CB-1 Spar question

[Sarpy Sam]

I'm tearing down a ground looped CB-1. I've discovered on the right lower wing that the top surface of each spar is beveled such that only about half the thickness mates with the rib. I'd like to salvage what I can but am concerned about this deal. Can I shape a small triangular piece of capstrip and place it between the rib and the spar when the ribs are glued down?

[JBMoore]

Interesting question....... so I Googled it!
I found a document, ANC-18 Design of Wood Aircraft Structures, that explains everything you want to know about wood structures... in government jargon.
I cut out some stuff on how to fasten ribs to beams and attached it. It appears the bulk of the strength is along the sides of the spar and not the top and bottom. I built my aileron ribs in this fashion to get as much spar depth as I could and haven't had any problems.
So, read what it has to say and make your own conclusions.
I found the document at http://www.homebuiltairplanes.com/download/ANC-18.pdf.
It's rather large and takes awhile to download.

Good luck and thanks for rescuing a CB-1.

Jeff Moore

[Sarpy Sam]

Thanks for the input Jeff. I got to thinking about this spar and I think the builder(now deceased) simply cut the angle on the wrong side and turned it over and ran it through again. I've found some really bad craftsmanship. I had to clean the mounting pads off the spar with a planer and found extraneous holes drilled in the spar and covered with the pads. I don't know what kind of epoxy he used but the ribs simply fall off the spar. I haven't had to sand one off yet. I found a piece of 1/16" plywood to bush the space between the spar and a poorly constructed rib. It seems to never end. I think the previous owner was very fortunate that he just ground looped and destroyed the airplane. It might have been much worse had he continued to fly it. I actually found one spar and tip bow rotted to the point that it was powder!

Fun project however but am surely a novice. Hope you guys can keep me lined out.

Sarpy Sam

[mtaylor]

Doesn't sound like epoxy to me. Or maybe it was mixed way out of proper portions. A proper glue joint will fracture in the wood, not the glue joint itself. You are smart to get deeper into this rebuild. If those spars have been weakened in any way you'll do yourself a big favor by ordering new spar stock. Have you or can you check what is under the rest of the doublers? It's a strong biplane, but only if it's built right. Just read your post again and it sounds like you'll have to order some new wood anyhow. How 'bout a fresh new set of spars? I may be a little paranoid here, but then I haven't seen your project, just going by what you've said. Glad to have another Hatzer on board and look forward to seeing you fly your very airworthy Hatz into Brodhead in the future. Good luck and glad to see your'e being cautious.

[Sarpy Sam]

Right now, it appears that both spars from each of the left wings are going to be ok. I'll have to remove at least one pad on each to thread new ribs on and if that exposes any more surprises, I think the entire set will be history. I should be able to saw them into capstrips and I'll need a great deal of that! The only reason I suggest that the wings were assembled with a two-part epoxy is because of an entry in the log book. However, the local grocery store sells epoxy as well so we just don't know. It appears to me that the Stits was the only thing keeping the wings in one piece. I'd sure hate to believe that this represents the experimental industry.

Thanks for the feed back.

Sarpy Sam