<VV> Electric Fan - An Engineering Approach to What is Gained andLost

[Ron]

It's just the nuisance of trailering your electrically cooled Corvair over 
every decent hill.
RonH

----- Original Message ----- 
From: "boB" <bobquincy at mindspring.com>
To: <fastvair at yahoogroups.com>
Cc: <virtualvairs at corvair.org>
Sent: Friday, August 12, 2005 6:54 AM
Subject: <VV> Electric Fan - An Engineering Approach to What is Gained 
andLost


> So why are Corvair owners chasing the elusive electric fan?  What is the 
> point?
>
> To me the point of an electric/hydraulic/anything-but-belt-driven fan is 
> not fuel economy, nor belt flipping, nor even improved cooling, but *more 
> available HP* right when we want it the most, at high rpm.
>
> Anyone who runs at high rpm isn't concerned about fuel economy anyway, 
> plus I never had belt problems once I got things sorted out on my '66 
> Monza, even up to 7000 rpm.  But I sure could have used more available HP!
>
> By decoupling fan speed from engine speed we can maintain cooling *and* 
> get more power to the wheels.  If the new fan provides the same *average* 
> airflow over time as the original fan we should see the same average 
> cylinder head temperature.  Yes, there will be temperature spikes but if 
> they are very short in duration then the thermal mass of the engine should 
> keep the temperature regulated well enough so no overheating is seen. 
> Kinda' like making a drag strip pass without the fan belt on, on the 
> street it's difficult to use full power for more than 15 seconds without 
> losing your license.
>
> An electric fan runs at a constant speed and will provide sufficient 
> cooling at some load, more cooling than the engine needs at lighter load, 
> less cooling than the engine needs at any greater load.  For most street 
> engines that midpoint load is probably a steady cruise of about 75 mph. 
> Of course this depends on where you drive; temperature, hills, traffic, 
> speed limits are all factors.  I often drive I-95 to Florida, high 
> temperatures, sustained speeds near 80, no hills to speak of.  My fan 
> would be different from someone's who lives in the Rocky Mountains, and 
> when I visit there I would have to carefully monitor head temperature and 
> probably change my driving style to keep the engine from overheating.
>
> The electric fan runs primarily from alternator power.  With an efficiency 
> of about 80% for the alternator, and another 80% for the fan motor we get 
> an overall energy transformation efficiency of about 64% *so* the belt 
> driven fan is much more energy efficient from that approach.  Where the 
> electric fan excels is when we can freewheel the alternator at high engine 
> speeds and run the fan from the battery, freeing up available HP.  The 
> battery charge/discharge efficiency reduces our overall efficiency maybe 
> another 80% but this power comes from the average HP over all engine 
> speeds, especially when we don't need more HP as in steady cruising or 
> even deceleration.  But with all of these energy conversion losses don't 
> expect any fuel economy gains.
>
> This approach is not far different from that of a hybrid vehicle, use a 
> small engine for cruising, assisted by batteries for peak demands.  In 
> this case we're using engine power to provide average cooling, and the 
> battery to provide cooling for peak demands.
>
> Obviously this approach would require a much larger fan for racing than 
> for street driving, where the race engine is putting out maximum power for 
> most of the lap.  It's entirely possible that a large enough electric fan 
> to keep a racing engine cool doesn't exist, at some point it is clear that 
> the electric fan will *not* be able to keep up with the engine's cooling 
> demands.  But for *some* applications the electric fan *will* provide 
> enough airflow to keep the engine as cool as the original fan, with the 
> added benefit of more available HP.  And for some Corvair owners that's 
> worthwhile.
>
> The question is: how well does your application fit the available 
> airflow?!
>
>
> boB
>
>
>
>
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