This may seem obvious to more experienced builders, but I want to get it right. I'm building a large scale A-10 from plans, i.e. no instructions. The fuselage sides are 1/4" balsa with a 1/4" ply doubler around the wing cut-out. Unless I'm mistaken, I'll have to splice the balsa sides somewhere since the lengths are limited to 36". The attached sketch shows three locations where I could put the splice, but each has pros and cons. Since the side panels are almost 70" long, the overlap area where the splice would go is actually fairly small, so the issue may be moot. Then again, maybe I should put a solid sheet of 1/4 x 36 centered on the wing cut-out with splices fore and aft.

Any advice will be most appreciated.

Thanks,
Paul

You could always put the join centered around A, but make the join diagonal instead of vertical - that gives you a larger butt-join area for the balsa.

Gordon

Very good point. Obviously, I hadn't thought of that. I don't like the idea of butt-joints fore and aft. I would have to add more side doublers and weight.

Thanks.

Why not order some 48" balsa.

What about something like this???

Chris

I have to admit that I missed the availability of 48" sheets. So far, I have only looked at few suppliers. SIG, for whatever reason, put 48" under a different category than basic "balsa sheets." The plans don't show any joint at all, so I thought maybe I had missed the availability of sheets 70" or greater.

Thanks.

Good suggestion. I think I'll be using it. I know that joint design has a name, but for the life of me I can't remember it. "Cabinet joint," or something like that?

Thanks much.

Try Lone Star Products, they have everything and fast service at the best prices anywhere. I have dealt with them for yearsI think all balsa comes into the US in 36 or 48" chunks ,3x4 or4x6". No logs, as they killdry it there, to save weight and scrap.

Thanks for the lead. I'll check them out.

Paul

Thought I'd save you some trouble...

http://www.lonestar-models.com/

Thanks for the tip, bjdbair & JohnnyA. I just tallied up the cost of the wood I need to complete my project and nearly had a cow. However, I took a look at Lone Star and they came in at less than half of Brand X. I have never bought balsa or ply bulk before (although bulk is a relative term, I guess). As long as it's rated AAA, can I assume that the quality of balsa from Lone Star and others is a good as some of the more well known brands found in hobby stores?

Paul

I've gotten a few bundles of balsa from Lone-Star. IMHO, I think Midwest is a cut above. I've since switched back to the latter. But, I'm a quality freak. Use watcha like. My 2 cents.

Steve

Paul,Just a word of caution.Being a full scale structural aircraft engineer for the last 30 years .I would not put a splice in any area for the wing cut out.This would be not a approved in full scale,due to the integrety of the joint.With a plane the size you are building I wouldn't trust it.Try and go with 48 inch material.If you do decide on the scarfe joint.Splice it at the front of the leading edge.Think it was point "B". Use a 4 to 1 ratio for the splice.and going forward Hope this will help you.

You had indicated that you will be using balsa will a plywood doubler.

I would overlap the splice point so the splice of the balsa, and plywood are not at the same location. This will give you maximum bonding area. This in effect is laminating wood together which yields a stronger construction than a single piece of wood.

Brian,

Thanks for the advice. I will need to move the splice from that very thin area at the center of the wing, which is where it would fall with 36" sheets. Using 48" from the rear, I could move the splice off the wing altogether. This would mean using another ply doubler at the splice, but maybe that's best. The current ply double only covers the wing and about two inches fore and aft.

Thanks again.
Paul

Thanks for the note, Six Shooter. In this case, the ply doubler only covers the wing cutout. I wanted to keep the balsa splice somewhere on that doubler, but I'm thinking of moving it forward as indicated in my reply to Brian above. I'll use another ply double under the splice.

Paul

Hmm, also an engineer, and also having a big A-10 kit (fiberglass version) there are various ways around this.

First, I don't see why the balsa joint has to be over the wing even using 36" lengths. THe chord of the wing is not over 36" so obviously a single piece could span it.

However, with a 1/4" plywood doubler( I assume it's a one piece doubler) and a good scarf joint there is no real risk whatsoever from putting the splice over the wing. If you want some insurance, put some structural fiberglass (as opposed to lightweight cosmetic stuff) over the joint on the outside. If you like spending money, upgrade to CF.

If you want the best scarf joint, angle it not only from the vertical, but also thru the thickness of the wood. That would require precisely matched cuts in each piece using either a jig or a good bit of sanding to fit.

Lastly, I'd like to hear the $$ amount you plan on spending for balsa & ply here. If it's a whole pile, you'd be better off buying the glass kit from Dean Lassek for around $1500.

Initially, I thought only 36" lengths were available. I thought that spanning the wing cutout with one piece would mean two splices, fore and aft, adding weight. Using a 48" length from the rear, I'll move the splice forward and use a ply doubler underneath.
I had the shaped parts (ribs, formers, etc.) laser cut from the plans. The rest (spars, sheeting, leading/trailing edges, etc.) I have to buy from a supplier. Right now, I'm looking at a total wood cost of around $350 for all of the above. If I'm not mistaken, Dean's kit is for a larger model, driving costs up all around (mine has a wing span of 78"). In fact, I don't think I ever found Dean's or any other kit in my searches. I would have preferred a kit, but couldn't find any (other than Combat Models pusher-prop version).

I didn't want to make too big of a deal about this one building issue, but I did hear about some structural concerns in the wing area with this design. In fact, the width of the balsa just above the wing cutout is only about 1", maybe a bit more. It's seems to be fairly weak already.

Anyway, I appreciate all of the good advice.

Paul