selfshadowing , the way it is implemented in CloD, works because you have one object (canopy frame object) that casts shadows on another object. (cockpit panel object)
Objects that are, from a modeling point of View, closed like a cube, having all 6 sides. or a tube having the side polygons AND the top and bottom cover.
In Il-2, the Objects are not recognized as separated, and the parts that would cast a shadow on another part are not closed.
The polygons are "see-through" from one side (very well visible in PoV mods or in 6DOF) and the objects are not closed.
selfshadowing
a) is not possible at the time
b) the moment where it becomes possible, please redo every cockpit and plane to use it.
fill the Polygones that are missing everywhere, from canopy, Gunsight, Pedalsm stick, walls, Wings (when the wings cast a shadow inside the pit , they need to be complete from every side as well)
Make sure the Plane that is supposed to use this is also complete/integer from the outside (wings cast a shadow on a Gear, gear casts shadown on a wing when flying inverted, elevator casts shadow on fuselage, on rudder, on tail assembly, moving surfaced cast shadow.
you want selfshadowing?
redo the cockpits, basically from scratch.
you want selfshadowing on the outside?
also redo the planes.