TBU/TBY Wing Fold

Somebody asked for details on the TBU/TBY wing fold area because it isn't covered in detail in Steve Ginter's monograph. Note that there are two hinge points, one on the main spar and one on the forward spar, and a large bellcrank that is driven by two actuators, one in the inboard wing and the other in the outer.

There was one confusing element, an oval panel with pointed ends on the upper surface of the wing over the wing-fold area. The panel was necessary to provide an opening for the outer wing to fold past vertical.

I initially assumed that the panel was metal and part of the outer wing but I couldn't figure out how it didn't interfer with the hinge on the main spar. I finally realized that it was something like canvas (perhaps a rubberized fabric) and simply folded in on itself.

Here the cover appears to be bulging upward from aerodynamic pressure in flight.

This illustration shows the location of the main spar hinge relative to the forward hinge point and the cover

This was the only other picture that I could find of the fold area. It shows the lower half of the wing-fold actuator bellcrank and the inboard actuator.