Perpetual mobile vs time machine
It seems that the Northern Ireland business tax exemption authority learned little from DeLorean.
Why did the hand-cranked vacuum-cleaner-powered bicycle never catch on?
It's basically a Harrier with the two cold exhausts spinning round and round. Doesn't sound tremendously fuel efficient.
Clever shaping might reduce the noise to acceptable levels, but good luck with certifying it to deal with a blade-tip bird strike.
There's a good reason that the NOTAR vent is at the end of a boom.