>Date: Thu, 1 Jul 1999 08:04:30 -0700
>From: "Jay Laifman" <Jay_Laifman@countrywide.com>
>Subject: Fan Blades
>
>
>Here is something I'm sure Bob and my dad will not leave untouched. In
>today's LA Times, in the "Science" section they had the following:
>
>"Q: Is a fan with five blades more effective than one with three
>blades? A: The more blades a fan has, the less efficient it becomes
>because each blade is moving in the turbulent wake of the blade
>preceding it. But a fan with fewer blades has to turn faster to move
>the same amount of air, so it will have a higher tip speed and thus be
>noisier. The same principles apply to airplane and ship propellers.
>The optimum efficiency is achieved with a single blade attached to a
>suitable counterweight, and some planes have actually flown with such a
>design. The primary reason for multiple blades is to reduce the
>diameter and the noise."
>
>
>Jay
Ah, I get it. The reason Spitfires had 5 bladed props was so they could
quietly sneak up on Germans.
Roland
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