To pick the angle you want, take a look at page 31 of this pdf, in the General efficiency section sticky:
http://me.dyu.edu.tw/lecture/Vehicle...ign%282%29.pdf
it is ~2mb and slow to load.
It shows that the ideal angle is different depending on how large the tail is. For a short tail (~1.5 ft), the ideal angle is roughly 13-14 degrees. For a *very* large tail, the angle goes up to 20+ degrees!
Food for thought.
Tom