An interesting thread on V-tails, but it seems a little short on the actual design theory.  What this set of formulas and relationships does is to provide a guide for converting a conventional tail to an equivelent V-tail.  While I originally researched it for use in RC pylon, where everyone just copied from other designs and the first guy just used what glider guiders used.  The flatest I've flown was 130 degrees which had great performance in the air, but failed to give any ability to alter course on landing where you need to miss other airplanes, so I ended up at 120 degrees.  The angle on a Beech Bonnaza is 118 degrees, BTW.
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Measure the areas of the original design's vertical and hoizontal surfaces.

A lot of sport models use about 1/3 of the horizontal area for the vertical area. To figure the angle the following example shows the basic math for such a ratio.

Once the ratio of vertical to horizontal surface area is determined, it becomes a simple math problem to calculate the angle of the V, as well as the area.

The basic trigonometric function is : Sin^2  + Cos^2  = 1

{This should read Sine squared Theta + Cosine squared Theta equals one}

If we want the ratio to be 1:3, then Theta () needs to result in:
0.25 + 0.75 =1

The square root of 0.25 is 0.5, and the square root of 0.75 is .866

The arc-sine or inverse of the sine function of 0.5 gives 30 degrees.
The arc-cosine or inverse of the cosine function of .866 also gives 30 degrees.

Thus, for an equivalent ratio of 1:3 for the vertical to horizontal area, the angle of each half of the V-tail need to be 30 degrees above the horizontal plane. Since the angle between the V is typically called out, it becomes 120 degrees (180 – 2(30)).

There is some disagreement as to the area required. They range from:
a) using the same size as the existing horizontal stab area
b) using the projected stab area of the V the same as original
c) using the same total area as the combined area of the original tail
d) using the square root of the sum of the squares of areas of the vertical and horizontal

Gliders often use very acute angles (90-110 degrees), because they need a lot of rudder authority.
Pylon racers often use (110-120), I’ll reserve comment as to why.

A few years ago, in doing my best Adamisin act,  I took my airplane design of that time, Blue Moon, and took the flat stab and set it up in a 30 degree lift into a V tail on each side and called it Midnight Lace to go with the lace paint job.  I found no need to alter areas from the 23 percent I had on the flat tails. What WAS different was the huge handle bias needed to get turns equal both ways.  Once there I could perceive no flying differences in good air. I got many favorable comments on the ship but its downfall was in turbulent air the tail couldn't decide whether to be stab or rudder.  Even did a half barrel roll and back once at a Topeka contest on one of those crazy days at the OLD field.  If not for that I might be flying a V now.

Dave

3/9/13...way old thread I know but I just found an old photo of the above mentioned airplanes about '95-6.  Picture of a picture so sorry if it's not too good.

My dad's profile V-tail Bonanza powered by a ST .40 flies great for a fun sport plane.

I would sort of think that a properly set up V-tail would be very similar to the infamous "wiggle" rudder.