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Plug in wing tubes How to

Old 12-28-2005, 04:21 AM
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Grasshopper109
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Default Plug in wing tubes How to

Hi every one,

I want to build a 1/4 scale space walker with plug in wings and was wondering how to put the tubes into a built up wing with about 75mm of dihedral at each wing tip.

Any suggestions would be great

Grasshopper
Old 12-28-2005, 08:49 AM
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Default RE: Plug in wing tubes How to

Grasshopper,

I did the same thing building my 86" W/S Druine Turbulent designed by Chuck Cunningham. I bought a wingtube and sleeves from Gator RC. I had to reduce the dihedral a bit to fit the tube in the wing, but it has not had a negative affect on the flight characteristics. The sleeve had to be located high in the wing at the root and dihedral was determined by required clearance at the outer end of the sleeve.

I built a center section of the sleeve into the fuselage. If you carefully locate the sleeve holes during construction you will have a straight square installation when fuselage is built up. I added some ply donuts to reinforce the sleeve. The wing sleeve clearance holes were cut oversized so that incidence/position could be set during fit-up. Lite-ply donuts were added at each rib that were tight fitting to the sleeve. I cut a complete doubler rib of lite-ply to fit tightly to the sleeve for strength and linking with the alignment tube to the rear.

The design of my wing located the spar far enough back that the tube could easily be located just forward of the spars. I located an alignment tube as far back as I could. This resulted in a good spacing between the two.

My bird weighs about 16.7#. I used a 1-1/4" aluminum main tube and a 1/2" alignment tube. I have seen no problems with the arrangement either in flight or the occasional rough landing.

You are welcome to PM me if you have any follow-up questions.

Good luck,

Bedford
Old 12-28-2005, 01:57 PM
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Default RE: Plug in wing tubes How to

The tubes need to either fit between the upper and lower spars and be boxed in to couple to those spars or there needs to be some well done structure to couple the tubes to the spars. The geometry of the space between the upper and lower spars and the dihedral needed as well as how far the tubing needs to extend into the wing will determine if it will all work. Either way the tube needs to be bonded well to the spars. Epoxy and microballoon filler is one method followed by a kevlar, carbon fiber or similar wrapping around the spars and tube at the root and near the end of the tube.

Another option is to go for a blade style of joiner rather than tubing. Since this type of joiner is a tall rectangle you can form it into whatever angle you want by cutting the blade from suitable tempered aircraft aluminium. Not just any aluminium. You'll want to get a proper alloy and heat treatment grade from someone that you can trust. Often scrap dealers will have suitable sheet. You're looking for the stuff that actually has the alloy and temper numbers printed on the metal. If that printing is not there then do not use it as it's likely just a soft general purpose alloy. Something like 1/4 inch 6061-T6 or similar would be my suggestion. You're looking for a structural grade of alloy that is not intended for complex forming and bending.

With a blade style system you just box in the spars with plywood front and back and cut away the portion of the ribs that block the new "tube" formed by the structure. The boxing really needs to be bound with Kevlar thread or something equally strong right by the root and where the blade ends. These two spots of the box will be the most highly loaded with the blade acting like a pry bar to split the spars apart. Within reason the longer the blade the less prying action there will be (leverage ratios and all that nonesense)
Old 12-29-2005, 12:43 PM
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Default RE: Plug in wing tubes How to

Bruce, I don't agree and many designs out there have the tube aft of the spar set. Mine happened to work out better forward. I do agree that between the spars is the cleanest structurally, but it can be problematic with dihedral. By moving the tube away from the spars (but very close) you set up a torsion in the wing based on the distance between the two centers. It is essential, then, the build the tube sleeve support with this in mind. Very good structural integrity between the sleeve and spar set at the root and again at the outer end. This torsion is not great and can be structurally overcome with some good basic construction. That said, I do not fly wild 3D.

Bedford
Old 12-29-2005, 01:27 PM
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Default RE: Plug in wing tubes How to

Actually I did mention about proper structure if the joiner is not located within the spar system but I can see how it could have been missed with all my wordiness. We're definetly on the same wavelength.
Old 12-29-2005, 02:24 PM
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Default RE: Plug in wing tubes How to

Wow thanks for the great replies,

My next question is weather it is possible to run the outer wing tubes parallel between the spars and have the inner tube bent in a v to the correct dihedral. Or will this make the tube too week?

regards Glenn
Old 12-30-2005, 01:45 PM
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Default RE: Plug in wing tubes How to

Bruce,

I read you right. I always have high regard for your comments on this forum.

Glenn,

If you go with the bent tube approach you gain a small amount of strength in the wing with the tube running parallel to the wing spars (assume that is your objective). The problem is that you loose a lot of the stength in the fuselage. With an unbent tube you can resist moment with a lever arm across the full width of the fuselage. With a bent tube (performs like two tubes butted together) you are resisting monent about half the fuselage length. Doubles the bending moment because you have half the moment arm.

If you want to continue in this direction, I would go with the blade approach Bruce described. You can offset one blade slightly forward of the other and run them nearly the full width of the fuselage. I think Byron's birds were built this way.

Bedford

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