Known as the Russian K7, it is reported to have flown 11 times before crashing. At least that is the story I saw. I don't think the could fire the canons simultaneously in a broadside.
I guess it is just a mock up of some design that really never flew. The actual K7, which was un-armed and smaller, did fly. I'll have to talk to my usually reliable source.
The gun trurrets look similar to the ones on late WWII U.S. heavy cruisers (8" guns). That would make the turrets weigh in at around 600 tons, plus the ammo and handling equipment.
Lotta load for 20 maybe 600 HP engines (unless only one engine drives both the tractor and pusher prop in each nacelle). It might need a 5 mile runway ending at a 1000 foot cliff. Think how long it would take to start and warm up and then do mag drops.
I remember hearing pilots (on TV) talking about the wart hog feeling like it stopped in midair when its main gun went off. I wondered what kind of velocity change it went through.
I could see the report on the German aircraft, both target and aircraft were destroyed.
I can say that a 5" gun will cause some jolts and motion in a space (room) about 200' forward of the mount when it goes off. That was on a 8000 ton cruiser.
Many years ago, I witnessed an A7 Corsair II fire its 20mm M61A1 Vulcan six-barrel cannon on a mock strafing run. The M61A1 had a rate of fire of around 6,000 rounds per minute. The pilot fired off about a 2-second burst, and it looked like he'd jammed on the brakes in midair!
Biggest artillery I've heard of being installed on aircraft is the 105 Howitzer on AC-130's.