Mailing List Message #33328
From: Ernest Christley <>
Subject: Building exit duct
Date: Wed, 23 Aug 2006 13:35:14 -0400
To: Rotary motors in aircraft <>
My exit duct will be on the top of the wing, just aft of the maximum thickness.  The airplane sits on the ground with approximately 9 degrees of nose up angle, so  I wanted a design that make rain water/leaves/other debris run off the back rather than down into the duct.

I started by building up a form around the fiberglass wheel well that was even with the top skin, and then glassed it all around, leaving the top open.  Then I made up some foam 'sticks', covered in packing tape, each about an inch wide.  Both sides and the back are tapered.  I lay on one at time, covering it with 2" tape.  The next stick would lay on top of the excess tape from the previous. There are 6 sticks, each 9" wide and 1/2" high, for about 27"^2 of exit area.  Each intake is a little more than 4"x6", for about 25"^2 intake area.  Not the optimum ratio, but I expect to have excellent pressure recovery (full length K&W ducts), low losses (large, mostly straight, interim duct area), and a somewhat negative pressure on the exit area (due to the location on the airfoil).  If I need more exit area, I have the option of opening the rear of the exit duct and fair it into the top skin without much effort.  If I have too much cooling, I have the option of first removing the scoops from the intake, and then closing up one or more of the exit holes.
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