In order to fly a number of single rotor units join up with one another to form a viable aircraft. Individually the units are unable to fly but this changes when they join up and co-operate in order to fulfill their mission.
More details - and videos - can be found here.
Plasma technique converts landfill methane to jet fuel
Trevor; there are still many landfill sites in the UK where the methane is not captured but not only that, where there is protein waste in them, they...