ok as you clearly see, it still seems to be possible to set spits on fire with only B-Beobachtung....but its hard, and if you dont achieve this effect, so that the pilot burns to death,...B-Beobachtung seems to be not recognized by the game to have destructive effects...
in the meanwhile while the vid was uploading to youtube,...i shot down about ~20-30 spits with only B-Beobachtung...
the result was, that the pilots bailed out once their tailwheel was set on fire...it happened as well, that sometimes smaller surfaces on the wings catched fire(only very small)...and when the spits finally crashed, i got no credit for the kill...i only got credit when i achieved to set the spit completely on fire...otherwise no credit.