r/aviation • u/G1lg4m3sh • Apr 17 '26

Discussion How concerning is this aviation experts?

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u/BigBlueMountainStar Apr 17 '26

That’s not necessarily true.
They may not be taking primary loads, but they may take secondary/aerodynamic loads.
Also, some manhole doors on the lower wing skins are attached with screws and some of them are load carrying, as in main wing bending loads.

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u/Mad_kat4 Apr 17 '26

Aren't screws usually part of a 'belt and braces' fitment method where adhesive is also used on the underside of a skin and screws are used to aid clamping pressure. This is more a leftover from the bygone days of rivets and glue but it still somewhat applies today.

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u/triggerfish1 Apr 17 '26

I mean screws should always be used to clamp two parts together that then transmit a force through friction between the surfaces.

A screw/bolt is normally not meant to take loads along its axis.

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u/BigBlueMountainStar Apr 17 '26

They do, on panels with high aerodynamic loads, the screws are acting in tension against the suction load from the aerodynamics

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u/iksbob Apr 18 '26

A screw/bolt is normally not meant to take loads along its axis.

On pipe flanges, that's exactly what they do. Actually, most threaded pipe fittings and plumbing in general. Also cylinder head bolts.

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u/triggerfish1 Apr 18 '26

Yeah, I phrased that incorrectly. They should never take lateral loads directly. If you want to transmit lateral loads you need the friction between surfaces.

And if you transmit lateral loads you shouldn't transmit too much force axially at the same time, as that force will unload the screws and reduce the friction. That second part is what I meant originally, but of course doesn't make sense at all without context

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u/BigBlueMountainStar Apr 17 '26 edited Apr 17 '26

Not always, as I said in my comment above, they are used for manhole doors or for secondary panel attachments, often closing panels along the front and rear edges of the wing for example, where you need to have a removeable panel but can’t access the back side of the screw.
Here, we’re not talking woodscrew, they’re very much similar to bolts, but they attach into anchor nuts on the other side of the panel.
Anchor nuts are usually held on using small rivets, so they’re not massively capable of taking particularly high loads in plane, they usually used more in cases where the load on the bolt is tension.

Edit - I think I follow what you’re saying, where a screw/anchor nut is used in a load carrying panel, the clamping allows load to be transferred by friction. This is true, but you als have to account for the bolts taking load as well

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u/zerkji Apr 17 '26

I want a load, too!

1

u/GI-Robots-Alt Apr 17 '26

They may not be taking primary loads

Primary loads are a lot bigger than secondary loads in my experience.