Paul:
Not only do we have problems with cooling drag but it appears that we

need additional training on

computers.  Here are some pictures that we though went out yesterday.

Hope the size of the

pictures are OK and that they will help to tell our story.
Pete and Mark Rowe
RV 8    N108MR

Pete has a Lycoming (at the moment :-)) but he is doing some cowl pressure

cooling research which is

of intense interest to us.
Pete sent a lot of good pictures so I will handle just a few at a time.

OK what value of air pressure are you seeing here at what airspeed
in this NACA duct feeding the intercooler?

Paul Lamar

Paul:
The value of the air pressure at the intercooler is:
At 185MPH our manometer indicates 2.25 inches in the throat of the NACA
before the intercooler.
The manometer sensor positioned behind the intercooler indicates 1.2 inches
of pressure.

Mark and I noted that the air pressure measured on the opposite side of the
aircraft at the oil cooler turned out to be about the same.  The NACA ducts
are identical and we designed them from coordinates we found in Tony
Bingelis's book (Firewall Forward).

At 185 MPH our oil cooler manometer readings were 2.20 inches in the throat
of the NACA and 1.75 inches of pressure on the backside of the oil cooler.
Both the intercooler and oil cooler indicate roughly a drop of 1 inch across
the coils.  Is this good or bad?  Since the intercooler airstream
empties into the backside of the cowling and the oil cooler loops out
through a set of louvers we think the NACA's are working however we do not
know what the manometer should read on the backside of both heat exchangers?
Should the pressures read the same between the front and back of the
exchangers?
Pete

Good data. Thanks Pete. Just as I suspected. The dynamic pressure
at 185 MPH is 16.5 inches of water. You are only recovering about
13%. I am sorry to be the bearer of bad tidings but NACA ducts,
according to the guys that invented them, do not work well with
heat exchangers. The pressure in front of the exchanger is reflected out
into the opening convincing the air to bypass the opening. If you 
are going to effectively feed heat exchangers of any kind you are going to 
need a conventional duct. You can enlarge the opening on the front
of the cowl and feed some of the air to the intercooler. A good duct
for heat exchanger will recover 60 to 80% of dynamic pressure.
 
Paul Lamar
 
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