Why the T-Tail?

In article ,
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?

The V-Tail setup is less likely to cause fuse damage in a ground loop.

Regards,

-Doug

illspam (Jim Vincent) writes:

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!


Was the Airbus that broke up over NY in 2001, according to the just released
NTSB report, from "Improper use of the rudder", a T tail?

Steve

Doug Hoffman wrote:
In article ,
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?


The V-Tail setup is less likely to cause fuse damage in a ground loop.

Couldn't the T-tail designer just make the fuselage stronger? Or the
V-tail designer make the fuselage lighter to take more advantage of the
lower tail CG, so they both withstand a ground loop just as well?

Maybe JJ or some other glider repairer can tell us how tail booms
commonly fail - torsion or bending, and if there seems to be a
difference in types of failure between the tail types.


--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Actually Steve, it was a V Tail ;-)

Was the Airbus that broke up over NY in 2001, according to the just released
NTSB report, from "Improper use of the rudder", a T tail?

Steve




Jim Vincent
N483SZ
illspam

The designer could make the fuselage so strong that it would never break, no
matter how fast the ground loop of snap roll. But then the fuselage would be
twice the area, four times the weight, and the glider would never get off the
ground.It is all a trade off in strength to performance.

It is not a given that the tail will break in a ground loop. Most gliders are
designed to survive ground loops with no damange, 'cept maybe a dizzy pilot.

Couldn't the T-tail designer just make the fuselage stronger? Or the
V-tail designer make the fuselage lighter to take more advantage of the
lower tail CG, so they both withstand a ground loop just as well?



Jim Vincent
N483SZ
illspam

"Eric Greenwell" wrote in message
...
Doug Hoffman wrote:
In article ,
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?


The V-Tail setup is less likely to cause fuse damage in a ground loop.

Couldn't the T-tail designer just make the fuselage stronger? Or the
V-tail designer make the fuselage lighter to take more advantage of the
lower tail CG, so they both withstand a ground loop just as well?

Maybe JJ or some other glider repairer can tell us how tail booms
commonly fail - torsion or bending, and if there seems to be a
difference in types of failure between the tail types.

Lotsa Libelle booms have been broken, but then the shape may have something
to do with that, or just the sheer numbers of Libelles built skews the
sample.

Several PIK-20 tail booms have unzipped along the lower fuselage seam from
ground loops. No idea how that compares to those that actually broke the
boom. From what I've heard, once repaired, they don't unzip again.

What about those booms that break in two places? Peculiar to make, or type
of accident?

Frank Whiteley

Mis-rigging could happen to any type. A school teacher was killed in Wales
one day while I was soaring due to mis-rigging one of the ruddervator
control guides on his v-tailed BG-135, diving in from the top of the winch
launch (his second of the day). It was only the second occasion he'd rigged
the glider IIRC. Could have been a t-tail.

I flew a v-tailed SHK for four years. The rigging of the control guides was
very similar and held the same potential for being mis-rigged as the
aforementioned BG-135. The sad part is that the guide is clearly in view
during control deflection. This is one very specific instance where a PCC
might not have detected the problem, but a visual inspection would. The
fact that he made the first flight successfully attests to this. The actual
disconnect probably happened during ground handling or during he landing
role and wasn't noticed before the second flight.

Frank Whiteley

"Mark James Boyd" wrote in message
news:41818446$1@darkstar...
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

John Giddy wrote:
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.
I stand corrected - Cirrus drivers sometimes forget that there are sailplanes
that have fixed horisontal stabilisers... ;-)

(JonB) wrote in message om...
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

To insure that your boom will snap during a groundloop, thereby
keeping our glass repair shops in buisness. (mass at the end of the
moment arm)
Seriously, I believe spin recovery and crop clearance to be the
primary reasons.
Why not a "V"? Ever flown a Bonanza in rough air? V's have a yaw-pitch
coupling that I find annoying.

-Dan

On Fri, 29 Oct 2004 08:23:18 +0200, Bruce Greeff wrote:

John Giddy wrote:
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.
I stand corrected - Cirrus drivers sometimes forget that there are sailplanes
that have fixed horisontal stabilisers... ;-)

That thought had crossed my mind, but I resisted the chance to point
it out :-)
Cheers, John G. (Std Cirrus Ser: 6720