Spar spacing

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Re: Spar spacing

Postby edgeau » Wed Apr 26, 2017 4:36 pm

Actually, after some similar advice elsewhere, I am in the process of making some curved pieces to go between the spars to get a torsion box effect.

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Re: Spar spacing

Postby Andrew Herrick » Wed Apr 26, 2017 5:08 pm

edgeau wrote:Actually, after some similar advice elsewhere, I am in the process of making some curved pieces to go between the spars to get a torsion box effect.

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If you're making a conventional roof - interior plywood ceiling, roof spars with foam, then exterior plywood sheathing, then outer skin - it's hard to imagine getting any real-world advantages from adding curved blocking members. A torsion box is useful because it creates a flat, THIN surface that resists longitudinal warping. Your roof isn't flat. It's curved - hugely so. And unlike a true torsion box, your roof is "bounded" on four sides by the walls and floor. It can't really twist along its centerline by virtue of its geometry and boundaries, and once the skins are installed, it can't rack much, either.

Not trying to insult your intelligence. Just that I can't imagine all the hours it will take to manufacture curved blocking members that fit precisely between the roof rafters, and unless I'm way off in my analysis, I'd rather save you the hassle :)

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Re: Spar spacing

Postby dales133 » Wed Apr 26, 2017 5:48 pm

If anything id just glue and screw some triangular blocks at the back of the hatch/ spar area

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Re: Spar spacing

Postby edgeau » Wed Apr 26, 2017 10:25 pm

No offense taken. This is a learning experience for me. I might know what I am doing by the time I finish. In fact I am enjoying the process as much as I do camping so I can see myself doing another one.

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Re: Spar spacing

Postby KCStudly » Thu Apr 27, 2017 6:19 am

The skin becomes the diagonal shear member. Essential the skin is the diagonal brace. This is why it is so important to build the hatch in position.
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Re: Spar spacing

Postby edgeau » Sat Apr 29, 2017 5:46 am

It turns out I needed to put the centre line in for a completely unexpected reason anyway. When I went to buy my roofing ply they could only supply sheets that bend on the long axis so I am going to have a join run along that centre line.

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Re: Spar spacing

Postby Andrew Herrick » Sat Apr 29, 2017 10:46 pm

What sort of plywood are you using, Edge?
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Re: Spar spacing

Postby dales133 » Sun Apr 30, 2017 1:24 am

edgeau wrote:It turns out I needed to put the centre line in for a completely unexpected reason anyway. When I went to buy my roofing ply they could only supply sheets that bend on the long axis so I am going to have a join run along that centre line.

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Hard to get anything else in aus mate.
I ended up just cutting 2400 sheets to the width and joining 3 from front to back

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Re: Spar spacing

Postby edgeau » Sun Apr 30, 2017 5:25 am

Andrew I am using 6mm marine ply for the roof.

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