How ducting a propeller increases efficiency and thrust

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.

Видео How ducting a propeller increases efficiency and thrust канала RCModelReviews