The US Army Air Corps did a trial with basically the same concept in the late 20s/early 30s. They used a total of 50, ten rows of five, M1928 Thompsons (drum magazines, and with all the wood furniture to boot!) mounted in the belly of (believe it or not!) a Ford Tri-Motor, firing downwards at varying angles, both fore-and-aft and side-to-side, to cover a large patch of ground with each pass. Nothing much came of it, since the effective range of a .45ACP round is MUCH less than the effective range of, oh let's just say....just about everything intended for AA use?
The basic idea was for the plane to fly along above the trench line and fire downward, spraying 2,500 rounds of .45ACP in mere seconds, scything away dozens, if not hundreds, of soldiers with each pass. The actual firing tests revealed that the aircraft was basically a sitting duck due to its slow speed, but going faster just made the whole thing less effective. Plus, it was pretty much impossible to reload the Tommies given the way they were mounted.
One of the little individual chutes for ejecting the spent brass from the plane (one per gun), an INTERESTING little piece of metalwork, went up on eBay about 2 years ago. The last bid I saw on it was solidly in the $1,500 range.