Why the T-Tail?

Hi,

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.

What are the aerodynamic or constructive reasons for that?

Ciao, MM
--
Marian Aldenhövel, 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."

"Marian Aldenhövel" wrote in message
...
Hi,

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 Aldenhövel, 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."

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."

Pro T-tail: It's in the clean air.
Contra T-tail: Huge torque forces.

The torque forces are more easily mastered when the planes are small.
There are biz jets and turboprops with T-tails. On the other hand, all
serious acro planes, gliders included, have "conventional" tails.

Stefan

Stefan wrote:
Contra T-tail: Huge torque forces.

I know what force is and what torque is, but what's ``torque force''?
I see no significant difference in the pitch torque generated by a T
tail and a conventional tail (apart from a minimally longer arm for a T
tail on a given typical glider design).

Am I missing something?

-Gerhard
--
Gerhard Wesp o o Tel.: +41 (0) 43 5347636
Bachtobelstrasse 56 | http://www.cosy.sbg.ac.at/~gwesp/
CH-8045 Zuerich \_/ See homepage for email address!

I know what force is and what torque is, but what's ``torque force''?
I see no significant difference in the pitch torque generated by a T
tail and a conventional tail (apart from a minimally longer arm for a T
tail on a given typical glider design).

Am I missing something?

The torque is around the rolling axis, not the pitch axis.

With a conventional tail, the rolling torque is based on the distance from the
fuselage center line to the CG of the elevator surface. In a T-tail, the
distance is based on the whole length of the vertical fin, so the moment arm is
greater. Hence, greater torque force.

Jim Vincent
N483SZ
illspam

"Jim Vincent" wrote in message
...
I know what force is and what torque is, but what's ``torque force''?
I see no significant difference in the pitch torque generated by a T
tail and a conventional tail (apart from a minimally longer arm for a T
tail on a given typical glider design).

Am I missing something?

The torque is around the rolling axis, not the pitch axis.

With a conventional tail, the rolling torque is based on the distance from
the
fuselage center line to the CG of the elevator surface. In a T-tail, the
distance is based on the whole length of the vertical fin, so the moment
arm is
greater. Hence, greater torque force.

Jim Vincent

Ever watch a Zuni tail during take off? I gather it's also interesting to
watch in flight, but Zuni drivers don't really like using mirrors;^)

Frank Whiteley

Gerhard Wesp wrote:

I know what force is and what torque is, but what's ``torque force''?

It's me being sloppy in the usage of a language which isn't my first one.

Stefan

It's me being sloppy in the usage of a language which isn't my first one.

Stefan


Stefan, if you use that excuse, that leaves those of us for whom English is
the first language with no excuses for when we're sloppy;-)

Jim Vincent
N483SZ
illspam

It's me being sloppy in the usage of a language which isn't my first one.



Actually, it is me being sloppy.

Torque is really the moment arm times the force (R X F). The force is the same
since the elevator is merely translated from one position to another. The
moment arm increases from the base of the fin to the top of the fin. So it is
the torque that increased, not the "force" per se.

Then again, with a T-tail, the elevator is no longer essentially in rotation,
but also in translation, so there that to consider too...

Jim Vincent
N483SZ
illspam