It is powered by two jet-turbine engines which operate both the five-bladed main rotor and, through a gearbox and shafts, a pair of propellers on two short wings.

One way to increase the efficiency of a high-bypass jet engine is to turn the fan into an open rotor, a bit like returning to propellers, but using two rings of stubby counter-rotating blades.

There is another way to build a greener jet engine: by bypassing the turbine to an even greater extent, with an open rotor.