Why would you need an aircraft with 18 rotors? The Air Force is exploring this and many other aircraft for potential battle field applications. A craft that can be stationary with medium altitude could serve one soldier and a a weapon very well. Cargo, spy equipment, armaments, and a lot more.
In the case, the Hexa is electric. It doesn’t fly very well yet. Needs a lot of work. But the Air Force is interested.
Something with 18 rotors could probably be very survivable. Lose 1, 3 or 7 rotors, and you could still be in the air.
It is an interesting invention.
I want one (when its finished, not now, the damned thing barely flies…)