Mailing List Message #41849
From: Bill Schertz <>
Subject: Fw: Duct Design
Date: Sun, 9 Mar 2008 09:22:33 -0500
To: Rotary motors in aircraft <>
Al Gietzen reported on his oil cooler performance. Here is some related cooling experiments performed by  friend of mine that solved his cooling problem
This is on an E-racer, using a supercharged IO-540. Lots of heat to get out. Standard scoops and NACA ducts were all tried, and adequate cooling could not be achieved.
He then went to armpit scoops, and it still didn't cool well, and pressure measurements indicated that pressure drop was occurring in the ducts, before they got to the plenum. Our speculation was that a 'burble' of air was forming in the curved duct, blocking the flow. He then inserted the divider shown in the photos, and the pressure in the plenum rose dramatically, and the cooling problem went away.
P3080071_s View into the duct showing divider
P3080074_s View from rear, You can see the divided channels.
P3080075_s View of the duct cover. This is an untested modification that he just recently made, to keep the flow separated all the way across the cylinders. One channel supplies air to the cylinder heads, and the other to the cylinder barrels. The system that worked (above) did not have the divider at this location.
P3080076_s view of the duct cover in place.
I don't know if this is the problem that Al is facing, but the symptoms are similar. Good pressure at the entrance to the duct, and not much at the face of the radiator (or in the engine plenum in this example.)
For what it is worth.
Bill Schertz
KIS Cruiser #4045
N343BS (reserved)
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