I managed to get a spreadsheet to very nearly match the values I calculated yesterday

***** and then adjusted for the 40% load on the rear wing (and not applying all the lift to one wing panel--doh!). The stresses are lower than before--we know this because the max. shear and bending values are lower on the diagram below. The rear wing looks plenty strong. If you end up having weight problems, the spars could potentially go on a little diet (perhaps a few pounds?).

I've also persuaded myself that the interrupted shear web can be acceptable. If we round up the max. shear to 400 lb, then each of the "stubs" is carrying 100 lb shear over a cantilever of 1". Both the shear and bending stresses resulting from that cantilevered point load are pretty low. The moment carried by the wing (say 4,500 in-lb at station 44.49", the slot with the highest moment that's nearest to the strut) gets resolved as a couple in the upper and lower cap "stubs" with an axial force of about 900 lb. I have to admit that I've never done combined bending and axial using Bruhn's methods, but these stresses are off the low end of the FPL charts. Also your stress at the glue line between the caps and webs is quite low.

I would feel better, though, about adding some small vertical wooden stiffeners on either side of the webs where they touch the foam; relying on the bond to the foam on the thin edge of the plywood might not be best practice as a stiffening device, but the proof will be in the test, not Some Guy on the Internet With an Opinion (like me).

*****I used a rather crude method to integrate lift to generate the shear curve, and then once again to integrate shear to generate the moment curve. The inaccuracies get magnified at each step, but I'm pretty confident the end product is within 5% or so--WAY less than the margin of safety you have here. You can tell there's a problem in my method since the moment curve doesn't quite return to zero at the left end. (The shear curve does not return to zero at the left end because of the small reaction at the fuselage attachment. Sometime I need to tinker with a way to do real integration in Excel and this would be more precise.

One way you might be able to save some weight is by attaching the strut further out. Of course, this makes the strut floppier in compression and adds to axial stress in the spar--there are always trade-offs. But notice how the diagrams change (lower max. shear and moment) if it's moved out to 1.2m (here again you see the non-zero problem at the left end of the moment diagram, but this is just a conceptual comparison):

Also, thanks for your kind words, but in truth I'm just a hack with a stack of books and a calculator.

My opinion here is worth what you paid for it--trust your tests and not me.

I should be able to run the front spar relatively easily now with the spreadsheet. What does the support look like? One center point and a strut on each side, or just two struts? Similar rib spacing? I assume the front is a one-piece spar.