Hi Thurman,

I would suggest you have a play with Curtis Suter's 'SailplaneCalc' excel file. It's designed as a tool for sizing the tail for sailplanes and for converting from conventional tails to V-tails. It's obviously not intended for P30 but does exactly the same job on any model, taking the dimensions and doing the maths for you.

There is a quick converter file which will work if your tails are mounted the same distance from the wing. If the fin is significantly ahead of or behind the tailplane then I'd suggest you put in the dimensions of your model into the full version of 'SailplaneCalc Cruciform Tail' to find the Vertical and Horizontal Tail Volumes (Vh and Vv) of you current P30. Then play around with the areas and angle of in 'SailplaneCalc V-Tail' until you get the same numbers with a V version.

Rubber duration models have very large horizontal tail volume (Vh) and modest vertical tail volume (Vv). this means that the V-tail will probably come out a bit flatter than the 120 degree included angle as the tail needs to do much more work in the pitch axis and less in the yaw axis.

The projected area method leads to rather less area than you actually need. The finished V-tail should have the same total area as the original tailplane

**plus** the fin area. If you think about it the V version is now working to give the same pitching force as the tailplane was but now also has to provide the neccessary yawing forces at the same time. So it needs a bit more area than just the projection.

The excel files can be found here:

http://tailwindgliders.com/Files.htmlUsing your numbers in the converter I get

Current Tailplane area: 32.5in2

Fin area: 9in2

New V-Tail area: 20.75in2 each side

V tail dihedral angle: 27.8 degrees (included angle 124.5 degrees)

Jon