All the reasons below are valid.
The reduced interference drag between the vertical and horizontal stab is
one of the key factors. Note that the surfaces are aerodynamically off
set
relative to each other, as well it provides an endplate for the vertical
stab.
I would venture to say if the conventional tail would give a 1/2 more
performance we would still see that type of tail. Never mind ground
clearance
and other disadvantages.




I have noticed that most if not all modern gliders are built with a
T-Tail (not sure about the term, I am talking about the elevator being
located at the top of the tailfin). While most power-aircraft I know
right up to the airliners have it at the bottom.

It gets the elevator/ horizontal stabilizer up into cleaner air with
fewer
flow blanking problems from the wing and fuze. Perhaps the biggest
advantage is
that it gets the stabilizer up high away from damaging obstructions. I
have
seen one low-down elevator get damaged in ground handling and it was not a
pretty sight.

Vaughn

What are the aerodynamic or constructive reasons for that?

Ciao, MM
--
Marian Aldenhvvel, Rosenhain 23, 53123 Bonn.
Fon +49 228 624013, Fax +49 228 624031.
http://www.marian-aldenhoevel.de
"I know you believe you understand what you think I said, but I'm
not sure you realize that what you heard is not what I meant."