Pitch is the distance forward one fan blade travels in one revolution
Example: 10/8. 10 inch propeller travels 8" through the air per revolution
at 100% efficiency (no slippage ) No propeller is 100% efficient except
when traveling through a very dense medium. Now, when you complicate the
equation further with factors like pitch that varies throughout the length
of the blade, or fan material that flexes under various loads, or a
condition know as cavitation, or spills air off the end of the blade, or
creates vortexes, it gets funner trying to describe efficiency. It gets
further complicated by fan shroud placement as well as ducting both ahead
of the fan or behind it. Engineers earn their chops on fan designs, for
sure. Other factors enter into it also like safety, noise of operation,
fitment into space available, etc. I had a friend that owned a 289
supercharged Golden Hawk Studebaker that pitched one of it's fan blades off
while running at speed. It went right through the hood on it's way to who
knows where. He lost it at night and never found it. Engine shook like a
hound dog passing peach pits until he replaced the fan.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
> hey Ken,
> Not sure how to measure the “pitch” of the fan,
> and i thought figuring out the “working area” might be easier,
> but my fan has (7) blades that are 4” wide and 7” high,
> so my guess is that this equals 28” of "working area", each??
> multiplied by 7 blades = 196” total working area…
>
> Must be some other way to measure, because regardless of whether they’re
> referring to individual blades or sum of all the blades,
> both specs are out of the ranges that they mention… hmmmm…..
>
> Its looks like a sizable fan to me (i think my ’78 eleganza has a slightly
> smaller one… not sure)
>
>
> > I found this additional information on the the Internet. While the
> numbers are slightly different they do follow the same trend. This does
> include
> > pitch information and square inch information. I do not know what
> "Land and groove design" is.
> >
> > Standard Duty Thermal
> > Turns the fan 50-60% of shaft speed when engaged. Used with fans with
> lighter pitch. (1-1/2" of pitch) Flat plate impeller design with 30 Sq. In.
> of
> > working surface.
> >
> > Heavy-Duty Thermal
> > Turns the fan 65-75% of the shaft speed when engaged for increased
> cooling. Used with deeper pitch fans. (2" of pitch). Land and groove design
> with 47
> > Sq. In. of working area allows higher operating RPM's.
> >
> > Severe Duty Thermal
> > Turns the fan 80-90% of the shaft speed when engaged. Used with deeper
> pitch fans. (2-1/2" of pitch). Land and groove design with 65 Sq. In. of
> > working area.
>
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> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
Example: 10/8. 10 inch propeller travels 8" through the air per revolution
at 100% efficiency (no slippage ) No propeller is 100% efficient except
when traveling through a very dense medium. Now, when you complicate the
equation further with factors like pitch that varies throughout the length
of the blade, or fan material that flexes under various loads, or a
condition know as cavitation, or spills air off the end of the blade, or
creates vortexes, it gets funner trying to describe efficiency. It gets
further complicated by fan shroud placement as well as ducting both ahead
of the fan or behind it. Engineers earn their chops on fan designs, for
sure. Other factors enter into it also like safety, noise of operation,
fitment into space available, etc. I had a friend that owned a 289
supercharged Golden Hawk Studebaker that pitched one of it's fan blades off
while running at speed. It went right through the hood on it's way to who
knows where. He lost it at night and never found it. Engine shook like a
hound dog passing peach pits until he replaced the fan.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
> hey Ken,
> Not sure how to measure the “pitch” of the fan,
> and i thought figuring out the “working area” might be easier,
> but my fan has (7) blades that are 4” wide and 7” high,
> so my guess is that this equals 28” of "working area", each??
> multiplied by 7 blades = 196” total working area…
>
> Must be some other way to measure, because regardless of whether they’re
> referring to individual blades or sum of all the blades,
> both specs are out of the ranges that they mention… hmmmm…..
>
> Its looks like a sizable fan to me (i think my ’78 eleganza has a slightly
> smaller one… not sure)
>
>
> > I found this additional information on the the Internet. While the
> numbers are slightly different they do follow the same trend. This does
> include
> > pitch information and square inch information. I do not know what
> "Land and groove design" is.
> >
> > Standard Duty Thermal
> > Turns the fan 50-60% of shaft speed when engaged. Used with fans with
> lighter pitch. (1-1/2" of pitch) Flat plate impeller design with 30 Sq. In.
> of
> > working surface.
> >
> > Heavy-Duty Thermal
> > Turns the fan 65-75% of the shaft speed when engaged for increased
> cooling. Used with deeper pitch fans. (2" of pitch). Land and groove design
> with 47
> > Sq. In. of working area allows higher operating RPM's.
> >
> > Severe Duty Thermal
> > Turns the fan 80-90% of the shaft speed when engaged. Used with deeper
> pitch fans. (2-1/2" of pitch). Land and groove design with 65 Sq. In. of
> > working area.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
