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Aluminum Square Tube Gussets - what's the best fixing?

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Jonny C

Member
Joined
Jun 17, 2014
Messages
17
Location
London, UK
I’m designing a single seat airplane (that’s ended up quite similar to the Bede BD6). The fuselage is a basically a warren truss made from structural square 6082T6 tube (similar to 6061T6) with a non-structural composite fuselage shell that’s removable for inspection.

I’ve built a Zenair 601 and I studied aeronautical engineering at university so the calculations and building are no problem – but the fixings used in the gussets of the fuselage truss are one area where I’d like to hear your suggestions. Some possibilities:

1. Bolts full width through the gussets and tube – but I’d prefer an interference fit fixing to avoid fretting and a through bolt would result in a bending moment in the bolt. And weight would be pretty high.
2. A close tolerance bushing through the tube + clevis bolt
3. Blind rivets like CherryMAX (but even in perfectly reamed hole these aren’t totally vibration resistant)
4. Blind bolts in each side of the gusset – something like a Cherry Maxibolt or Visu-lok – but these don’t really have an expanding shank so I’m not sure about using them in the primary structure
5. Monogram’s Radial-lok which is an interference fit vibration resistant blind fastener – my preferred option… but I don’t know if I can get hold of them http://www.monogramaerospace.com/products/blind_bolts/radial-lok

The joints with the greatest axial forces (around the wing spar / landing gear) are the ones where I really want the best fasteners – maybe the much lower forces in the empennage will mean I could use locked spindle structural blind rivets there.

So, aiming for the highest quality joints, I’d be very grateful for any suggestions on the fixings.

Additionally, would you assemble the truss members touching one another at the joints, or maintain a tiny gap to avoid fretting?

I’ll share the designs here once the details are all finalized.

Thanks


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