Chapter 23: Cowl Closeouts
(....a very long Step 3 continued)
Cowl Closeouts
To prepare for the 5-BID closeout layups, I bondoed a board across the aft edge of the top cowl. The aft edge was pretty wavy without it. The plans have you bondo some sticks across the seams to hold the cowls together while you glass in the 5-BID layups. Hmmm, I'm not entirely sure I can do that with the AeroCad cowls since "the seam" is formed in the lower, aft corner. So I'm assuming the AeroCad cowls are different from the Featherlite cowls. To stabilize the cowls even further, I used clecos to hold the aft edges together, then used duct tape to hold the aft-most seams together for glassing. You can see the sort-of finished product in the picture on the right. I say "sort of", because if you look closely, you can see the edge of the lower cowl sticking out way right of "the seam". I'm guessing AeroCad left some extra material there so you could trim and cosmetically match the cowls.
NACA Scoop
The hardest part of making the cowl lip for the NACA scoop was doing all this work while under the plane. It would be easier if the plane were upside down, but progress is progress. The first picture is of the big block of urethane foam shoved up in the NACA scoop, carved to shape, with the 4-BID layup applied. The next pictures show the completed NACA flange after removing most of the foam, carving the airfoil shape, and glassing 2-BID over that . (Don't forget to overlap onto the 4-BID layup.) On the 2-BID layup, it definitely helped to first make up a paper pattern that perfectly fits the NACA flange, then transferring the pattern onto the layups (between two plastic sheets), and cutting the glass layups to match.
I later added some vortex retainers to the NACA scoop. Oil flow tests by Marc Borom showed that air was spilling out at the corners of the scoop, thus disturbing laminar flow and cooling effectiveness. The retainers capture the vortices and guide the incoming air into the scoop. Marc's CHTs were lowered about 30 degrees. To make the retainers, I just took small pieces of foam shaped into triangles, then 5-minute glued the triangles into place on the NACA scoop and lip. I shaped the foam, then glassed over them with 2-BID. These would have been easier to make had I built them when I was making the cowl lip.
