How ducting a propeller increases efficiency and thrust

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By placing a propeller in a duct, the efficiency and maximum thrust can be increased, sometimes significantly. This video explains two of the mechanisms by which these improvements are obtained — namely by reducing the losses due to the tip vortex which occurs when a propeller operates in free space and also by using an annular wing that harnesses the effects documented in Bernoulli’s theorum.

Original YouTube post

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