Why the T-Tail?

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

Quote: " 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?"

Yes. It's not pitch torque that is the issue. It is the torque on the
fin/fuselage junction about the glider's longitudinal axis, caused by
asymmetric and/or inertia forces of a tailplane mounted at the top of
the fin - maximum moment arm. That is much greater than from a
tailplane on or close to the fuselage level where its moment arm is much
less. I had a share in a T-tail glider where the fin/fuselage area
delaminated during a final glide with violent oscillations of the whole
empennage before the pilot reduced speed and landed safely.

Chris N.

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

"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

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

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.

What are the aerodynamic or constructive reasons for that?

Ciao, MM

It's nothing to do with aesthetics. It's just a happy coincidence
that aerodynamically efficient structures are beautiful things (and
not just for gliders).


Three reasons that may be significant are that:

1) The stabiliser is likely to be raised above the level of any crop
that the pilot may land in - therefore it will not be removed by
injudicious field-selection.

2) Also, I think I have read that a T-tail configuration produces one
less vortex than a conventional tail arrangement:- a vortex is spawned
from the end of each free tip of a tail surface (stabiliser or rudder)
therefore the top of the fin will not produce a vortex in a T-tail
arrangement (as the stabiliser prevents the fin from having a free
tip in the air stream). A vortex causes drag, therefore a T-tail will
be marginally more aerodynamically efficient.

3) Spin recovery is easier when the stabiliser is not in the
turbulence of a spinning main-plane - as is more likely to be the case
with a T-tail. Therefore a T-tail may be a safer aeroplane for
low-time pilots.



Jon.