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Anybody ever witnessed an aluminum wing joiner tube fail?

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Anybody ever witnessed an aluminum wing joiner tube fail?

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Old 04-20-2018, 09:05 PM
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rustyrivet
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Default Anybody ever witnessed an aluminum wing joiner tube fail?




Yep... forgive me for having posted this in the other RC website too, as I want to reach as many experienced plane guys as I can;

I'm getting ready to build an old 11.5 pound 95" Sr.Telemaster. The kit was designed with a one-piece wing and has a steep 8 dehedral angle which will only allow me to fit a 3/4" O.D. sized aluminum tube into it. I'll have the outer joiner sleeve sandwiched with epoxy firmly between the upper and lower 1/2" x 3/8" wing spars, and I'm not worried about the tube breaking out of the ribs. But I am more concerned about it breaking or bending in the center. The tube I have on hand is an aluminum flag pole with a .030 wall. Can this tube handle stress of an occasional roll or loop of a big 95" winged Tele? I could buy another 3/4" aluminum tube with a .050 wall for $18 but don't know if that is overkill & unnecessary. Being I'm not an engineer, I don't know how to calculate the stresses that this tube will take right there in the center wing joint where it should be most vulnerable. (if it's vulnerable at all) If you try to bend this flagpole on your knee, it's pretty darn strong.....and is why a large flag in a strong wind doesn't bend or break it all week long. But then again, a flag is not an 11 lb Telemaster doing loops.


Has anybody ever witnessed an aluminum joiner tube on a big plane crack or bend from stress?


This is the older kit with a one-piece wing that I'm building.
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Old 04-21-2018, 09:04 AM
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Steve Collins
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I think I would try and find a carbon fiber tube.
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Old 04-21-2018, 10:53 AM
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Originally Posted by Steve Collins View Post
I think I would try and find a carbon fiber tube.
Thanks. But your brief input doesn't say much so I'll just stick with aluminum. Unless somebody with a lot of experience can tell me exactly what size carbon fiber tube will work, it is something else I would be guessing at..... at twice as much cost.
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Old 04-21-2018, 12:00 PM
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Here is a link to the supplier of all my models that I design:
Large Carbon Fiber Tubes
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Old 04-21-2018, 12:52 PM
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Originally Posted by ByLoudDesign View Post
Here is a link to the supplier of all my models that I design:
Large Carbon Fiber Tubes

$50 to $70 for a 4 or 5 foot length stick of 1/2"OD Carbon Fiber tube when I only need 24" is too rich for my blood and my 1991 Telemaster kit that I bought in the classifieds for $180. Maybe I can order a 24" stick on Ebay?? There seems to be plenty of it there.

In your experience what size OD and wall diameter Carbon Fiber tube should I be looking at for this project as I have described it? Are they all the same on Ebay when coming from China?......or do I have to be careful what I buy? Most of the ARF kits are made in China and I'm sure where the tubes are coming from too. The tubes from there seem to work when flown in the aerobatic models.
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Old 04-21-2018, 04:29 PM
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Rusty,
I suspect that your flagpole aluminum is most likely too soft an alloy to work safely. Where in Houston are you located? I live in Seabrook and am willing to assist in any way I can. I may even have some tubing that may work.
My e-mail is tcrowson@flash.net
Tas
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Old 04-21-2018, 07:37 PM
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If you have doubts just add some wing struts and you won't have to worry about it.
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Old 04-21-2018, 11:13 PM
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Originally Posted by tcrowson View Post
Rusty,
I suspect that your flagpole aluminum is most likely too soft an alloy to work safely. Where in Houston are you located? I live in Seabrook and am willing to assist in any way I can. I may even have some tubing that may work.
My e-mail is tcrowson@flash.net
Tas
Yes, after doing more thought and research, I've decided against the 3/4" flagpole stuff as being too risky. I will be using 3/4" T6 6061 grade tubing with a minimum .050" to .058" wall thickness. I can get the 3/4" .058 wall alum tube on Ebay for $16 shipped. But you can really feel the difference in weight between a .050" wall and a .058 wall. I'm still hunting down a ..050" or .053" walled T6 pipe. I think it's plenty strong enough compared to my .030" no name flagpolestuff.

That's nice of you to offer. ....Mighty kind of you. I'll contact you if I can't locate what I think I need. Thanks.

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Old 04-21-2018, 11:25 PM
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Originally Posted by Chad Veich View Post
If you have doubts just add some wing struts and you won't have to worry about it.
Yes....that would kill 2 birds with one stone, I suppose.

I was already planning on adding a fine wire brace of K&S piano wire on the underside of each wing half anyway....because this old style Hobby Lobby wing does not have the same structural strength of the newer and stronger Hobby Express kits of more recent years. But yea.....I might just as easily put a solid strip of aluminum there in place of the K&S wire to make formal struts and take a load off of the alum tube joiner in the process. Thanks for the suggestion. Food for thought.
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Old 04-22-2018, 10:23 AM
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Question:

Is there any reason I couldn't double the thickness of the kit's 1/4" x 1" dihedral ply brace to 7/16" thick and use that as a removable wing joiner?

It could slipped into place and boxed in between the 3/8" thick upper and lower pine spars. Then the spars would be reinforced with shear webbing on both sides to prevent the brace from pushing out the top of the spar. The 7/16" thick ply brace will weigh 110 grams and less then then aluminum tube and sleeve too.
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Old 04-22-2018, 04:37 PM
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Rusty,
There is no reason you cannot use a ply brace wing joiner enclosed in a box structure. The Telemaster has lots of lift so weight should not be a major concern. Whichever route you go solid wing struts are a good idea. The dihedral angle could be decreased somewhat without significantly affecting performance.
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Old 04-24-2018, 11:04 AM
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My thought is it you're going to go with thicker ply for the joiner, I'd make it out of aluminum and make it longer than the ply part that came with the kit. It will be lighter and stronger than a ply piece would and won't be subject to rotting as ply can be. Your choice of 6061-T6 should be plenty strong thought, if you're really going to stress the wing, 7075 would be better still
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Old 04-24-2018, 11:21 AM
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First of all I have seen an ali tube joiner get bent in the air. The model made it back safely onto the ground. I suspect a carbon fiber tube failure would be catastrophic.

Secondly it seems that your concern is with the plywood wing joiner. A solid ali one would be fine or laying one up from fibreglass with some carbon fiber tows top and bottom far extra strength would be even stronger.
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Old 04-24-2018, 11:34 AM
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Hydro Junkie,

You know.... I thought the same thing about how wood can get old and deteriorate. But then I came to the conclusion that a lot of kits are built (not just Telemasters) with the dihedral brace glued permanently into the one piece wing, and there is no catastrophic failures for the life of the plane. So, I don't see the need to go $20 on Ebay for it.... as the 7/16"ply is almost TWICE as thick. Also, I will definitely be applying 28" long struts to each side of the wing. (made from 28" x 3/8" arrow shafts) I don't fully trust leaving the area of wing beyond the 12" of joiner brace exposed to bending stresses.

Do I have your blessings? ......I never feel 100% comfortable going against suggestions, as many guys on these boards have a lot more experience then me.

J.Duncker,
I was posting this at the same time as you. You're welcome to provide your feedback about what I'm saying here in this post.

Last edited by rustyrivet; 04-24-2018 at 11:39 AM.
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Old 04-24-2018, 05:07 PM
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A Telemaster is a slow flying floater. With struts flight loads on the joint between the two halves will be low so a ply joiner 'should' do the job. If the joiner supplied had layers of different thicknesses I would look for a piece of high grade ply and cut a new one.
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Old 04-24-2018, 07:58 PM
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I think I got lost here somewhere.... The aluminum tube was to make a 2 piece wing? I agree with the majority, the tube you wish to use has a high probability of failure. A carbon tube of sufficient thickness and diameter will, in my opinion, give you a much better chance of success. Wing struts are a great idea, provided some structure is built into the wing at the attachment point, and will relieve the joiner tube of much of its loading. Now we are on to plywood wing joiners?? They work great, provided that they are glued in with a suitable laminating resin, but I don't see a plywood dihedral brace being much good in a 2 piece wing. Where did I veer off course??

Scott
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Old 04-25-2018, 09:37 AM
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Originally Posted by Pylonracr View Post
I think I got lost here somewhere.... The aluminum tube was to make a 2 piece wing? I agree with the majority, the tube you wish to use has a high probability of failure. A carbon tube of sufficient thickness and diameter will, in my opinion, give you a much better chance of success. Wing struts are a great idea, provided some structure is built into the wing at the attachment point, and will relieve the joiner tube of much of its loading. Now we are on to plywood wing joiners?? They work great, provided that they are glued in with a suitable laminating resin, but I don't see a plywood dihedral brace being much good in a 2 piece wing. Where did I veer off course??

Scott
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The ribs are too shallow to provide enough meat around a 3/4" alum tube. So instead I've decided on a 9-ply plywood joiner brace (7/16" thick x 1" instead of an alum 3/4" tube. As I had said in post #14; If the original kit intends me to glue a 5 ply 1/4" thick x 1" x 24"ply dihedral brace between the upper and lower wing spars (12" long in each wing half = 24") to hold the wing halves together forever, I don't see why I can't double that and use 7/16" thick, 9-ply removable joiner brace. If 20 year old Telemasters are still flying with a 1/4" ply brace glued into the wing, why wouldn't a 7/16" removable joiner brace work? (never mind the wing struts, which I consider besides the point) Not arguing with anybody, as much as I just want to be sure I'm thinking right before I proceed.
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(Each wing half has 46" long wing spars 1/2" wide, and I can add webbing to box them in so that my 7/16" thick 9-ply joiner brace will slip in and out of the wing halves at the field.)

Last edited by rustyrivet; 04-25-2018 at 09:39 AM.
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Old 04-25-2018, 11:52 AM
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Originally Posted by rustyrivet View Post
Hydro Junkie,

You know.... I thought the same thing about how wood can get old and deteriorate. But then I came to the conclusion that a lot of kits are built (not just Telemasters) with the dihedral brace glued permanently into the one piece wing, and there is no catastrophic failures for the life of the plane. So, I don't see the need to go $20 on Ebay for it.... as the 7/16"ply is almost TWICE as thick. Also, I will definitely be applying 28" long struts to each side of the wing. (made from 28" x 3/8" arrow shafts) I don't fully trust leaving the area of wing beyond the 12" of joiner brace exposed to bending stresses.

Do I have your blessings? ......I never feel 100% comfortable going against suggestions, as many guys on these boards have a lot more experience then me.
Okay, let me make one thing VERY CLEAR. This is your project and how you build it is up to you. That said, you don't need my blessing to build as you see fit. I gave you an alternative way of making the wing joint stronger without adding a considerable amount of weight. If you don't want to use my suggestion, that's fine by me as it's not my plane you're building, IT'S YOURS. My thought is that I want you to have a sound, good flying aircraft and I don't really care if you use my suggestions or not, just so long as you are happy with the outcome.
Happy Building
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Old 04-25-2018, 12:19 PM
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I see the light! If I understand correctly you are working on converting a one piece wing into a two piece wing with a single joiner of somesort. Now this is not as simple as it might seem.

In a one piece wing the plywood joiner is glued in place which means the load is transferred from the wing to the joiner along the length of the joiner. If you allow the joiner to float in the wing without gluing it in place the join between the wing halves will be significantly weaker and you will have a major stress point at the end of the joiner.

Also it is common practice to apply a piece of fiberglass tape to the wing join at the center. This makes the wing skin a one piece monocoque through the center. The joiner just keeps the skins apart. [ mostly ]. This is the more important factor in making the wing to wing join strong.

To convert the construction to a two piece wing you will need two joiners one can be short and small just to locate the wings. The major joiner will need to be significantly longer and stronger than the kit joiner. You will need to modify the construction of the wing to create a box for the joiner to slide into. Generally this would form part of the main spar. Balsa ribs might have lite ply doublers and care needs to be taken to extend the mainspar reinforcement beyond the end of the joiner. If your ply joiner is near the full depth of the wing then you must reinforce the box where it joins the root rib which needs to be plywood or ply reinforced. I used to wrap epoxy glass string around the box there.
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Old 04-25-2018, 01:03 PM
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I am back on track also. When I saw dihedral brace I thought a few inches into each wing panel and glue. I see that you wish to replace the wing tube with a wing blade. I have never done it, but I see no reason it will not work. You stated 12" into each wing panel, which should work. Obviously the spar box structure must be up to the task as has been stated above. My only concern would be that as the wing is built up wood and the blade is plywood is the fit. The blade must be quite snug into the wing box, since any play will be greatly amplified at the wing tip. What will humidity do to the fit? I live in the high desert where it would probably not be a problem. If you live in an area with huge seasonal humidity changes it might go from kind of sloppy to needing a hammer to take it apart.

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Old 04-25-2018, 01:41 PM
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Originally Posted by j.duncker View Post
I see the light! If I understand correctly you are working on converting a one piece wing into a two piece wing with a single joiner of somesort. Now this is not as simple as it might seem.

In a one piece wing the plywood joiner is glued in place which means the load is transferred from the wing to the joiner along the length of the joiner. If you allow the joiner to float in the wing without gluing it in place the join between the wing halves will be significantly weaker and you will have a major stress point at the end of the joiner.

Also it is common practice to apply a piece of fiberglass tape to the wing join at the center. This makes the wing skin a one piece monocoque through the center. The joiner just keeps the skins apart. [ mostly ]. This is the more important factor in making the wing to wing join strong.

To convert the construction to a two piece wing you will need two joiners one can be short and small just to locate the wings. The major joiner will need to be significantly longer and stronger than the kit joiner. You will need to modify the construction of the wing to create a box for the joiner to slide into. Generally this would form part of the main spar. Balsa ribs might have lite ply doublers and care needs to be taken to extend the mainspar reinforcement beyond the end of the joiner. If your ply joiner is near the full depth of the wing then you must reinforce the box where it joins the root rib which needs to be plywood or ply reinforced. I used to wrap epoxy glass string around the box there.

There are limits and boundaries with the cost of any job. Purchasing a single sheet of 24" X 36" plyboard online, or a 4" x36" aluminum plate ( plus additional shipping costs) to cut it into a single 1" x 36" flat stick is what I regard as prohibitive. While I do have the monetary means, the principle of spending $40 or $50 just to to make that one stick is ridiculous. There are numerous other ways to skin this cat. I'd revert back to a 3/4" x .58 walled aluminum wing tube for $16 on Ebay, and make it work, before I throw $50 into a stick.

What your input has accomplished, is for me to be reminded that I need to go about this carefully if I don't want a few months of work subject to the catastrophic failure of a folded wing. LOL Thanks for the help.
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Old 04-25-2018, 03:49 PM
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Remember you need tubes to glue into the wings as well as the ali joining tubes. These can be glass fiber or phenolic.

3/4 tube is on the small side Sig recommend 7/8 for 40 to 60 see Sig tube

For a range of tubes see wing tubes
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