Me 109 and cannon trough prop-shaft

[ArtieBob]

IMHO, your problem in understanding is that the gun is not "inside" the engine. The breech mounting was aft of the engine crankcase and cylinder with the barrel and blast tube run between the cylinder bank vee. In the late Bf 109s, I believe the breech of some weapons extended into the cockpit to the point that rudder movement was impeded. The engine has a reduction gear which offsets the propeller centerline vertically from the crankshaft. The prop shaft is hollow and sealed so the gun is isolated from the engine internals, fluids, etc. If you look closely at the H-S drawings, I believe you can make out these features. Of course the DB engines were inverted vees, but the concepts are similar.

Best regards,

Artie Bob