Jerry Hey wrote:

I don't remember name of the person who mentioned the possible
availability of fail open thermostats but who ever you are I would
like to thank you.  I believe that the most precise control of engine
heat is with a thermostat but I worried about failure.   With the
fail open design,  thermostat failure is no big deal.  My engine
installation became simpler and lighter because movable cowl flaps
are no longer a part of the picture.  The other major simplification
was the addition of a  fan.  With the fan, I no longer need huge
inlets  associated with ground operations.  I can set  in line for an
hour at Oshkosh and remain as cool as a cucumber.    I am going to
size my inlets for a minimum air stream of 125 mph.     The Tailwind
will cross that threshold within seconds of closing the throttle.
Leveling off at 200 mph, I will flip the toggle switch that turns off
the fan.

  O.K.  this seems to be to good to be true. You are invited to shoot
me down.      Jerry

Good luck Jerry. Hope it all works. The best thermostat in the
world is not going to keep it cool if your cooling system is
inadequate. Actually any thermostat wide open is going to cut the
rate of coolant flow through the system. Power Sport is claiming 
that coolant flow rate is all important. 

Look at the temps people are running with rads in
the cowls and ducts in the front of the airplanes. It is easy
to get 80% dynamic pressure recovery if the opening is vertical 
right behind the prop yet people are still seeing temps around 
200F. If there is one thing we have learned in three and half years
it is the cooling system MUST be done right. 

As I recall those fans you have are 1800 cubic feet per minute. 
A 12" by 12" opening is one square foot and if you are doing 100 MPH or 
147 feet per second you have 147 cubic feet per second or 8800 cubic 
feet per minute of cooling air to work with in theory! 

A car going 70 MPH is losing about half the 40 HP it needs to get down 
the road to cooling or about 20 HP max. That is 15,000 watts at 
746 watts per HP. An airplane climbing out at 100 MPH is generating 
200 HP and about 100 HP is going out the cooling systems in terms of 
waste heat. That is 740,000 watts! Something to think about.

Paul Lamar
 
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