In sleeve:yes.....outsleeve???

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David Teahay

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In sleeve tubes help to reinforce high stress areas in wing spars,my question is,is there anything like outsleeve tube? Isn't it better to just put a sleeve tube on the outside of the spar rather than cutting the spar then inserting the insleeeve tube?
 

lr27

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If you don't need the tube to be the same size in the reinforced area, then it would be stiffer and stronger to put the "sleeve" on the outside. However, I think a lot of times, the tube that's getting reinforced may be the leading edge of the wing. Putting the "sleeve" on the outside changes the shape of the airfoil and requires a slightly different rib.

By the way, tubes don't make very good spars. Spar caps with shear webs will be stiffer and stronger in bending. An example would be an I beam.
 

Aerowerx

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Do you actually cut the tube and insert the reinforcement?

Wouldn't that make a weak spot in the outside tube, negating the reinforcement?
 

Dan Thomas

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Do you actually cut the tube and insert the reinforcement?

Wouldn't that make a weak spot in the outside tube, negating the reinforcement?
Exactly. Sure wouldn't want to cut it. You'd end up with a weaker spar overall, since the sleeve would be smaller. Dangerous.
 

wsimpso1

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QUOTE=David Teahay;452405]In sleeve tubes help to reinforce high stress areas in wing spars,my question is,is there anything like outsleeve tube? Isn't it better to just put a sleeve tube on the outside of the spar rather than cutting the spar then inserting the insleeeve tube?[/QUOTE]

David,

Any place you have a metal tube in a structure and you want to choose the tube sizes, you start with the load cases derived from the flight envelope. Then for each of the cases (you will have a minimum of four (lg limits at Va and Vne), probably four more at full flaps, maybe others. Each of those cases will produce a load set (axial load, bending load, and a torsional load) on every tube. You select a first guess tube for each application, and check it on each load case. You can calculate the stresses and direction of stresses for each load type, and by superposition search out the worst stress state in case, plus check for buckling and crippling. Record your lowest FOS for that tube. If you are working in metal tubes, and it has FOS below 1.5, it will need to be either bigger OD or thicker wall or both. If the FOS is much above 1.5, you might be able to use a thinner wall or a smaller OD. Pick the lightest one that gives FOS above 1.5 everywhere.

Now making a tube diameter and/or wall thickness bigger can be done by putting one tube inside another. I again urge you to try out the range of tubes that work and pick the lightest combo that makes enough strength. The job is not to make the strongest part, it is to make the lightest part that does the job.

By the way, this fits solidly in the category of "questions that should be preceeded by some time in the beam theory section of a mechanics of materials text book".

Then there is another case where you might place one tube in another - repair. Say a fuselage tube gets bent and it has a couple little cracks. You are not going to straighten that tube and go flying. Or you find corrosion . Either way, you will cut out the damaged section, replace it with new tube, and sleeve it. Several ways to skin this cat. Usually you will angle cut or fishmouth the tubes and weld them, but getting the alignment right and strongly welded is usually a littlle iffy, so we also sleeve the joint to hold the new butt welded joint in alignment. The sleeve is usually internal and attached to the outer tubes with rosette welds.

Why internally? We presume that the original tube was strong enough and stiff enough for normal use, so it does not need to be bigger and stronger, but it does need to be supported to keep it fairly straight during the welding. It will also need a little bit of support against buckling right at the weld, which is also where you are likely to have the repaired tube be just a skosh crooked. So the internal sleeve makes it all into a sturdy repair. You can actually install this repair in between cluster welds of tubes in an existing structure by slipping the internal tubes inside the main tubes, and manipulate the internal tubes to position before you start welding - the holes rilled in the outer tubes for the rosette welds come in really handy for scooting the internal tube around. If the whole thing is then wrapped in fabric, the only visible blemishes are the welds themselves.

Think your way around applying an external tube... You can do it, but remember - no grinding down or polishing structural welds to make the sleeve run over it, so you might have trouble getting the main tubes solidly welded AND able to take the external sleeve. And it will stand out like a sore thumb on a fabric covered ship. You might have to apply an external sleeve in two or even three pieces to make it work - that is no longer a reinforcing tube, that is now finger straps.

Billski
 

lr27

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Billski:
My guess is he was talking about aluminum tubes without welding, but I could be wrong.

Do you take any special precautions about corrosion between the inner tube and the outer tube after welding?
 

Aerowerx

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I have seen some plans where a smaller tube is placed inside the larger tubular spar at some attachment point.

Like where struts are attached. Usually with a bolted bracket. My impression has been that you insert the smaller tube at the end and push it in until it reaches the correct location.

Not 100% sure of this, but designs like the AffordaPlane come to mind.

Edit:
Just checked. A snip from the AffordaPlane plans....

Capture.jpg
 

proppastie

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In sleeve tubes help to reinforce high stress areas in wing spars,my question is,is there anything like outsleeve tube? Isn't it better to just put a sleeve tube on the outside of the spar rather than cutting the spar then inserting the insleeeve tube?
I would think if you are talking about new design and new construction the sleeve on the outside would be stronger than on the inside if they are all the same wall thickness. It might help to add some more detail as to what you are trying to do.
 

Jerry Lytle

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In my hanglider days I measured where the end of th tube should be, inserted and pushed/tapped unti properly located and put in a single pop rivit to hold it in place. The main outside tube was the main load member, the inside tube wlas local reinforcing where needed.
 

wsimpso1

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Billski:
My guess is he was talking about aluminum tubes without welding, but I could be wrong.

Do you take any special precautions about corrosion between the inner tube and the outer tube after welding?
On the first question, he did not specify material in use. The material selected does not change the process. You still size based upon material strength vs stresses produced and select the lightest solution that makes suitable strength.

After welding in a splice to repair a steel tube structure, of course you corrosion protect. Convention is you sand blast the outside and prime with epoxy primer. The inside is protected by wetting the inside with linseed oil or other anticorrosive oil. Usually, you make sure all tube intersections have a hole drilled to allow the interior to communicate throughout. Then you drill a hole someplace benign, fill with oil, put a sheet metal screw in the hole, and rotate the assembly in all three axes. Drain and replace the screw. Many folks will oil the parts prior to welding, but we know that the oil will burn off in the vicinity of each weld, so it still requires treatment after welding.

Billski
 

TFF

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Lots of ultralights will slip tube within a tube for reinforcements at wing attach or struts. Acting as doublers. Aircam does. I think the Kit fox does also. You do have to know stresses on how far out you need to go and if you want to taper the ends inside the tube. Outside tube would make covering tough to do and not pretty.
 

PiperCruisin

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Lots of ultralights will slip tube within a tube for reinforcements at wing attach or struts. Acting as doublers. Aircam does. I think the Kit fox does also. You do have to know stresses on how far out you need to go and if you want to taper the ends inside the tube. Outside tube would make covering tough to do and not pretty.
The Avid had an insert (extruded, custom I beam...I assume Kitfox was similar) about mid-span where the strut attached. They also used a steel doubler on the inside at the root attach point for bearing support.
 

TFF

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The Aircam changed theirs to a more normal insert. I made the owner of the Aircam I mess with take and have his updated. The tube within a tube was working and wallering out the rear root mount hole. Engine is right there for vibes. I did not have the time to pull the wings and mess with it.
 
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