The wing spar that was impossible to assemble has passed its ultimate test. This was a really important milestone, more important than the first flight. We knew it was going to fly and we had enough analysis and simulation done to know what it would be like to fly. But this spar test was a much bigger unknown. We truly didn't know if it would pass the test.
Two years ago, we knew we had a problem. The spar design as drawn could not be assembled. "Tab A, slot B" looked OK on paper but on the actual parts, cutting the slot would leave no actual spar material to carry the load and engage the pins.
One year ago, Airbus helped us find some FEM experts. We measured the spar up and down, inside and out. We knew exactly what was built and exactly how it differed from the original design. We gave them our best attempt at designing a cure and their response was: "You have to test this. Our computer model can't predict exactly what will happen." To be fair to the FEM guys, we only gave them a couple of weeks to look at something that was completely outside of their experience in other engineering fields and they donated their expertise for free.
This week, after carefully loading almost three tons of sandbags onto the wing, we took away the supports and the wingtips sagged to within just a few inches off the floor. It held! The controls could be operated normally while loaded. The deflection - almost fourteen feet in total - was only two inches less than the prediction from our consulting engineer.
* Extra geek points to anyone who knows the two Doctor Who episodes I'm referencing in the title.