Mike Wills wrote:

  Got my copy of Tracy's last newsletter yesterday and was surprised to
find a picture of my airplane in it. Things have changed some since that
picture was taken so thought I'd forward a couple of new ones. Hope these
files arent too big Paul.

Mike Wills

Nice work Mike. 

I think you need to skinny that duct down a bit near the back of
the rad. My test rig indicated you will get more flow through the back of the rad 
compared to the flow through the front of the rad with that shape of duct.
The ideal of course is even flow throughout the entire volume of the rad.

A quick fix is do what Tracy did with his oil cooler duct and stuff some porous foam
in the duct towards the back to slow the air back there. If it still cools 
then the opening is larger and has more drag than it need be or need have. 

You will of course not benefit  much from the slip stream velocity
with the opening so close to the hub of the prop. The slip stream velocity 
there is as slow as the aircraft forward velocity or slower due to external diffusion. 
The pressure in the duct of course is proportional to the square of the slip 
stream velocity. Particularly when climbing out, when cooling is needed the 
most, the slip stream velocity behind the outer half of the prop blade is much 
higher than the aircraft velocity. Are you still with me? Is that clear?

That is the reason I will move my opening down, sort of even with the bottom 
of the airplane, to take advantage of the higher velocity of the slip stream 
in that area.

Paul Lamar
 
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