This is a Notable Operational milestone.
This was a single place 25 foot (7.6 m) diameter coaxial rotor helicopter having an enclosed tube and fabric fuselage, powered by a single 100 hp (75 kW) Continental C-100 engine. The prototype did not, originally, have an eclosed fuselage.
Source: "Helicopters, Inc./Bendix Helicopter, Inc.
Bendix Model K", Pete Noell, AHS 2018 VTOL History Calendar - June