Any comments or pros/cons of 1/16th Domestic Birch vs. 1.5mm Finnish Birch plywoods? How do you choose? Flip a coin either will do just fine? They both claim to be the best, and I think I can boil either of them but thats not really what I want to do. Both 3-ply but I think the Finnish birch might be a birch core vs polar in the domestic Birch?

My 2 cents FWIW.
Domestic birch is heavier but less expensive. I used domestic birch for my spar webs on the wings. Realized my mistake after the spars were done because the spars came out a bit heavy. For the leading edge wraparound I purchased  and used Finnish birch, and saved some weight. To me, the domestic seemed stronger,  but then it comes with the weight penalty.

Also I found domestic birch harder to bend to get the shape of the leading edge wraparound. It is less pliable than Finnish birch. I took thickness readings with a caliper, and found domestic was a tad thicker than Finnish for the same 1/16 ply. I had purchased both from AC Spruce.

IIRC, the domestic was 1.7 mm thick, whereas the Finnish was 1.5 mm thick.

Thanks Keith
From your comments I considered Using domestic for strength in the spars and Finnish for the D-cell but in the end I ordered all domestic.
What do you mean your spars came in a little heavy? Is there a target weight published somewhere you compared to?

Flydog, What actually happened was I had purchased some domestic birch ply 1/16 from ACS, as my initial plan was to scratch build a 1100R.

Subsequently I bought a Max 1030 project (which was partially done, from a 20 year old TEAM-supplied kit), from a guy in Alabama. The fuselage and landing gear were done. The wings were not built, but the kit had spruce cut-stock and the 1/16 ply panels for the wings. The ply in the kit was more pliable and a tad lighter than the domestic birch ply that I had purchased from ACS.

I had presumed the ply panels for the wing that came with the kit were lighter because they may have deteriorated with long storage. That was not the case. I learnt subsequently that TEAM had shipped Finnish birch 1/16 for all the wing panels along with the kit. Finnish birch is lighter for sure, and more easy to bend for the leading edge.

There was no target weight for the spars, but since TEAM had shipped finnish birch 1/16 for the spar webs and leading edge, I concluded / inferred subsequently that my spars could have been lighter if I had used the ply supplied with the kit for the spar web.

Regarding leading edge box, I tried bending the domestic birch after soaking in water for a good 24 hours. But it was still hard to bend, and I ended up damaging two domestic panels in trying to bend to D shape. That is when I decided to go for finnish birch for the ldg edge. I used 4 Finnish birch panels from the old kit, and since the remaining two had water stains on them, I ordered two new ( 4x2 x 1/16) Finnish panels from ACS. Shaping the leading edge with Finnish ply, was a walk in the park.

But I am sure some other builders out there, must have definitely used domestic birch 1/16 for the ldg edge box.  Especially if you are not building Pt 103, and weight is not a major limiting consideration, I find no reason why you cannot use domestic birch for the ldg edge box. May be I did something wrong while bending it to shape.

I just looked up the old weight records that I had kept during the build.

The weight of 1/16 plywood is :

34 oz for the domestic birch for a 2x4 panel   ( 4.25 oz per sq ft )

27.6 oz for Finnish birch for a 2x4 panel        ( 3.45 oz per sq ft )


Since front spar uses approximately 6.64 sq ft of ply , using domestic will increase weight by 5.4 oz than when using Finnish. That is just for 1 front spar on one side. For rear spar the weight increase is 4.15 oz per side.

So we are looking at about 1 lb and 3 oz more weight (for all 4 spars together) when we use domestic birch in place of Finnish birch.

In my post above, I had used 1/16 in and 1.5 mm interchangeably.
That is a mistake.

1/16 in is actually 1.5875 mm. So the domestic birch 1/16 in ply is closer
to 1.6 mm than 1.5 mm.

The plans call for 1.5 mm plywood for the wing spars and leading edge box.
So from that perspective, 1/16 in is over-spec for our application, especially
for the Max 103 or 1030.

Separately, on Legal Eagle (which has almost similar wings and wing loading),
the leading edge is made with 0.8 mm plywood. I think Lake-Harley had also
used either 1mm or 0.8 mm for the leading edge box on his MiniMax.
I think his was one of the truly legal 103 Maxes. Just by using a thinner ply he
may have shaved off a cool 2 to 3 lbs pounds off the leading edge.