9-29-2020

Now that I am happy with the fabrication of the engine cowling it is time to decide on the types of fasteners I wanted to use (countersunk vs protruding) and proceed accordingly.

I decided (at least for the time being) that all fastners attaching the cowling to the airframe would be #8 protruding screws with all others being #4 solid rivets. 

On my lower cowls, common to the U channel, I have a 0.125" filler strap located between the skin and the U channel which I countersunk to accept the dimples in the cowling skin. However, along the upper cowl, common to the piano hinge, the hinge is too thin to use the same technique so I was able to dimple both the upper cowling skin and the piano hinge with no trouble. 

I found that dimpling both pieces together a the same time produced better results than I had when I tried to dimple them separately.

For the time being, after dimpling, these components are being held in place with #6 countersunk screws. Although these screws are not perfectly flush, they are flush enough to provide a flat surface that will allow me to form the cowling doors and obtain a tight fit.