Joining Al tubes

[Old Koreelah]

I seek advice about connecting two aircraft grade aluminium tubes which will serve as the leading edge of my flaps. For simplicity and added strength, I am making the flaps in one piece, so the connected tubes will be 4.5m long. At the centre the overlapping sleeve, about 500mm long, will be both glued and riveted over the tubes it is joining. It will also take most of the torque loads from the flap actuating lever.

 

I have the material ready to do the job and feel that it may be wise to avoid a rigid strong point at the overlap, in case it leads to stress fractures. The two obvious solutions are shown in the attached picture; to "bevel" the very thin outer tube at the join, or (my preference) to "scollop" the edge with smooth curves, so that a single stress line cannot develop. Any suggestions?

 

Lyle

 

[ATTACH]14970[/ATTACH]

 

 

[old man emu]

Lyle,

 

Your picture did not come up. Please post again with the photo as an attachment.

 

OME

 

 

[rgmwa]

Haven't seen the photo, but understand that you want to avoid a sharp transition in stiffness at the end of the sleeve. Best would probably be a long taper but as the material is thin, the taper would be very short. My suggestion, and that's all it is, would be to consider cutting a series of equally spaced V's (like deep serrations - maybe 20mm deep?) with rounded and deburred ends and `valleys'. and with an internal angle of around 20-30deg. This will transition the stiffness over the 20mm length.

 

rgmwa

 

 

[Yenn]

Is this tube joining the 2 flaps and also acting a an actuator? If it is I would assume the main loads would be torsional, and the rivets would take that load. Why use glue, which would make repair in the event of damage much harder to do?

 

 

[Old Koreelah]

Is this tube joining the 2 flaps and also acting a an actuator? If it is I would assume the main loads would be torsional, and the rivets would take that load. Why use glue, which would make repair in the event of damage much harder to do?

Because, like the Irishman, I want be sure, to be sure, to be sure. If my rivet work is dodgy, then a metal epoxy bond will ensure nothing works loose over years of use. (If I need to dismantle epoxy joins, heat will do it)

 

 

[Old Koreelah]

[quote="rgmwa, post: 176269"]Haven't seen the photo, but understand that you want to avoid a sharp transition in stiffness at the end of the sleeve. Best would probably be a long taper but as the material is thin, the taper would be very short. My suggestion, and that's all it is, would be to consider cutting a series of equally spaced V's (like deep serrations - maybe 20mm deep?) with rounded and deburred ends and `valleys'. and with an internal angle of around 20-30deg. This will transition the stiffness over the 20mm length.

 

rgmwa

 

Thanks for the feedback. I followed the tutorial but my pic did not load. Damn computers. I could modify my "scollops" so they are like your deep V serrations, as long as all edges are smoothly curved.

 

 

[Old Koreelah]

Lyle,Your picture did not come up. Please post again with the photo as an attachment.

OME

Sorry OME, I followed the tutorial which seems to refer to a previous incarnation of this page setup, but it failed to load.

 

 

[old man emu]

S'OK

 

OME

 

 

[Pilot Pete]

Try resizing the photo. Right click on the photo you want to upload, click on edit, click on resize in the paint program, click on pixals, and change to about 640 x 480 for a portrait photo or the other way round for a landscape orientated photo. When you close that program say yes to saving the photo. It will now be useable to upload into the forum.

 

 

[Old Koreelah]

Try resizing the photo. Right click on the photo you want to upload, click on edit, click on resize in the paint program, click on pixals, and change to about 640 x 480 for a portrait photo or the other way round for a landscape orientated photo. When you close that program say yes to saving the photo. It will now be useable to upload into the forum.

Thanks Pete for the attempt to help, but I only use Macs, which normally handle graphic with ease. I cropped the JPEG to 25KB so it should load in an instant. I have not had this problem with other sites.

 

 

[Old Koreelah]

1. Click "Settings" in the top right of the site header (Can't see this; I must be in the wrong page, or do pages look different on a Mac?
    
    
   
2. Click "General Setting" in the left menu bar on that page that is displayed
    
    
   
3. Scroll down to the bottom of the displayed page and with the option of "Enhanced Attachment Uploading:" click "Enhanced Attachment Uploading off"
    
    
   
4. Click the "Save Changes" button on the right of the page
    
    
   

 

 

3. Adding An Attachment To Your Post

 

When creating a new thread or post you will see the "compose" form that has a Title field, Formatting Toolbar, Entry box for typing, Smilies (click one to add it into your post ) and more.

 

In the Formatting Toolbar you will see a Paper Clip with up/down arrows: Not found either.

 

 

[Deskpilot]

Lyle, to make an informed decision we need to know the tube diameters and wall thicknesses.

 

 

[Old Koreelah]

Lyle, to make an informed decision we need to know the tube diameters and wall thicknesses.

Thanks, DP, the tubes are 2024T3; the inner is 1.5'' dia. with 0.035" wall; the outer is 1+7/8" with 0.35" wall.

 

 

[Deskpilot]

Lyle, you sure they're the correct sizes? 0.35" is a pretty thick wall thickness. Almost 10mm, and there's going to be a pretty big clearance twix the 2 tubes.

 

 

[pudestcon]

Lyle, you sure they're the correct sizes? 0.35" is a pretty thick wall thickness. Almost 10mm, and there's going to be a pretty big clearance twix the 2 tubes.

try 0.035" dp, I reckon a typo is involved eh?

 

 

[Pilot Pete]

Why not slip a piece of solid material in the smaller tube,slide the larger over and fix with 2 bolts 90 deg apart.

 

 

[Deskpilot]

Bolt or rivet, you need a sliding fit for a good mechanical join. This means, no slop, but then no pressure needed to push the 2 together either. The sizes you are giving leave way too much play to form a sound joint and therefore the rounding or tapering the inner surfaces of the outer tube are a mute point at this stage. For what it's worth, I would opt for a gradual arc bringing the wall thickness to about half it's original size and being about 10/15 times as long as it's reduction size. Does that make sense? eg. a 0.5mm reduction in wall thickness over a length of 5 to 7.5 mm. Just make sure there are no hard edges at the start point inside the tube. This will become a wear point if any.

 

 

 

[Old Koreelah]

Lyle, you sure they're the correct sizes? 0.35" is a pretty thick wall thickness. Almost 10mm, and there's going to be a pretty big clearance twix the 2 tubes.

 

 

Sorry for the typo DP, the tubes are 2024T3; the inner is 1.5'' dia. with 0.035" wall; the outer is 1+7/8" with 0.049" wall.

 

(Gawd I don't understand these archaic measurements; give me a few microns any day...)

 

 

[Deskpilot]

I hope I'm wrong but I've calculated a 3.5(179)mm gap all round your inner tube. I'd suggest you look for something around 0.5mm

 

Although I was raised in the UK with Imperial measurements, it is a damn sight easier to use the metric system.

 

 

[Old Koreelah]

I hope I'm wrong but I've calculated a 3.5(179)mm gap all round your inner tube. I'd suggest you look for something around 0.5mmAlthough I was raised in the UK with Imperial measurements, it is a damn sight easier to use the metric system.

Thanks DP, I learned both metric and imperial in a little rural NSW school in the 1950's- must have had a forward-thinking teacher!

 

I already have the two tubes, and the larger one fits pretty snugly over the long inner tube, with just enough space for some epoxy metal glue. I have not been able to upload my pix, so a description: If the ends of the overlapping sleeve are straight, then I fear a stress line could be established. If I "scallop" the ends of the outer joining sleeve tube to a continuous S-shape it should distribute stresses over a larger area. Any comments welcome.

 

 

[pudestcon]

Would I be correct in surmising that the stresses on the leading edge of your flaps here would not be that great, and therefore the stress line you speak of OK would be minimal? I imagine most forces acting on this component would be torsional, therefore the fixings (bolts and/or rivets?) would be taking most of the load, and that in shear.

 

Pud

 

 

[Old Koreelah]

Would I be correct in surmising that the stresses on the leading edge of your flaps here would not be that great, and therefore the stress line you speak of OK would be minimal? I imagine most forces acting on this component would be torsional, therefore the fixings (bolts and/or rivets?) would be taking most of the load, and that in shear.Pud

Yes Pud, that sound right. With hinge-points offset like a Jab, the flap is rotated thru about 37° and also pushed and pulled thru an arc by two actuating rods inside the fuselage.

 

 

[Old Koreelah]

Bolt or rivet, you need a sliding fit for a good mechanical join. This means, no slop, but then no pressure needed to push the 2 together either. The sizes you are giving leave way too much play to form a sound joint and therefore the rounding or tapering the inner surfaces of the outer tube are a mute point at this stage. For what it's worth, I would opt for a gradual arc bringing the wall thickness to about half it's original size and being about 10/15 times as long as it's reduction size. Does that make sense? eg. a 0.5mm reduction in wall thickness over a length of 5 to 7.5 mm. Just make sure there are no hard edges at the start point inside the tube. This will become a wear point if any.[ATTACH=full]14989[/ATTACH]

Thanks, DP, that's interesting and makes sense having the outer sleeve taper away from the inner one.

 

 

[djpacro]

I don't know the aeroplane type or any details of the flap design but I would expect such a leading edge tube to carry shear and bending as well as torsion. It seems to me that it would be worth doing an appropriate (but simple) engineering analysis and using standard design concepts.

 

You should get some good advice at http://www.eng-tips.com