It's important to note that the V tail angle is not related to any "Golden" angle but rather it's only function is to distribute the horizontal and vertical area in a ratio similar to what exists on a conventional model. The fact is that we NEED more horizontal than vertical area in most cases and that is the only reason the angle is more open than 90. Mark Drela and Don Stackhouse (at DJ Aerotech) have gone to great lengths to show that you need to look into the whole thing more than just looking at the conventional flat areas and transforming them into projected areas of the V tail. The angle required in the end has a lot to do with the ratio between the required vertical and horizontal tail volume coefficients. I think that if the final angle comes out as being in a fairly narrow range of angles then that is more good luck than good planning. There's GOBS of stuff written to Don at his site about Vtails and he make reference to some of the material that he worked from as well in his answers...

http://www.djaerotech.com/dj_askjd/

FH, I think what you have with your rule of thumb is a system that will work great as long as you're not trying to cut the areas really fine to the bone like with some slope racers or F3B models where the designers try to cut the tail areas to the minimum to limit the drag. At that point I think it would be important to do the math and use what the numbers say. But for someone trying to mod a Gentle Lady or Spectra it sounds fine.

A couple of more items....

The bit about the upward elevators acting like a drag brake is more related to the angle of throw. I have heard that the up elevator on a V tail often has more authourity than the down elevator because the often used clearance V closes and contains the air better with each surface acting like an end plate for the other. The effect does not working with the same strength when the angle opens during down elevator. I believe this last bit was on the DJ Aerotech site in the same questions area. FH, I suspect you were using the same angles for up and down. If you had tuned the angles such that the inside and outside looping was the same radius perhaps the up elevator angle would have been less and the braking effect reduced.

FH, you also said....
I think you got spirally unstable and dutch rolling confused in that bit. Dutch roll comes from too small a vertical area which. Too much area in the vertical shows up as a model that is spirally unstable.

Rico, CA and debonder may work or what about trying Ambroid or Sigment with light fiberglass reinforcing? If you do this I suggest the Ambroid as it's thinner and will soak into the surface's end grain better. Double glue the area by coating the boom with a thin layer and force some into the end grain of the surfaces and coat the butt ends for about 3/8 to 1/2 inch out on the outer surfaces. After it dries glue the surfaces on with a second coat of wet glue and let dry. Then reinforce the joints with some 3/4 wide strips of glass or carbon cloth using more Ambroid as the "resin" You may need two or three coats to fill the weave. Once it dries completley for a couple of days it'll be super strong but if you want to soften it to move things you can just lay acetone or dope thinner on the Ambroid until it sofens and either bend it into the new angle if the change is minor or keep softening the glue until it releases all the way so you can install new surfaces or radically modify the angle if needed. Sigment works the same way but it comes out of the tube quite a bit thicker. For this use I'd thin it with some acetone to a thick brushing consistency instead of the jelly like thickness that is stock. Otherwise it tends to dry too fast and ball up as you are trying to spread it.