RE: Nitroplanes 90" P-38 (1/7 scale) with 3 piece wing and more
Put springs on the hinges. I drilled 1/32" holes in each hinge half, used ball point pen springs cut down to 3 coils, bent each end to insert in the drilled holes in the hinges.
Bolted the hinge halfs together, rotated one half 360 degrees to put the spring under tension, then attached the hinge into place. Automatic self opening doors. [)]