Some of these things really are a labour of love, my fingers are quite sore from all the sanding, I have to admit I am glad this is done. I sprayed the duct black before I installed it so that I would have a visual indicator of when I had sanded through the bog and hit the actual fiber glass, my main concern was that I would sand through it.
After lots of sanding I have a nice smooth transition between the cowl and the NACA duct
