Re: 5 blade cooling fan mod

[Tony Lum <tlum@flash.net>]

At 07:33 AM 8/7/98 -0600, you wrote:
>I thought that this might be relevant to you modification.  This is a
>paragraph from "The Design and Tuning of Competition Engines" by Philip H.
>Smith, published by Robert Bentley Press.
>
>    "Multiblade fans are quieter that two blades fans;  sometimes
>multiblades are set at irregular angles to one another to limit the further
>the possibilities for resonate frequencies that passengers might find
>objectionable.  In a competition car, therefore, it is often possible to
>reduce fan drive losses  by using  a fan with fewer blades or a smaller
>diameter"
>
>It continues to discuss horsepower losses due to fans in the later
>paragraphs and makes these points.
>
>1.  Electric fans are used over belt driven fans due to fact that electric
>fans are tuned to a specific RPM making them much more efficient to use.
>
>2.  The main reason for using multiblade fans is not to increase airflow but
>to eliminate noise.
>
>So any fan that was designed for a higher air flow will help in cooling
>regardless of the number of blades so long as the engine RPM and the fan RPM
>are designed to work together.
>
>mark@anetinc.com
>
Those are fascinating observations.  I wonder how that relates to aircraft.
 I recall that the prototype Spitfire (help me out here, Phil) had a two
bladed propeller, while the production version we're all familiar with used
a 3 blade.  The P51 Mustang used a 4 bladed prop and I'm sure the designers
weren't too concerned with noise.




-Tony
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Tony Lum                                  1987 5000CS Turbo Quattro
Berkeley, California, U.S.A.                1985 4000CS Quattro
Audi Owner/Driver/Mechanic by Necessity ;^)   1980 5000S Sedan
                                               1987.5 Coupe GT
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