shrouded rotor

In some cases, a shrouded rotor can be 94% more efficient than an open rotor.

Conception DARPA was at first not interested in traditional rotary-wing aircraft, but shrouded rotor concepts might have been considered.

The company said it combines the technical know-how of the proven BK 117 and the EC 145 with new and innovative developments, including a complete tail boom with the Fenestron, a shrouded rotor with eight to 18 blades that increases torque control efficiency and reduces power need.