<VV> Conditions for cooling fans > Astro 1 engine fans

[Jim Simpson]

I don't think efficiency and fan horsepower are necessarily directly
related.  I can imagine one design of a fan drawing 27 hp and not doing
much more than stirring the air whereas another design may move huge
volumes at high pressures and be very effective at cooling an engine.

So the real question that I have is "Were the fans on the Astro 1 engine
delivering significantly more cooling than any of the prior stock designs?"
Or in other words, did they use the hp more effectively than the stock Corvair
fan?

I suspect, although I don't know, that the moment of inertia of the Astro 1
fans is higher than the late magnesium fan.  But it may be pretty close --
or even lower.  The diameter of the fans on the Astro 1 seems fairly small
so the mass is close to the center of rotation.  That reduces the moment of
inertia -- it's a mass x r^2 issue.  So having three fans half the diameter
of the stock fan would still have a lower moment of inertial.  And I'd
imagine that having a fan belt that didn't change planes would be easier to
control if you wanted to allow it to slip.  (And I'd imagine it would be
easier to engineer an overrun clutch on the Astro 1 fan design.)

Jim Simpson

On Tue, Mar 19, 2013 at 11:40 AM, BBRT <chsadek at comcast.net> wrote:

> There are a couple of issues to consider.
> 1. For a street car, low speed, heat soak has to be overcome. Similarly a
> race car at slow pace, like under a yellow or on the grid.
> 2. For either a street or race car, roatating weight, momentum and inertia
> are important considerations for acceleratiing.
> 3. For a race car, high rpm cooling is a must. High rpm  is > 6500 rpm -
> Observations indicate engine load in 4th at high speed/rpm generates a lot
> of heat.
> 4. For a race car, the mentioned inertia upon gear changes is critical.
> Typically on a "mule drive" with reduced diameter fan, my experience
> indicates the belt problem occurs with two downshifts at the end of a high
> speed/rpm 4th gear straight.
> 5. IF, the race car is gently speed-shifted, the belt survives upshifts
> even at >7000 rpm. Assumes slick belt, properly adjusted with proper spring
> idler tension.
> 6. IMHO. YMMD.
>
> Chuck S
> BBRT
> ----- Original Message ----- From: <BobHelt at aol.com>
>
>
>  Jim,
>> Sorry I can't answer your questions, but I can tell you that according to
>> the test engineer's report on the Astro 1 engine, the horsepower to drive
>> the  fans was just about the same as required for the stock Corvair
>> engines.
>> I.e., about 27 hp at 6000 rpm engine speed. Of course belt life will be
>> much
>> better for the Astro setup. So we can see that the Astro 1's fans are no
>> more efficient than the Corvair's fans.
>> Regards,
>> Bob Helt
>>
>>
>> In a message dated 3/19/2013 7:22:20 A.M. US Mountain Standard Time,
>> simpsonj at verizon.net writes:
>>
>> the  cooling system was also radically different in that it used three
>> blowers
>> (squirrel cage?) on a single horizontal shaft.  The fan  routing was
>> simplified to eliminate the 90 degree bends and looks much more  like a
>> conventional  layout.
>>
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