Once upon a time I wanted to build a flying car. My idea was to mount propellers on a dozen or so lawn mower engines and arrange them in a ring around a central control / passenger pod. I liked the concept for two reasons. One: lawn mower engines are cheap, and two: if you have a dozen of them and some of them fail, the rest should keep you aloft, or at least keep you from plummeting like a stone.
Also got the idea from an office building I worked at in Austin. Most office buildings have some kind of heating and air conditioning plant, a dedicated space full of boilers and pipes and an old, fat guy in greasy coveralls, sitting around, drinking coffee and reading the sports page. This place didn't. Instead they had a bank of like a dozen household type central air conditioning units, all lined up in a row. I'm sure I have run into numerous other instances of where several copies of a smaller mass-produced machine have taken the place of one giant, custom machine, but this is the one I remember.
I never did anything about building a flying car because it would have required spending money Even lawn mower engines cost more than a dollar and half, and I figured that even if it worked (of course it would have worked. Getting it off the ground would just be a matter of a couple of minor implementation details.), the Feds would frown on my taking off from my driveway, and if you can't fly directly from your house, well, why bother?
Anyway, it looks like somebody stole my idea and then dared to actually build one. It only has eight engines, not 12, and while they might be lawn mower engines, they are from some big, stinking, lawn mowers. I'm guessing they are probably close to 200 horsepower each, which means your fuel bill is going to be in the dollars-per-minute range. But hey, it's the military, big fuel bills are kind of a given.
There is a video of a model of this machine flying, but no video of this one getting off the ground. There is a still photo of a four engine prototype, so I'm gonna give them the benefit of the doubt for the time being. It will be interesting to see if they manage to compete with regular helicopters, the ones that cost zillions of dollars.