I have no way of accurately testing my DF spar caps. I did do something that gave me some personal reassurance my spar caps are strong enough for my XL
I took an 8" long 3/4 x 1" piece centered it under my Crew Cab 3/4 ton GMC truck which has an empty weight over 6 thousand pounds. I placed the bottle jack just to the rear of my front wheel and started jacking up the truck. The front wheel was almost free of the pavement when the Doug Fur separated and bent It on the bottom edge, but did not break into. the wood was severely compressed on each end where it was laying on the bricks. I was very careful to make sure the bricks were not directly under the jack where the wood would only see a compression load. I don't know how much force that was, but I'm confident in my own mind it is more load than my wing will ever see, and it was only one inch thickness of DF. The wing front spar will be 1 7/8" with webbing, bracing and other structural works.
I plan on doing a similar test with a longer piece of wood, maybe a 15" length. The bottom of my bottle jack is around 3" wide.
