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Hi all 

Can anyone please point me in the right direction , I want to know how to go about building a wing when the bottom of the ribs are not flat .if any one can suggest a build that would be worth looking at or a brief discription i would be most grateful 

many thanks in advance 

 

Tony J 

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Tony,

 

Some plans show tabs added to the lower rear of the ribs to align the ribs during the build, which are cut off after the wing has gained some stiffness - usually when the upper surface is fully sheeted.

An alternative is to pin or prop the rear of the ribs on a suitable piece of strip wood of the correct size, this is much easier with a fixed chord non tapered wing profile.

Another way is by using a series of cradles to fit to 3-4 ribs along the span. This holds the wing in alignment until the wing is stiffened.

 

What are you thinking of building?

A kit or plan will normally have some suggestions as to how the designer intends the wing to be built.

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Another method I've seen is to accurately bore two small holes of the same distance apart in each rib (doesn't matter if the wing is tapered as long as the holes are all in line) then suspend the ribs with two stiff tubes fastened to blocks at each end, then add LE, TE, spars, etc until the assembly is stiff enough to remove from the jig.

 

But most modern plans seem to opt for the tabs method - if the ribs are laser-cut then so much the easier!

 

Edited by Jonathan M
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I use a piece of strip wood near the TE. Works for me.

 

If you mark the centreline on each rib you can use that to help line things up. 

 

Generally speaking any method is simple on a constant cord wing. It's with tapered wings that you need to be extra careful not to jig in an undesired warp. 

 

Edited by Nigel R
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I've added an album to my profile called "S6b_construction", which shows the method I used for sheeting the wings of my S6b with a double set of jigs that conform to the shape of the ribs. I think pictures speak loader than words. The underside was sheeted first, so the first set of jigs (beneath every third rib) conform to the shape of the upper side of the wing without the sheeting. The jigging pieces, made of 1/4" balsa are glued straight to the glass building "board". The upperside was sheeted next with the wing supported by jigs that conform to the lower side of the wing plus sheeting. A combination of CA and aliphatic resin (mainly the latter) was used to glue the sheeting. The sheeting was held in place while the glue dried with weights (model magazines); and leading edge sheeting by a liberal use of masking tape. (The pictures show what I mean by liberal!) Note there is not a pin in sight. The benefit of this method is that the wings come out absolutely true. The sheeting cannot create warps: indeed, it locks the wing into the correct shape.

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John, re. S6b_construction,

I understand building the wing on the jig but am puzzling over how you cut the sheeting to size? The sheeting appears to extend all the way to the leading, trailing edges and wing tips. Do you make a flat template for cutting out sheet that will be curved when glued to the wing? Is it an iterative process of offering up sheet to the ribs and trimming it to fit?

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I’ve done this by making support blocks from 1/8” balsa to pin under the (false) leading edge and trailing edge of the wing every few inches during construction (see photo). This method has worked well for me on a number of occasions.
 

large.ED4DCEBF-7D1C-4C24-B761-D5D5AF38A925.jpeg.f23d4524eb1e13b81f407c755a8eda13.jpeg

 

Edited by EvilC57
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