Wing Root Fairings
My ideas for the wing root fairing were based in the successes with large wing root fairings a friend had with his Hummelbird as well as Kent Paser's successes outlined in his book "Speed with Economy". After delving into some of the NACA research of the late 1920s and 1930s, I failed to come up with any formula for the size of the fairings beyond simply building it as a ratio of fairing size to wing root size as shown in some of the testing listed in a ASE report.
I considered various methods to build the wing root fairing, but finally settled on building a bottom with 1/4" clark foam to stiffen it at the bottom and over top of the flap. The design goal is to make the flap retract cleanly into the bottom of the fairing. The bottom piece is standard "kr glass" laid up flat on a waxed formica bench top with the foam attached via a slurry of micro balloons. It was trimmed to overlap the bottom of the fuselage, then bent up over top of the flap. The jacks in this photo are holding a piece of 1x2 that is covered with plasticholding the glass layup tight against the bottom of the plane while the epoxy cures.
The top piece is two layups of glass laid flat on the same waxed formica workbench. It was bowed and floxed into place. To hold it while the flox is curing, there are screws into the top of the old wing skin and waxed staples shot into the side of the fuselage and through the outboard trailing edge into a piece of plastic covered 1x2.
With all the fasteners gone and staples pulled, here is the end result. The excess flox you see is actually on the inside of the lay up and is excess weight that could have been eliminated by doing a neater job.