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Old 05-12-2013, 05:52 PM   #1
bamaerker
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Default Can these spar webs be salvaged

I bought a Sig 4 star 20 kit a few months a go, the time has come to start on it, but now the spar webs are pretty warped. Can I use them, maybe build the wings pinned down real well and spray them with windex, or just have sig send new webs.


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Old 05-12-2013, 07:07 PM   #2
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don't use them. call Sig and ask for replacements,they're good people and I've talked to them when doing mods and they were helpful.

you could also cut yourself two new pc's scratch,just go to the local hobby art store and p/u the wood.[thats what i would do. then you can also replace any other warped wood....those pc's are as bad as I've seen come from a kit,was this new from Sig or was it bought from someones old stock.

narrow is the place to land...wide is the space to crash....choose the narrow way!
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Old 05-12-2013, 07:33 PM   #3
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I agree with Stuart, those pieces would make it hard to build a good straight wing panels, and that is vitally important.

If those are the webbing between the spars, it seems that Sig is using them as a spacing guide for the ribs.

Every kit I have built (over 25) that uses spar webbing runs the grain vertical to better handle the stress between the spars.
Proper shear webbing allows the spars/webbing unit to act like a MUCH bigger piece of wood. Exactly like a TJI floor joist works in a good home. Otherwise you just have 2 stiff sticks of wood, that bend with load. Proper gluing of the webbing to the spars is VERY important.

On an aerobatic design like the 4 Star, I would recommend getting the new pieces from Sig, and also backing them up with vertical grain 1/16 balsa cut to fit between the ribs but a good fit to each spar.

It's nice to see someone building a kit, instead of just buying an ARF.

Dave R, Proud PGR rider.
When you have flying skills like mine,
You become a master at repair.
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Old 05-12-2013, 07:56 PM   #4
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Default Thanks

Thanks for the replies, kinda confirmed what I thought. I'll call sig tomorrow and get new ones on thye way. I like the building because it doesn't look like all the others and it is just fun to do.
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Old 05-12-2013, 10:02 PM   #5
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Those main spars could easily be salvaged. Midwest flat CF sparring makes for a strong wing main spar, when laminated to the main spar. I use the light .019"x .118" flat spar, although there are heavier/stronger sizes. For a clean installation, the balsa spar can first be notched to fit the CF spar. The CF spar will then be flush with the main spar, after it is glued into the recessed notch. This works well, as the wing airfoil formers can be installed over the notched main spar, without having to notch them to fit over the CF lamination.

Ideally a CF spar would be laminated along the top and bottom of the main spar, but even with a single CF spar laminated at the center (neutral axis) or the main spar, it will still add strength, as well as straighten the bent wood main spar.


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Old 05-13-2013, 12:02 AM   #6
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I don't know but even using carbon fiber I think I would just cut them out again by hand. The look simple enough and could save you some time.

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Old 05-13-2013, 11:07 PM   #7
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Originally Posted by starcad View Post
I don't know but even using carbon fiber I think I would just cut them out again by hand. The look simple enough and could save you some time.
Along those lines, they could be re-cut using thicker stock, then notching the airfoil formers to match the added thickness. I've cut more of those by hand that I can count, often for old designs like the photo posted previously that used a different wing design, where the parts had to be drawn using the former heights. With the parts on hand, it would be easy to cut new main spars. They could also be re-cut to include cap spars in the design, reinforcing the weak point of tab-and-slot wing spar/former design. A sheeted LE would obviously reduce the need for that type of reinforcement.
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Old 05-14-2013, 01:06 AM   #8
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Default New spar webs on the way

Called Sig and they should be shipping out some new webs, hopefully thyey wont take to long to get here. Thanks for everyones words of wisdom.
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Old 05-17-2013, 02:26 PM   #9
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What happened to old skills ?

Warped / bent pieces were damped, clamped and brought back to use ...

Additional small gusset pieces can be used - even in foam to straighten up items.

A spar like this would be just a challenge to overcome in my den ! I don't have luxury of such replacement parts in post where I live !

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Old 05-17-2013, 03:28 PM   #10
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Originally Posted by solentlife View Post
What happened to old skills ?

Warped / bent pieces were damped, clamped and brought back to use ...

Additional small gusset pieces can be used - even in foam to straighten up items.

A spar like this would be just a challenge to overcome in my den ! I don't have luxury of such replacement parts in post where I live !

Nigel
Most kits i bought the company is now out of buissness so i cut all replasement parts also. It only takes 30 miniutes or so but i bet most times its straighter than the company would send out if they could or would . joe
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