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2: An open propeller with slipstream contraction & Ducted propeller with diffuser section
The VLJ is an advanced ducted propeller combined with a stator positioned in the duct aft of the propeller, in a similar arrangement to that of a waterjet.
Little information is available on the Piasecki Pathfinder IV, a compound helicopter with the company's patented Vectored-Thrust Ducted Propeller (VTDP) at the rear end.
The Deutz engine turns a ducted propeller in its own housing.
Other innovations include ducted propellers, skirt shift control systems and lower noise levels.
The only compound helicopter concept currently funded by the Defense Department is called the Vectored Thrust Ducted Propeller (VTDP).
The VTDP has fixed wings and a rail-mounted ducted propeller.
The tail-mounted ducted propeller, called the ring-rail, provides auxiliary thrust and control in forward flight, Piasecki explained.
Dr Thompson added: "Investigations have revealed a number of features that show the injuries are entirely consistent with the animals being sucked through large ducted propellers.
In principle, ducted propellers or fans require far more power than a helicopter, but offer higher speeds and better compatibility with urban operations.