The basics of wing fillets
I've noticed recently a number of members who have posted questions regarding how to create nicely formed and blended wing fillets. Since I happened to be at that point in the construction of a Ziroli P-47 I thought I would shoot some pics and share what I know on the subject. The following steps show ONE way and certainly not the ONLY way to do this particular job. My hope is that there is some info here that everyone can glean from, no matter what procedure you prefer. Please note that I prefer to add the fillet AFTER glassing the wing and fuselage. This is because I use epoxy resin and micro balloons for shaping the fillet and it is much harder than raw balsa. If you try and blend it into an un-glassed fuse you will find the balsa sands much faster than the resin and blending the two together becomes an exercise in futility. Here's a list of the materials that you will need:
-epoxy or polyester finishing resin
-micro balloons (I prefer Sig)
-poster board or card stock
-sandpaper of various grits (I use 80, 100, 220, and 320)
-5 and or 30-minute epoxy
Step one is to create a properly shaped fillet base from thin plywood, I prefer 1/32. If you're working on a kit or from plans this may be established for you. If not, get out the trusty 3-view drawings and start scaling them up! The fillet base will attach to the wing saddle area of the fuselage so don't forget to extend it inside the fuse enough to have sufficient glue surface. Study the pic to get a better idea of what is needed.
Once you've created the ply fillet base the next step is to attach it to the wing saddle. I usually use 5 or 30-minute epoxy mixed with a bit of micro balloons to take up any gaps. You may want some time to adjust position of the fillet bases so don't be afraid to use the slower drying epoxy. Apply the glue to the wing saddle making sure not to get it anywhere that it can come into contact with the wing. Lay the saddles in place on the fuse and bolt the wing on, forcing the ply fillet bases into position. Take care not to let the fillet bases slide out of position and make sure both sides are symmetrical. If you have a particularly large gap between the saddle and wing it may be necessary to tape the plywood bases to the wing once everything is in position. The point is to force the bases down against the surface of the wing as tightly as possible and let the glue/micro balloons mixture take up any gaps between the base and saddle. Note, if there is anyplace where glue may squeeze out and come in contact with the wings' surface make sure to put some wax paper in place to prevent gluing the wing on! On the P-47 I left the aft portion of the fillet, that which glues to the side of the fuselage, loose for the time being. This part of the fillet is often easier to create from solid balsa (as we will see) and it may not be necessary to even have it as part of the plywood base. Every airplane and modeler is different so tackle this as you see fit.