I'm going to dig this up in the hopes I can get some input and help.

I'm currently converting my ARF Senior Telemaster to a V tail. I have removed the stock stab in one piece and used one of the ribs as a template for my new stab. I scatch built two halfs with the same cord and length as the stock horizontal stab at 17". Today at the field a guy warned me that my surfaces may not be big enough and that was confirmed by BMathews via a PM. I have the ability to extened each side about another 3 inches which is roughly 20% more surface.

Now I consider myself a smart guy but I can't figure out the actual formula.

Any help or advise would be great.