"...bigger than its belly can"

Of all the engines I am surprised not to have seen made here, the valveless pulse-jet is it. Sure, they're inefficient and relatively low-powered (compared to a "normal" turbine-based jet), but they are astoundingly simple.

At heart, it's a swollen pipe with a fuel supply and no consideration for the neighbours.

These suckers are loud.

So maybe you want to ?

Or just look at the way this engine is mounted, imagine riding it, and shuddering in anticipatory panic.

Picture of
jet scooter 2.JPG