Rib lengths (again)

[Frank]

Having looked at various discussions here regarding rib lengths, I am tending toward trimming the ribs to length upon assembly. That means leaving them all at full length for now. But what is "full length"? The plans indicate the ribs sit TIGHT against the spar/capstrip/spacer material. Is that how it works out in reality? Or is there a slight gap in there? Since the rib attach angle is holding the two structures together, I'd think you might want a small gap as long as rivet spacing is not harmed.

Also, for measuring rib lengths, where are you measuring from? For the nose rib, from the nose at the centerline? For the center rib, can you find a point along the centerline to measure from, forward and back?

[geraldmorrissey]

I based everything on the spar web C/L's. They are convenient datums. Good decision to "trim on assembly".
Gerry
Patrol #30

[johnb]

Frank, on mine, I set it up with a small gap between the rib and the spar, making sure I maintained edge margin in both the rib and attach angle.

I measured everything off of the spar reference planes. When I made my mdf master template from the mylar, I marked the spar planes on the template. I used the master template when I made my router templates, and measured from the spar reference plane to mark where to trim the router templates.

Hope this helps.

[Frank]

Thanks Gerry and John. Yes that helps. All of the lines are transferred onto my master and working templates. For some reason I was thinking I needed a second reference besides the spar centerlines.

I guess its not so much the length of the rib as it is the amount being trimmed: that's the dimension to be concerned about.

That, and getting everything aligned in the assembly jig.

Much obliged!

[geraldmorrissey]

Replicating the mylar curve with your structure is what you should be concerned about. Trim and position the detail parts to achieve that end. Somtimes a 10,000' view helps.
Gerry
Patrol #30

[geraldmorrissey]

I would build in some gap between edges and surfaces to eliminate fretting. Maintain required fastener edge distance but not too much. It's extra weight.
Gerry
Patrol #30

[Frank]

That's what I was thinking. Fretting. Just looked it up. That's why we trim the nose off the nose ribs after the skin is fitted, yes? Good point about the curve and the contour and the 10000'.

I read somewhere here that the full-length tip ribs will determine a lot, when it comes to assembly and alignment.