Rotary‐Wing Aircraft: The Second of a Series of Articles Summarizing the Current State of Knowledge Available to Purchase

THAT the rotaplane rotor is essentially a windmill has hitherto been regarded as self‐evident. It will be shown in the following analysis that, when the profile drag is sufficiently small, only part of the rotor is in the “windmill brake” state. This part receives more torque from the air than can be expended in profile drag and therefore the rotaplane rotor at zero torque must be partly an airscrew in the “vortex ring” state.