Why the T-Tail?

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.

John Giddy wrote:
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



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.
The one that tends to break them is the torque resulting from rapid translation
acceleration. With a T-tail the moment of inertia is far greater, so when you
ground loop, or perform a flick maneuver the lateral acceleration of the
elevator imposes large loads on the structure.

On Thu, 28 Oct 2004 08:07:07 +0200, Bruce Greeff wrote:

John Giddy wrote:
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



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.
The one that tends to break them is the torque resulting from rapid translation
acceleration. With a T-tail the moment of inertia is far greater, so when you
ground loop, or perform a flick maneuver the lateral acceleration of the
elevator imposes large loads on the structure.
Agreed, except that it is not just the elevator. It is the whole
tailplane.
Cheers, John G.

With a T-tail the moment of inertia is far greater, so when you
ground loop, or perform a flick maneuver the lateral acceleration of the
elevator imposes large loads on the structure.

Bruce,

I fully agree with you...the loads are highest in ground loops considering the
arm and accelerations. I haven't had the honor of doing a ground loop yet, but
just like landing gear up, the time will come.

Jim Vincent
N483SZ
illspam

Hi,

Thank you all, I have learned a lot. I have also come up
with two more things to consider, both rather minor I suspect:

- The control linkages are propably more complicated
in a T-Tail (con).
- With a T-Tail you can build the elevator in one piece so you
can rig and derig more easily (pro).

Now why are we not seeing more V-Tails? The main pro for T-Tails
seem to be:

- Good ground clearance
- Less drag
- Operates in clean undisturbed air

How does a V-Tail stand up against 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."

At 08:54 28 October 2004, Marian_Aldenhövel wrote:
Hi,

Thank you all, I have learned a lot. I have also come
up
with two more things to consider, both rather minor
I suspect:

- The control linkages are propably more complicated
in a T-Tail (con).
- With a T-Tail you can build the elevator in one
piece so you
can rig and derig more easily (pro).

Now why are we not seeing more V-Tails? The main pro
for T-Tails
seem to be:

- Good ground clearance
- Less drag
- Operates in clean undisturbed air

How does a V-Tail stand up against that?


Complicated mixing box required for elevator/rudder
control.

Marian Aldenhövel wrote:
- With a T-Tail you can build the elevator in one piece so you
can rig and derig more easily (pro).

This is also possible with a conventional tail, see e.g. the Libelle.

Cheers
-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!

Hi,

Thank you all, I have learned a lot. I have also come up
with two more things to consider, both rather minor I suspect:

- The control linkages are propably more complicated
in a T-Tail (con).
- With a T-Tail you can build the elevator in one piece so you
can rig and derig more easily (pro).

Now why are we not seeing more V-Tails? The main pro for T-Tails
seem to be:

- Good ground clearance
- Less drag
- Operates in clean undisturbed air

How does a V-Tail stand up against that?

Ground clearance is not an issue (I speak from experience)
It is questionable as to it having less drag. The theory says yes.
In practise it is not as easy to design a V tail that can match the T tail.
The lower part of the vertical stab on a T tail is in disturb air as well.
In case of the V tail you would have two surfaces in the disturb air.
The mixer is a simple and light weight mechanical device. If built and
installed right cross interference is minimal.

Udo

Earlier, Peter Wyld wrote:

Complicated mixing box required for
elevator/rudder control.

I don't think that such devices are necessarily complicated. Dick
Schreder designed a variety of mixers for the HP/RS-series sailplanes,
including cats-cradles and arm-on-arm systems, and none of them were
particularly hard to build or maintain. You can view the drawings for
the HP-18 ruddervator mixer he

http://www.soaridaho.com/Schreder/Sc...76_Page_36.jpg

An aft-looking-forward drawing of the HP-18 ruddervator mixer is at
the bottom of that page. Sure, it's more complicated than a direct
connection to an elevator. But compared with some other glider
mechanisms, for instance the flap mixer in the ASW-20 or the gear
retract system on the original Twin Astir, it's relatively simple and
straightforward. Also, it transmits rudder as well as elevator inputs,
so some of its complication results in eliminating a separate rudder
circuit. So, in terms of overall aircraft control system complexity,
it comes out only slightly worse than more conventional
rudder/elevator systems.

Probably the best thing about V-tails is that with them you have one
less tail surface to construct, finish, paint, and mount. You have
fewer hinges, and fewer intersections. You leave more stuff on the
ground, and get more use out of what you do take into the air.

However, as I develop the next-generation HP kit sailplane, I've had
to make the unhappy decision to go with a T-tail. The primary reason
is aesthetics: My surveys suggest that I can substantially widen my
tiny market by offering a low-cost go-like-stink glider that looks
just like all the other go-like-stink gliders. Secondary reasons
include that, in composites, I found it easier to develop mounting
provisions for a conventional T-tail horizontal surface than for an
equivalently-sized set of diagonal surfaces. Other reasons include the
convenience of decoupling the sizing, deflections, and mass-balancing
of separate rudder and elevator surfaces, and the greater ease of
developing and installing control circuits in the aft fuselage.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24
*fuselage shell molds complete, readying wing and tail tooling*

This is the only fatality I am aware of at Avenal, and the
only ruddervator mechanism-related T-tail fatality I have read.

NTSB Identification: LAX92LA393 .
The docket is stored on NTSB microfiche number 48074.
14 CFR Part 91: General Aviation
Accident occurred Friday, September 18, 1992 in AVENAL, CA
Probable Cause Approval Date: 9/14/1993
Aircraft: SPARKS-SCHREDER HP-140V, registration: N704B
Injuries: 1 Fatal.

Prob cause:
" THE LOSS OF PITCH AND YAW CONTROL DUE TO THE SEPARATION OF THE
RUDDERVATOR CONTROL CABLE FROM ITS CLEVIS FORK DUE TO IMPROPER INSTALLATION."

In article ,
Peter Wyld wrote:
At 08:54 28 October 2004, Marian_Aldenhövel wrote:
Hi,

Thank you all, I have learned a lot. I have also come
up
with two more things to consider, both rather minor
I suspect:

- The control linkages are propably more complicated
in a T-Tail (con).
- With a T-Tail you can build the elevator in one
piece so you
can rig and derig more easily (pro).

Now why are we not seeing more V-Tails? The main pro
for T-Tails
seem to be:

- Good ground clearance
- Less drag
- Operates in clean undisturbed air

How does a V-Tail stand up against that?


Complicated mixing box required for elevator/rudder
control.




--

------------+
Mark J. Boyd