I don’t understand why these rotary wing aircraft are not ducted.
Efficiency, weight and added cost.
The drag penalty and increased complexity probably doesn't offset the gain in efficiency of the props.
“I don’t understand why these rotary wing aircraft are not ducted.”
Fixed wing.
These propellers are pretty large reducing the duct advantage. Ducts would add weight and possibly interfere with assembly rotation.
“I don’t understand why these rotary wing aircraft are not ducted.”
Ducted propellers (
Kort nozzles) offer higher efficiency and increased thrust at low speeds, heavy loads, or static conditions by reducing tip vortices and utilizing shroud lift. Conversely, unducted (open) propellers are generally more efficient at higher speeds, as the duct introduces drag that outweighs its thrust benefits.
Actually in flight the unducted is more efficient. The ducted is more efficent (about 7%) in a vertical lift. Thus that advantaged is negated by extra weight and drag.
The aircraft in question is not a rotary wing aircraft such as a helicopter. The whole wing rotates for vertical lift and then rotates back to normal position for flight and the reverse for landing.