembled at an alternate site. This could be a hangar you rent or sub-let (or borrow space in, if you can find a friend or a generous soul), space at a friend or associate's warehouse or shop or, in a pinch, even a rented ground-level storage unit with a portable generator to power tools and lights. All you need is some kind of lockable, enclosed, weather-proof space that's long enough for the wing and wide enough to work in. Get creative! :)

I'm not saying "don't" redesign the wing, but rather that there are other options to explore before you take that very large step. You might be surprised to find you can locate a good space very close to home, for little or no money. If you build all the "little pieces" for the wing first and then put them all together, you minimize your time in this alternate build space.

Just a thought.
 

pictsidhe

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Well, not quite yet but I guess it will be if I go ahead with this metal wing conversion. Big decision needles to say. It's been all Jurca 109 replica up till now but I just don't have room anymore to build a 24' wing and can't wait any longer. I love the "special" that BJC put me onto. That is exactly what I had in mind: 3 piece wing with all dihedral in the center. Will look into that some more.

Thanks so much all of you!
If the design you have is for single spar wing, your design challenge is breaking it.
 

rv7charlie

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Topaz raises a point worth considering. I have a couple of mech engineer friends to bounce stuff off, and I would be very hesitant to try modifying an existing spar design (self-preservation instinct grows stronger as I age). No way for us to know your exact situation, but most people would have less trouble (and expense) finding temporary space than completely re-designing a major component in an airframe. If altering your build *situation* is even remotely possible, I'm sure some of us could offer some ideas.
 

mcrae0104

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The answer will depend on how the center section attaches to the fuselage. Can you tell us more about that?
 

raymondbird

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It isn't that difficult to make a center section curve gradually just by curving the cap extrusions and riveting to a curved web. I did it.
Very interesting, so instead of vertical, you orient the extrusions flat so that they can follow the curve? How to rivet them to the web though when flat?
Cheers
 

BBerson

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Very interesting, so instead of vertical, you orient the extrusions flat so that they can follow the curve? How to rivet them to the web though when flat?
Cheers
Angle or T-bar extrusions can be used to build up a curved I-beam spar. Standard aircraft practice. The extrusion caps are not flat but will curve some if forced into a jig. Or, if needed can be bent some with a bit of practice.
 

mcrae0104

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Sure can, present design calls for 2 large bolts at the fuselage sides into a massive bulkhead.View attachment 103429
I just want to make sure I understand... you're building a metal wing to attach to a wooden fuselage?

If it's a wooden wing, just build the center section with the dihedral break like you would at the middle of any one-piece wood spar. Attachment stays the same. When doing the design, don't forget that there is an axial component along the spar due to lift and your shear web design will need to account for this.

If you're doing a metal wing, I think BJC has the ticket--split at the middle, and spliced together. With the two-bolt attachment, shear will be zero between the bolts (assuming the wings are loaded evenly) but bending moment will be at its maximum value between the bolts. Therefore the splice at the middle will need some attention to carry the moment, but you could treat it similar to the design of an ordinary wing panel joint (heavier here because of the high moment) or you could make the caps using built up 1/8" curved "straps" (RV style) or by curving the angle as BBerson suggests.

You might also look into @Will Aldridge's SpitSairWulfStang project--it had a curved spar for a in inverted gull, but I don't remember the material or details.
 

Will Aldridge

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I essentially borrowed the WAR replica Corsair wing structure which utilizes a box beam main spar with solid rear spars.20180219_222320.jpg

These are the outer panels. I can't find pics of the center section now but each section is 8 ft. The center section caps are 1/8" thick strips laminated to make the curve necessary for the wing and are 2" x 2" and the ply shear webs in the center section are 1/8" thick. The outer panel top caps are 2" x 2" at the root tapering to 3/4" x 3/4" at the tip with 1/16" thick ply for the shear webs. There are inter costal supports not seen in the photo. The sections are joined together by .090 4130 steel fittings. It's essentially the same basic design as the KR2. The way the wings are joined with the steel fittings makes changing the dihedral fairly easy. Obviously there are probably limits to the amount of dihedral you could add but they would be extreme for most designs.
 
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