<VV> Electric cooling fan results

[Rad Davis]

That's a terrible oversimiplifcation of how aircraft engine cooling works.

The prop wash generally does a very poor job cooling the engine.  It's quite
possible to overheat most air-cooled airplane engines by running at full throttle
on the ground for an extended period of time.

What cools the engine is ram air from the motion of the airplane.  Low and slow 
corvair-powered airplanes (cruise in the 50-80 MPH range) do well with this with
a modestly-designed cooling system, the faster airplanes generally have even less
trouble with engine cooling as long as the ductwork is properly laid out.

The problem you have with cooling an engine in a car is that the car tends to spend
a fair amount of its time sitting still while running, and it may be heat-soaked
from a high speed run immediately before.  The fact that the air being blown over
the engine is at the ambient temperature four feet above the pavement doesn't
help either.

Somebody (I think Warren Leveque) said that ram-air cooling of the corvair engine
works fine as long as the car is going forward at about 30 MPH or faster. Dryer 
hose was used from the headlight buckets to the tops of the cylinder heads as the
ram air source.

I've wanted to try an eddy-current clutch system with a variable-current controller
for years.  That would give the option of infinitely-variable fan speed relative
to engine speed, but still standard belt drive.  Tatra used thermostatically controlled
fluid clutches on some of their big diesels.  That might also be an option.  Likewise,
any fan improvements would only help.

But the electric fan tests underlined what was said here years ago: 

http://www.mindspring.com/~corvair/RadFAQ/ElectricFans.html

Moving air at x CFM is easy.  Moving it at x CFM at a significant pressure head 
requires a significant amount of work to compress the air.  And work = power
requirement no matter how you supply the power.



-----Original Message-----
>From: wblanning at comcast.net
>Sent: Jul 29, 2007 6:42 PM
>To: Virtual Vairs <virtualvairs at corvair.org>
>Subject: Re: <VV> Electric cooling fan results
>
>Maybe the experts can clarify something about re the fan discussion.  I understand
that Corvair powered aircraft have no fan, but use the propeller wash and/or air
speed to force air over the engine.  So if Corvairs had their engines in the front
where air would be forced over the engine by the car's forward motion, would
an electric fan suffice for low speed driving needs?  Is this the theory of other
front engined cars?  (Not that I plan to change my Corvairs engine location of course).
>
>Wade