I've searched various forums, read some articles and books and drawn some general conclusions concerning V-Tails - There seems to be two opposing "universal truths" concerning their use:
1. V-tails don't work very well. Despite their theoretical aerodynamic and structural efficiency, if the Bonanza and Sonex/Waiex series has shown us anything, V tails turn out heavier, more complex, less stable, and without any speed advantage.
2. UAV's frequently feature V tails. Vehicles used for long endurance intelligence, surveillance, and reconnaissance (ISR) missions need all the efficiency they can get, so the theoretical advantage of V tails is a logical (and popular) choice.
My question is this: If V tails generally are a poor choice for light aircraft, then why does this design feature show up on so many UAV's large and small?