Why the T-Tail?

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

On 27 Oct 2004 15:30:43 GMT, Jim Vincent wrote:

snip
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

Jim,
Why does the elevator have more translation on a T-Tail than on a
conventional one please ? (I presume you are referring to translation
in a direction normal to the tailplane surface)
Bemused John G.

Jim,
Why does the elevator have more translation on a T-Tail than on a
conventional one please ? (I presume you are referring to translation
in a direction normal to the tailplane surface)
Bemused John G.

John,

If the stab is mounted at the fuselage, if there is roll, the stab only
experiences a rotation around the center of the stab.

If the stab is T, then not only is it rotating, it is also moving in a circle
with a diameter of the rudder fin. Does that make sense?

Also, with a T, if you go full rudder in one direction then another, the fin
adds the inertia of the stab mounted at the top of the rudder...a torsion from
yaw too!



Jim Vincent
N483SZ
illspam

On 28 Oct 2004 02:44:06 GMT, Jim Vincent wrote:

Jim,
Why does the elevator have more translation on a T-Tail than on a
conventional one please ? (I presume you are referring to translation
in a direction normal to the tailplane surface)
Bemused John G.

John,

If the stab is mounted at the fuselage, if there is roll, the stab only
experiences a rotation around the center of the stab.

If the stab is T, then not only is it rotating, it is also moving in a circle
with a diameter of the rudder fin. Does that make sense?

Also, with a T, if you go full rudder in one direction then another, the fin
adds the inertia of the stab mounted at the top of the rudder...a torsion from
yaw too!



Jim Vincent
N483SZ
illspam

OK Jim,
I agree. I was thinking of normal elevator operation, and movement in
the pitch direction, which is the same for both arrangements.
Cheers, John G.