My googling yields a tensile yield strength for plywood of about 40MPa (much like aluminum). But the density of plywood is only 900kg/m^3 compared to aluminum’s 2700kg/m^3. It looks like at face value, plywood is also viable. I think it’d make for lighter spars potentially. So, we have to keep plywood in mind.
Do they make large sheets of fibreglass or plywood? I wonder if they’d provide better strength to weight ratios over plywood? The cost of sheets would be quite a bit larger.
If it exists, I can get it. I have loads of 6mm (.25") birch plywood on the shop. It’s easily laser cut on my cutters. I can laminate multiple sheets if necessary. Plus it’s a common material if anyone wants to build one of these
On another note, I read up recently on the use of counter-rotating props on electric planes to minimize the diameter of a single prop… Also lowers requirement of length of landing gear. Saves weight.
I like the idea of plywood, being cheap and accessible. Let’s proceed assuming we can make plywood work and see where that takes us. Laminating will be required (or getting thicker sheets).
Sounds great!
I calculate that we’ll need a plywood spar that is 3/4" thick, with a base width of 2". The spar will taper towards the tip of the wing. I’ll send out and update to my spar loading calculation spreadsheet.
Assumptions: pulling 6 Gs, load concentrated 2/3 up the spar, safety factor of 1.4, plane weighs 10kg. Spar is 1.15m long.
I hadn’t considered yet that we’re running a smaller second spar in the wing. This will reduce our requirements a bit. Will try to account for that, but we unfortunately don’t have the man-power to properly assess this and may have to just go conservative.
All sounds great! I’m such a “build it and see” type guy. It’s awesome that you even know how to get us close to reality!
I’ll post a couple pics of some prints 
