bearfoil
The Valkyrie had a nifty feature that drooped her outer wing, moving a wing 90 degrees loses all drag due Lift, and we are left with parasite, retaining all cargo and systems volume.
The wing didn't fold down 90-degrees. The wing could be folded down 25-degrees or 64.5 degrees on A/V-1 (On A/V-2 it could be folded down 30-degrees and 69.5 degrees due to the aircraft having a 5-degree dihedral).