Have you encountered this?

[Frank]

The long 1/8 X 1 inch material for cap strips is bowed.
Likely a result of manufacturing.
I can clamp in the middle and easily bring the ends into line.
But it does then store that tension/stress in the structure.
Pictured is the worst two pieces.

[geraldmorrissey]

I would make spacer bars out of those.

[Frank]

The LSA main spar spacer bars are 1/2 inch and I have all that material.
The long bowed 1 inch pieces for cap strips can easily be clamped in position.
But there will be some amount of stress induced into the structure.
So I'm wondering if that is a concern or not.

[rodsmith]

I wouldn't think so, but I'm not a structural or aeronautical engineer. I'd suggest giving Bob a call. Always learn something when I talk to him.

[geraldmorrissey]

I had some of that on my rear spar caps but was able to clamp the caps straight. But they were only 1/16" thick. Can you use these parts for your shorter caps? It looks like the curve is greater on one end then the other. If you can easily clamp these parts into position I would not worry. Put the curved caps in so the curves are opposite to one another so you don't build a curve in the finished spar. But if you have to put considerable force into straightening these parts, I would scrap them. If they are wider then the dwg callout file some material off both edges, this will help some. I have some clamps that will make life easier for you. If you want to borrow them, PM me. They will insure the capstrips are tight against the spacer bars and the capstrips are straight. They were made for a Patrol spar but have enough adjustment that they should work for your plane. Working with curved capstrips is a royal PITA. It can be overcome but will cost you many hours futzing around trying to get everything straight.
Gerry
Patrol#30

[Frank]

Many thanks for the info and your kind offer, Gerry. Let me think about this.
Currently my plan for the order of operations would be something like this:
Cut (and flange where indicated) the lightening holes.
Then drill the cap strips/web (confirm their straightness by string line).
Then size and cut the spacer bars (I've read of the importance of positive contact with the cap strips).
Then drill the spacer bars/attach angles/web.

Yes having to deal with bowed bar stock looks to be a pain. Good tip to have the bows oppose each other.

Those builders who cut their cap strips from sheets of material won't have to deal with this. They'll have a different set of headaches.

[geraldmorrissey]

Consider cutting all the spacer bars, splice plates and root fittings on a mill. Having all the "verticals" very close to the same width, with nice crisp 90 degree edges makes assembly easier. Locate the root fittings and splice plates first. Add bowed capstrips and spacer bars. Add many clamps, futz and swear. Measure and remeasure. A long straight edge is useful. I used 4 strings for alignment, they must be TIGHT. Pad the clamp feet so they don't mar the AL. Custome fitting spacer bars is tedius, each one will be different. When it comes time to break it down and prime, getting all those unique parts to go back together in the right orientation is exciting. You need a good system of identification no matter how you fab the parts. With a machined part, repairs are easier.
Good Luck
Gerry
Patrol #30

[alaskabearhawk]

I didn't build my wings so I don't have any great words of advice in this particular area. BUT, I do know that any time a part or piece is forced into place just means I wound up a spring and fastened it in place. The stress isn't going to magically go away. If it were me, I would use them somewhere else if possible and get a new set that is straight.

You could try to straighten them, but you would have to make a tool to keep the chord straight. I made this tool to put a curve in my stringers: http://www.mykitlog.com/users/displa...217910&row=129

I suppose you could do the same in reverse and slowly coax the cap strip material straight.

Just my .02 cents...

[marcusofcotton]

Did you talk to the supplier about it?

I recall some time ago some folks cutting their own strips and had a curve until dressing the edges.

[Sir Newton]

I cut all the .125 cap strips. They were all straight as a result.

[svyolo]

How much force is required to straighten it/divided by the force required of it at utility category. My guess is the bow is almost nothing.