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

[Jim Simpson]

I stand corrected -- the fans on the Astro 1 look to be pretty large in
diameter; closer to the stock fan than I had thought.  I'll have to scale
them from the drawings posted to see and then run a rough calculation to be
sure.  But I'd still like to go through that design to see what the tradeoffs
might be.  Perhaps trading a bit more inertia for a simpler belt drive, better
cooling and easy to engineer overrun clutch?

Jim Simpson

On Tue, Mar 19, 2013 at 2:09 PM, Jim Simpson <simpsonj at verizon.net> wrote:

> 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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>>
>