The Question has been raised many times as to how to make the fin fillet
that is common of many of the fabric covered Piper Airplanes. Rather
then go into it in detail here, I'll simply add the  link to the L-4 Grasshopper
Page on the E-Zone that explains it in full detail. Clink the link below for
the full story:

http://www.rcgroups.com/forums/showthread.php?t=833111&page=7