Talk:Kort nozzle

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Physics seem wrong[edit]

I don't think the physics explanation is correct. It essentially says that flow circulation increases thrust. That is nonsensical. An unducted prop would create even more circulation than a ducted one. Rather the duct improves thrust because it reduces circulation and the drag it causes. The ducted fan article says something similar. "By reducing propeller blade tip losses and directing its thrust towards the back only, the ducted fan is more efficient in producing thrust than a conventional propeller, especially at higher rotational speeds." Dude6935 (talk) 07:02, 9 February 2010 (UTC)

You're correct that the physics explanation is incorrect, although your explanation of why the Kort nozzle increases lift isn't correct. The nozzle is a cambered hydrofoil wrapped into a cylinder (with the camber facing inward). The prop accelerates flow over the "top", or inner side, of the hydrofoil which, because it is cambered in toward the center (and has an apparent angle of attack from the kort nozzle page's diagram) causes a lift force vector that points toward the axial symmetry line and has a positive axial component (ie: in polar coordinates, there's a negative radial component and a positive axial component)[edit: the kort nozzle diagram shows a "dL," but doesn't explain it]. The cylindrical nature of the hydrofoil causes the radial components to cancel , and the resulting force is in the positive direction.

So, in addition to the thrust gained by adding momentum to the water with the prop we get thrust from this lift vector. I can't speak for hydrofoils, but I know ducted rotors in aerodynamics (such as ducted tail rotors on helicopters) can end up having 1/2 of their thrust come from this lift, while the other 1/2 is from the addition of momentum.

This is my first wikipedia contribution experience, so if anyone sees this and believes some form of it should be added to the article, let me know. I don't know the precedence for when one should edit an article. Ianohara (talk) 13:34, 1 June 2011 (UTC)


I would say yes to merging the two articles. I am not a subject matter expert, but they appear to be almost identical. Mikevpol (talk) 15:19, 19 May 2011 (UTC)