Re: 5 blade cooling fan mod

["Mark Rutherford" <mark@afnetinc.com>]

Good point now I am curious.  The only difference in the two application I
can see is the Spitfire and P-51 mustang props are designed to be used at a
variety of RPM's.
While a electric cooling fan is only used a specific RPM.   Anybody know the
relationship between #of blades, diameter, pitch, and RPM for a fan.

mark@afnetinc.com

-----Original Message-----
From: Tony Lum <tlum@flash.net>
To: Mark Rutherford <mark@afnetinc.com>
Cc: quattro@coimbra.ans.net <quattro@coimbra.ans.net>
Date: Friday, August 07, 1998 12:28 PM
Subject: Re: 5 blade cooling fan mod


>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
>_______________________________________________________________________
>
>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
>_______________________________________________________________________
>
>