Tube construction: Alternatives to conventional welding

Discussion in 'Tube and Fabric' started by Vigilant1, Mar 28, 2017.

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  1. Nov 5, 2019 #261

    stanislavz

    stanislavz

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    Just got some more info on rag - 200g/m2 is the lovest possible , real levels in time (some repainting, glue etc.. ) are close to 400-450 g/m2...
     
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  2. Nov 13, 2019 #262

    Winginitt

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    After reading all of this, my personal conclusions are these. Others may reach different conclusions.

    1. Using square tubing offers advantages in ease of cutting and matching joint intersections.

    2. Using alternative methods of joining the square tubing is much more time consuming and costly than the "conventional method".
    It requires a reasonably temp controlled area. It requires additional parts be manufactured. It requires additional material to be purchased to make the parts. It requires special rivits to be purchased. It requires a tool purchase to install rivits. It requires bonding materials to be purchased. Upon completion the adjoining members do not have metallic support over 100% of the joining points. Time needed to actually manufacture, join and cure parts is equal or greater than by conventional methods. The airplane will be heavier but not stronger. Brackets will produce unsightly buldges in fabric covering unless additional steps/parts/weight is incorporated to conceal them.

    3. Alternative methods are viable but offer no real advantage over the conventional joining method for square tubing.

    4. Alternative methods definitely don't offer any advantage when applied to round tubing as the round tubing should be coped no matter what the method of joining. Manufacturing gussets to fit properly to round tubing will be even more labor intensive than with the square tubing.

    5. If a builder feels they cannot personally assemble a fuselage using conventional means, they can tack one together and pay someone to finish it. Even a cheap HF will tack, and it requires virtually no skill. The cost of materials for alternative assembly will offset the cost of hiring someone.

    Some people just want to do something a different way because they just want to do it a different way. There doesn't have to be an advantage gained by doing it that way, they just want to do it that way......or just don't want to do something the conventional way. I understand that......I do it too.
     
  3. Nov 13, 2019 #263

    Vigilant1

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    Despite your previous statement in this very thread that you'd stop beating this drum, here you go again. Did you type this or not (bold in original)?:
    Previously, in a thread FritzW started to discuss the automated tube cutter he is designing, you inserted 2 posts and tons of graphics on your Craigslist finds (here and here). Pretty hard to see how that was germane, and the OP let you know that.

    Oh, you did it again in this thread. The OP specifically wanted to have a discussion on designing a crashworthy composite structure, but you decided you wanted to intrude repeatedly with your opinions about stall speed. Posts long enough to need a table of contents. As in other cases, the OP asked that you knock it off. You've said you'd stop doing this, but your behavior in this thread makes that seem unlikely.

    All this off-topic posting within the last 3 weeks.

    Please knock it off. Start a new thread if you want to talk about the wonders of welding.
     
    Last edited: Nov 13, 2019
  4. Nov 14, 2019 #264

    FritzW

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    When three op's have to put a stop to this guys disruptions it's time for the moderators to step in.
     
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  5. Nov 14, 2019 #265

    Topaz

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    Moderator Note: I deleted the last problematic post as completely off-topic. You won't have a problem in this thread anymore. Clearly we missed this one, and for that I apologize. If this particular problem keeps happening elsewhere, please report it immediately.
     
    Last edited: Nov 14, 2019
  6. Nov 14, 2019 #266

    cheapracer

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    I ignored him a long time ago, recently I'm finding it the best solution.

    Some might think it's beneath you to do it, and that you can handle them, nah, it's just easier, really cleans the threads up as you browse through them.
     
  7. Nov 14, 2019 #267

    Topaz

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    The "ignore" list is certainly helpful if you're not getting along with someone, but please report consistent trolling to the moderators. We can't be everywhere, and member reports brought mod attention to this case.
     
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  8. Nov 16, 2019 #268

    proppastie

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    I see much design with body-bound press fit fasteners or tapered pin joints ....mainly in wing attach fittings and wing carry through fittings or spar caps....What might be the reasons for that considering your statements......So should I not be concerned if I have a slip-fit wing attach bolt connections vs press-fit wing attach bolts?

    and weather this should be a separate thread or not....I do not know,...found these posts here so I kept it here.
     
  9. Nov 16, 2019 #269

    rv7charlie

    rv7charlie

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    I, too, am quite confused by the 'friction does all the holding' arguments. The 'friction area' on an RV-7/8 wing is around 4 sq in each, on the top & bottom spar caps, and secured by 2 AN6 & 2 AN4 bolts on each cap. And Van's goes to the trouble and expense of using 'close tolerance' bolts that must be driven into place. What's the point, if 8 sq in of friction does all the work? Why do props have 3-6 big fat lugs that are a close tolerance fit into the back of the prop hub, when a single centering cone in the middle would work fine to center the prop?

    Here are a couple of things to try, to test the friction idea. Cut a couple of 12" long, 1" wide straps of your favorite aluminum, match drill a hole about 1" from one end, and rivet properly with a driven -3 rivet. Now see how much force it takes to rotate the strips around the rivet. Next, replace the tapered nose lug nuts on your car with flat-faced nuts. You can swap one at a time, to keep the wheel centered on the hub. Now, drive it for a week, and report back on your results.

    Charlie
     
  10. Nov 17, 2019 #270

    FritzW

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    You can't say ALL joints are slip critical (rely on friction) or ALL joints are bearing type (rely on fastener shear) it depends on how the joint was designed. ...some are, some aren't.

    I even found one source that suggests slip critical joints aren't usually used in aluminum.

    "Aluminum connections also may be bolted or riveted. Bolted connections are bearing type. Slip-critical connections, which depend on the frictional resistance of joined parts created by bolt tension, are not usually employed because of the relatively low friction and the potential relaxation of the bolt tension over time"
     
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  11. Nov 17, 2019 #271

    Hot Wings

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    I try to stay away from bolted joints, even in steel, that are dependent on the friction. If the design checks out as critical with only shear I might use 30% of the friction from the clamping loads to see if it then has the needed FOS.
    Yes, designing with the friction taken into consideration means that we can build a lighter joint, but in the real world the clamping force of a bolted joint, and hence the friction component, varies a lot - even if the bolt is torqued to specs. There are just too many variables with a bolted joint that can't be controlled well enough in the field. That is why we see torque-n-turn and torque to yield specs.

    At least with a riveted aluminum structure using aluminum rivets the change in clamping pressure with temperature change is minor. Probably is for a bolted thin aluminum structure as well? At some point with a thick aluminum part using a steel bolt the change in clamping pressure due to temperature change becomes significant. When this happens then the shear and bearing load limits establish the FOS.
     
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  12. Nov 17, 2019 #272

    rv7charlie

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    I neglected the most obvious real world example of 'friction' not telling the real story. Anyone who's used an IVO Prop on a direct drive engine, especially a Lyc, knows it "ain't so". IVOs don't have drive lugs. And if installed on a Lyc, the blades are guaranteed to move. They started with copper 'witness tape' between the blades, and after everyone using the prop direct drive was breaking tape, they switched to stainless steel tape. Everyone still broke the tape. Finally,bBefore IVO quit selling them for Lycs, they even tried knurling the hub plates to 'bite' into the faces of the blades. All that accomplished was chewing up the faces of the blades. I have personal experience with this. Now I realize that proper installation is a factor. You can trust that I knew what I was doing, or not. But if no one who tried using one on a direct drive 4 cyl Lyc could get it to work, to the point that IVO quit selling them for Lycs, that's pretty telling...
     
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  13. Nov 17, 2019 #273

    wsimpso1

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    Please please please don't do this. This gives a very real chance of wrecking your wheels and makes possible losing a wheel while driving.

    The cone lug nuts are there for a couple important reasons:

    To center the wheel - yeah, the hub has a protrusion that centers in a bore on the wheel that centers the wheel - centering is important to balance of the wheel as installed and rotating on the bearings;
    To roughly double the friction keeping the nuts from loosening as you drive;
    To provide consistency in clamping the wheel to the hub.

    Seriously, do not investigate this with your cars lug nuts. There have been cars crashed and lawsuits over mismachined hubs that gave contact at smaller radii, with a lot of vibration occurring in the car prior to lugs or wheels failung and then wheels flying away from the car...

    I shall respond on friction elsewhere...

    Billski
     
  14. Nov 17, 2019 #274

    proppastie

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    how do you define "critical" .....perhaps as regards to Ultimate or Ultimate + FOS?
     
  15. Nov 17, 2019 #275

    rv7charlie

    rv7charlie

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    I guess I should have searched for a tongue-in-cheek emoticon. :) I'd hope no one would actually try the lug nut trick. I know that friction can work in some applications (ex: the R8 taper on a Bridgeport mill spindle), but I've always heard that it's ignored when designing a/c structure. I *know* it doesn't work with prop mounting.
    I read about a controlled experiment years ago where otherwise identical multi-rivet joints were created using both universal head (flat sheet) and dimpled sheet with 'countersunk' style rivets. The test assemblies were pulled to fail them in shear, and the dimpled joints were significantly stronger than the undimpled joints. To my untrained eye, in both cases the friction in the joint has to fail long before the rivets fail in shear. Am I looking at it wrong?

    Charlie
     
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  16. Nov 17, 2019 #276

    Hot Wings

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    In my case a poor choice of words. "Critical" being under the design point , either yield or ultimate, by 15% or so. In other words close enough to give me a 'warm fuzzy feeling' that using the 30% of the friction from clamping load provides the desired FOS.


    Side note on lug nuts.........
    It has always surprised me that we didn't follow the lead of left handed threads on one side all cars. I've had an aluminum front wheel depart my Dodge truck 2 days after new tires. I watched the guy use a torque wrench - after showing me the setting. Distance between the first rumble and brake rotor on the pavement was under 300 feet. If it had been a 60's or older Dodge I wouldn't have a story to tell.
     
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  17. Nov 17, 2019 #277

    proppastie

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    95 Toyota/Lexas has flat lug with pilot,....problem with old LH thread Dodge was not knowing what the L on the lug met....

    My case currently have semi-slip fit bolts on wing carry through....some tighter than others. See build-log later today.
     
  18. Nov 17, 2019 #278

    BJC

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  19. Nov 17, 2019 #279

    FritzW

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    Last edited: Nov 17, 2019
  20. Nov 17, 2019 #280

    BBerson

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    Prop bolts need to be retorqued periodically for a wood prop, otherwise the prop will move and the friction will char the face and then it gets looser and fails. My flying buddy had the flywheel bolts shear on his Jabiru. While he was installing new flywheel bolts I picked up his wood prop and showed him his charred prop face. He did not know about the need to retorque wood props (50 hrs or something) The loose prop had broke his flywheel bolts, fortunately while taxiing.
     

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