N247BR

Engine Cowling - Air Inlet 

The original plan for the cowling air inlet was to use the supplied NACA duct.  I installed the NACA inlet before I realized that the throttle body and filter box would NOT fit within the lower cowling.  The entire underside of the cowling needed to be lowered and the NACA inlet was too far back.  I was forced to redesign the entire air inlet.  In addition, the air filter was offset from the center line by a full inch.  I also wanted to find a way to support the lower cowling when mounting.
The air box and inlet form is described in another section but the inside inlet is shown inserted into the airbox.	This page shows the process of construction for the external cowling air inlet.
The process starts with installing the fiberglass airbox inlet which will be the inside of the cowling air inlet.  Foam was then used to surround the internal inlet and start filling in the opening.  I used two different foam types because it was the only thing I had available and they were not intended for permanent use.  The foam is nothing but a mold for shaping and application of glass overlay.  The idea is simple, fill everything with foam, remove foam until you get the desired shape.
The underside of the cowling was extended forward with a glass panel and attached to the existing panel.  I used a rasp and various grits of sandpaper to shape the foam.
The shaping process continues with the application of an epoxy micro mix used to fill the pores of the foam and fill any low spots.  It's mostly a trial and error process that repeatedly adds some filler and takes some away.  A lot of time is spent examining the results both close up and from a distance.  I didn't like the initial look and made substantial changes to soften the appearance.
The initial opening was too extended and did not blend in smoothly.  The opening was not rounded out enough.  I had to rework it several times.
Once I was finally happy with the basic shape of the inlet and cowling I added multiple layers of glass over the foam form and micro filler.  I sanded the micro with 80 grit before application of the glass.  After the glass was applied and cured, it was sanded and the light weight filler (blue) was added and sanded until everything was smooth and no edges from the glass overlay.
At this point I continued to work on the hinge line between the upper and lower cowling, the air vents, and the nose.
It would have been so much easier if I had just kept with the KISS idea and not changed anything.
All the major work has now been done and it's time to start the finish and painting work.