Back in World War I, getting a machine gun to fire through the spinning propeller of an airplane was a challenge.
Some fighters even had armored props to keep stray bullets from sawing through the blades. Later a cam, affixed to the inner workings of the propeller shaft, stopped the gun from firing at the wrong millisecond as the blade passed in front of the muzzle.
The FHC’s Fw 190 has machine guns and its inner set of cannons situated behind the propeller disk as well. By World War II, most “interrupter gears” actually evolved to electrical cut-off switches that broke the firing circuit to the weapons and paused their discharge for a brief moment.
You can come and see the Fw 190, Bf 109, and Storch up close on the FHC’s next free Fly Day, Luftwaffe Day August 16th. Planes fly at noon!