strength of aircraft ply vs regular plywood

I bought some 3/8 aircraft ply from Aircraft Spruce for fins, thinking it would be strong enough and save weight over regular 1/2 inch ply. The 1/2 inch is good birch 7 layer ply from Menards. Turns out they are almost exactly the same weight.
The aircraft ply should be stronger for a given thickness, but a 1/2 inch fin is certainly stronger than 3/8.
I'm not concerned about drag - it's low and slow anyway.

So what do you think, since the weight is the same, which would be stronger?

Granted, I'm guessing, but I would say the thinner. Just stands to reason that higher density would infer less void space, and greater resin penetration during the ply making process. It probably wouldn't be hard to do a quick and dirty load test on a small rectangular piece. I for one would be very interested in your findings.

Most domestic and import hardwood plywoods are only hardwood veneers over lesser woods. Baltic Birch and AC plywoods on the other hand are all birch plys.

I would try to make your own plywood out of 1/64" thin birch and use wood glue and a lot of weight to press it all together. With that thickness of thin birch you could laminate together a 1/4" thick fin that would be far stronger and lighter than the 1/2" or 3/8" stuff you are planing to use. It's a bit of work, but quite doable.

True Baltic Birch Plywood is 5-ply for 3mm, 6mm, 9mm (1/8", 1/4", 3/8" nominal), 9-ply for 12mm (1/2") and 13-ply for 15mm and 18mm (5/8" and 3/4"). I need to correct my earlier post in that Aircraft Birch Plywoods are usually birch veneer faces with another wood like basswood or poplar as the cores (which will help with weight).