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Old 12-24-2010, 11:23 PM   #6
JetPlaneFlyer
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I think 'fan' and 'prop' are really just semantics.
  • By definition a fan is a device to move air
  • By definition a propeller is a device which reacts with air (or water) to create forward thrust.
In reality they are both the same thing because you cant create thrust without moving air and vice-versa.

Anyway... your homebrew fan looks like it's very inefficient in terms of how much thrust you are getting for the power consumed. A commercial ducted fan would get about twice the thrust for the same power and a normal prop would be at least three times more thrust.

I think your fan is losing out at least in part because you don't have any stators. Stators are the vanes that you see on all commercial ducted fans, usually mounted just behind the fan itself. They are shaped and angled to convert the swirling air coming off the fan into additional forward thrust. They also serve the purpose of holding the fan and motor central in the shroud.

Generally even the best ducted fans are less efficient in terms of static thrust than ordinary props; this is mainly because for a given input power they are usually smaller in diameter than props. Prop/fan efficiency is closely related to diameter, bigger diameter is more efficient. Small diameter ducted fans will always tend to be less efficient than props given the same input power.

Steve
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