OT Efficiency of air propeller versus water propeller?

Are you familiar with the experiment. A water float with an air propeller above the water, connected through a shaft, to a water propeller under the water. Put a fan on the air propeller, and the float moves towards the fan.

Can that be considered a demonstration of the efficiency of an air propeller versus a water propeller? The air propeller is less efficient than the water propeller, that's why the float moves towards the air propeller?

Thanks.

Reply to
John Doe
Loading thread data ...

Correction

Reply to
John Doe

Too many variables. Make the "water propeller" one inch in diameter, and the "air propeller" six feet in diameter -- do the results end up the same?

Define efficiency. Power efficiency? Force vs. size efficiency? Force vs. angular velocity? Number of replies per meaningless post?

Etc.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
 Click to see the full signature
Reply to
Tim Wescott

"John Doe"

** Nope. Was it on U Tube?

** Course not.

** Both types of propeller can be highly efficient - but this requires careful optimisation to the particular application.

For example:

With high speed racing boats, by far the most efficient propulsion is with a prop that has only one half submerged. This is commonly known as "surface drive" and creates a spectacular plume of water behind the boat.

The water entering the prop must be undisturbed by the hull or drive haft - so it is used with hulls that ride right on the surface or twin hull designs that have a central air gap for the prop shaft.

It is efficient because it eliminates cavitation due to lack of smooth water flow into the prop and is further aided by surface tension on the unbroken water as each blade chops down.

Special props are designed for this kind of use.

... Phil

Reply to
Phil Allison

"Tim Wescott"

** With propellers, it is usually take to be the ratio of torque to thrust under given conditions.

There is quite an engineering science around it.

Cos it matters a bit.

... Phil

Reply to
Phil Allison

Regular troll

Tim Wescott wrote:

news.astraweb.com!border6.newsrouter.astraweb.com!news.glorb.com!npeer01.iad.highwinds-media.com!news.highwinds-media.com!feed-me.highwinds-media.com!border3.nntp.dca.giganews.com!Xl.tags.giganews.com!border1.nntp.dca.giganews.com!nntp.giganews.com!local2.nntp.dca.giganews.com!nntp.web-ster.com!news.web-ster.com.POSTED!not-for-mail

sv3-aGlvkE13/yFybTyDEKp/eCZsYV88N1ijGmKHxA3FgU11mf7hk5lQe34KUxkiaS/3cesXOzsNMa9CcVa!2rWSaMRFKDhCoGqApVjeAmx6XWgMaTeJF+jMmPfT/8Axr9ttkc8xub7n67NGpzVEnYuwtybdpDOk!pVA1EAozF/yN15o=

properly

Reply to
John Doe

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.