This how airbus wings attach to fuselage

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Toobuilder

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...Bolts and rivets mostly work by establishing clamp loads between the joined members. The joint has security only as long as the friction is larger than the active loads and the tensile loads do not open the joint. If active loads exceed friction or the joint opens and closes, the joint works and fatigue develops in the joined members and in the fastener. In the end, we need joints to be clamped securely against motion...

Billski
This is not universally applied in aerospace. My last "big" company took no consideration for clamp friction in shear joints. Each fastener was analyzed as an individual pin joint.
 

Mad MAC

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We wont mention the airliner tear downs were the fuse skin rivet shanks are all hour glass shaped from moving, every time there was a pressisation or the airliners dipping paint stripper from skin joints 4 years after being repaints.

For aircraft joint friction only applies at low loadings, not ulimate and unlikely at limit.
 

Aviator168

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wsimpso1

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This is not universally applied in aerospace. My last "big" company took no consideration for clamp friction in shear joints. Each fastener was analyzed as an individual pin joint.
Oh, I do not doubt that joints are analyzed and sized as a pinned joints. Shigley covers all six (IIRC) failure modes and implies all should be checked, but then goes into detail showing how to check joint friction and stability. Sizing so the pinned joint is safe is the conservative way to do it. That way if preload is not established or lost, the joint will not immediately fail, the joint will "smoke" or crack paint and torque seal, and otherwise indicate it is getting loose and can be caught on next inspection, then dealt with.

A joint sized as a pinned joint will generally have excess clamp load if decently set (rivets) or torqued (bolts) and will then not work in use. Chosing the number, size, and pattern of fasteners using pin assumptions is thus more tolerant of the factory and the field, and thus safer in use because it gives lots of time to catch it. That is good conservative engineering in the first sense, failure mode reduction, and covers FMEA all at the same time. Incorporation as a good design practice likely occurred long before FMEA was invented.

Pinned joints without significant clamp loads and using things like shear bolts are still used some places. This Scarebus wing does not appear to be one of them.

None of the above discussion means that clamp load is not what is actually holding the joints fixed against operating loads... As I said above " bolts and rivets mostly work by establishing clamp loads".

The skeptical and curious among us are free to analyze a joint using only pinned joints at say 1/4 of yield stresses and see just how much relative movement occurs through elastic deflection of the pin and hole even when assembled with zero clearance. Usually way more movement than the system should see.

Billski
 
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BBerson

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I don't know what a drive fit is, but I've done a lot of structural work on 727's and 737's, and there was lots of original Hi-Loks, also Huck bolts. Maybe that is what your friend is referring to.
Might be Huck bolts, he didn't say. Huck LockBolt, Huck fastening Tool, Huck Fasteners, Huck Pin, Huck Collar
He said AN bolt are close enough tolerance for my ultralight, if I grind a slight taper on the reamer in the lathe. And drill 1/32" smaller than reamer.
 

Angusnofangus

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According to this definition, drive fit is interference fit.

I know what 'interference fit' refers to and it doesn't take much to figure that 'drive fit' could be the same way to say it. But BBerson's friend referred to 'a drive fit'. Obviously an interference fastener, but which one, I don't know as sometimes Huck bolts and Hi-Loks are installed in transition fit holes.
 

TFF

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I don’t think huck bolts are removable. I think the final tightening deforms the threads to lock. Hi locks have the Allen on the shank. You have to have a tightening tool with a hole in it so you can fish the Allen through. Socket wrench with a hole in the center or a socket with outside flats. Hi locks are definitely cheaper to tool up for.
 

Angusnofangus

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I don’t think huck bolts are removable. I think the final tightening deforms the threads to lock. Hi locks have the Allen on the shank. You have to have a tightening tool with a hole in it so you can fish the Allen through. Socket wrench with a hole in the center or a socket with outside flats. Hi locks are definitely cheaper to tool up for.
Huck bolts are definetely removable, There are no threads, but there are ridges on one end that the collars are swaged around. There are collar cutters made for removing them, or just use a hammer and chisel.The collar cutters also work on aluminum Hi-Lok collars.
And you are spot-on about Hi-Loks not needing any special tooling, whereas Hucks do.
 

PTAirco

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Oh, I do not doubt that joints are analyzed and sized as a pinned joints. Shigley covers all six (IIRC) failure modes and implies all should be checked, but then goes into detail showing how to check joint friction and stability. Sizing so the pinned joint is safe is the conservative way to do it. That way if preload is not established or lost, the joint will not immediately fail, the joint will "smoke" or crack paint and torque seal, and otherwise indicate it is getting loose and can be caught on next inspection, then dealt with.

A joint sized as a pinned joint will generally have excess clamp load if decently set (rivets) or torqued (bolts) and will then not work in use. Chosing the number, size, and pattern of fasteners using pin assumptions is thus more tolerant of the factory and the field, and thus safer in use because it gives lots of time to catch it. That is good conservative engineering in the first sense, failure mode reduction, and covers FMEA all at the same time. Incorporation as a good design practice likely occurred long before FMEA was invented.

Pinned joints without significant clamp loads and using things like shear bolts are still used some places. This Scarebus wing does not appear to be one of them.

None of the above discussion means that clamp load is not what is actually holding the joints fixed against operating loads... As I said above " bolts and rivets mostly work by establishing clamp loads".

The skeptical and curious among us are free to analyze a joint using only pinned joints at say 1/4 of yield stresses and see just how much relative movement occurs through elastic deflection of the pin and hole even when assembled with zero clearance. Usually way more movement than the system should see.

Billski

Most light aircraft though don't seem to rely on any clamping force. Look at a typical strut or wing root attachment on a Cub or Aeronca. If you tried to apply any clamping force you'd mash the fittings. Also with the normal deflection of spars under load, if the root bolts on a strut braced wing were clamped tightly to the fuselage allowing no rotation, it would do horrible things to end of a wooden spar, no? The straps attached to the outer wing strut fittings certainly would add some clamping force, but against a wooden spar you'd be careful to only apply a minimum. I would say in light aircraft, deliberate clamping y bolts is the exception, rather than the rule. Which is the exact opposite in the automobile manufacturing world.
 

Dan Thomas

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Most light aircraft though don't seem to rely on any clamping force. Look at a typical strut or wing root attachment on a Cub or Aeronca. If you tried to apply any clamping force you'd mash the fittings. Also with the normal deflection of spars under load, if the root bolts on a strut braced wing were clamped tightly to the fuselage allowing no rotation, it would do horrible things to end of a wooden spar, no? The straps attached to the outer wing strut fittings certainly would add some clamping force, but against a wooden spar you'd be careful to only apply a minimum. I would say in light aircraft, deliberate clamping y bolts is the exception, rather than the rule. Which is the exact opposite in the automobile manufacturing world.
Service manuals for various aircraft will specify bolt/nut torques for such locations, and if they don't the standard-practice torques apply. There is some clamping force involved, as we don't want the joint shifting and wearing the hole bores or the bolts.

Wooden spars don't get the strut or root bolts directly in them. There are fittings with multiple bolt holes that fit closely to the spar, with carefully-drilled holes through the spar so that bolt fits are very close. Clamping loads are spread out over the faces of that fitting. Sometimes there are bushings in larger holes in the wood to spread the loads over a larger radius and to prevent crushing the wood with bolt torquing.

The larger single strut and root bolts go through tabs on the fitting and the lugs on the fuselage and take more torque.

Taylorcraft had the bushings:

1615600285631.png
1615600325544.png

1615600351679.png

Old (small) and new (large) bushings.

From Wing structural work

Note the plywood doublers on the spar root.
 

BBerson

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Aeronca has large spar bushings also. About 1", I think. (45 years since I made a set of spars)
 
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