Stop-Rotor Rotary Wing Aircraft

Some unmanned aircraft designs attempt to combine the vertical takeoff and landing (VTOL) and hover capabilities of a helicopter with the increased speed and range capabilities of fixed-wing airplanes. Stop-rotor “nose-sitter” configurations — so named because the aircraft takes off and lands from a nose-down orientation — may offer good hover efficiency and aerodynamic design, but can require complex mechanical systems. These designs can also suffer a significant loss in altitude during transition from helicopter to airplane mode, and involve uneven weight distributions, rendering the aircraft “top heavy” and unwieldy during takeoff and landing. Further, the counter-rotating fuselage and tail of some nose-sitter designs are less practical than aircraft designs with a conventional fuselage orientation and tail rotor. Tiltrotor configurations with tiltable rotating propellers also involve mechanically complex systems and decreased hover efficiency due to higher disk loading. “Tail-sitter” designs — so named because the aircraft takes off and lands from a tail-down orientation — are associated with poor hover efficiency due to high disk loading and an awkward 90-degree attitude change between hover and forward flight modes.