Ageless Wings wrote:

Mornin', Andy

This is from the VeriEZ scoop.  I have the Veri and Long plans on the
Rutan CD in PDF format.

   Cheers,
    Andy

I have that CD, too!  Didn't even think of looking at the VariEze plans!  I
guess Burt switched to a prefab part before the Long EZ plans were
available.

Paul...

Now that we have some drawings for reference, I took the dimensions off of
my "prefabbed"  cowl.  Dimension 'A' on mine is 4.5" (the drawing calls for
4.6 inches), and the long axis of the ellipse on mine is 12.625".  The
drawing calls for 12.2".

Also, the radius of the lip on mine varies from 1 inch on the corners, to
1.1 inch measured at the long, straight sections. The plans call for 1.2".

The drawing's chart of dimensions only goes up to 100 horse engines (the
Continental O-200 engine for the VariEze ), whereas the later recommendation
for the Long was the Lyc O-235, which is around 108 hp, depending on flavor.

These dimensions do increase the cross section area of the inlet opening
somewhat, and may have been enlarged to try to make up for the 8 extra HP on
the larger recommended engine.

Harley

Give it 50 square inches roughly. .3 rule of thumb would be a core 
about 167 square inches or about 13 by 13. Sounds about right to me 
for about 100 HP.

One thing you got going for you in an air-cooled engine is the temp
difference between the fins and the air can be as much as 300 F. Since
the rate of heat transfer is proportional to the temp difference that
is far better than about 110 F you get with a liquid cooled system.
On the other hand the fin surface area of a rad can be far higher
than the fin surface area of an air-cooled engine. Back in WW II
P&W and CW machined the closely spaced thin fins on cylinders using a 
gang of cam controlled thin slitting saws. In general the fin surface
area of a rad is proportional to the volume of the rad.

BTW if the temp of the air is 60 degrees higher exiting the rad
than the air entering the rad the back part of the
rad is indeed working less than half as well as the front part of 
the rad. This is the reason for the rule of thumb that states the 
first half is doing three quarters of the work and why rads are 
getting thinner and thinner in cars.

The other factor is a thick rad is limited to the airflow it can pass 
at low speeds. Once you jam as much air in there as you can at a given 
speed more air will just refuse to flow through the rad regardless of
how large the opening. The air will merely decide to flow around
the opening. At that forward speed and below that forward speed you 
will get more air through a larger area thinner rad.
  
Paul Lamar
 
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