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Wing rib spacing

Old 01-15-2004, 11:38 PM
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Patriot
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Default Wing rib spacing

Ok, this one is starting to bug me. I blew up a set of plans to make myself an 80" bipe. The original shows the ribs about 3" apart, and the blow up shows the ribs about 5" apart. I figured I would just add a few more ribs to make up for the differance. Problem solved.
Then I started looking at real photos of a full scale version of this bipe and it shows the same number of ribs as the original plans. So what I am asking is, is it ok to space the ribs 5" apart to keep it scale to the real thing?
And for a wing this length, would it be ok to use 3/32", or go up to 1/8" balsa for the ribs?
I am planning on adding shear webbing throughout and some carbon fiber laminate over the wing sheeting to reinforce.

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Old 01-16-2004, 12:21 AM
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Default RE: Wing rib spacing

1/8 for sure. That's a terribly wide spacing.

Assuming a scale up from your 80 inch span (roughly 7 feet) to a 21 foot span (scale for a bipe) that would make the rib spacing 15 inches. About right for the much tougher cloth covering the full sized stuff uses. So your 5 inch spacing would be OK but plan on 1/8 ribs and then using one of the fabric based coverings for a bit more strength and stiffness to the model's covering.
Old 01-16-2004, 02:50 AM
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Default RE: Wing rib spacing

Yes I am going with Koverall. Strong stuff. I think 1/8" is going to be the way to go as well. 3/32" with such wide open bays seems a bit flimsy. Thanks.

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Old 01-16-2004, 11:51 AM
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Default RE: Wing rib spacing

Hold on, is this wing sheeted or open bay? Comments seem to point both ways here. I am of the opinion that ribs are generally one thing any particular plane can use less of. Open bay you need 'em to keep the covering from sagging. So, just space 'em so the covering looks good. Sheeted you need them to keep the skin from buckling. In general, skin buckling is not going to be the problem at this spacing, especially if you are adding shear webs and other happy stuff. They really don't do anything else besides giving the wing its shape.

I once worked on a full scale 2 seat aluminum GA airplane that had a root rib, a tip rib, one full rib outboard of the landing gear and another half-rib partway out. That's 3.5 ribs per side. Other than that, there were just skin stiffeners.
Old 01-16-2004, 12:03 PM
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Default RE: Wing rib spacing

Ok, ok, I will clarify. It is basic wing construction seen everywhere.

The first 1/3 of the wing from the leading edge back is sheeted. The aft 2/3 is open bay with trailing edge stock in the rear. A good majorit of kits I have built have all been designed like this, so this is no great departure from what I am used to. I am jus a little concerned with the 5" between ribs vs 3-31/2" I am used to. I want to keep this 5" spacing to keep the scale look of the plane.
So, as a result, I think I will be going to 1/8" thick ribs, ,and sheer webbing along the whole length of the wing with laminate carbon fiber to reinforce the whole kitt'n kaboodle.

Patriot

Wait 'til you guys see what I am building, will post pics here when ready. Still in design phase and wood acquisition phase. LOL But I am getting there.
Old 01-16-2004, 12:13 PM
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Default RE: Wing rib spacing

OK, the wing strength will be handled by the sheeted leading edge. You don't need to go to the thicker ribs. Also, you don't need to add shear webbing more than halfway out along the span. The ribs are fine for support out toward the tips. Did you know that the Cessna 172 does not have any shear web for the last couple feet of wing at the tip? Just don't need it.
Old 02-07-2004, 11:59 AM
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Default RE: Wing rib spacing

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