Why the T-Tail?

[Marian Aldenhövel]

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."

[Vaughn]

"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."

[Stefan]

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

[Udo Rumpf]

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."
>
>

[Andreas Maurer]

On Tue, 26 Oct 2004 11:46:18 +0200, Marian Aldenhövel
> wrote:


>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?

A T-Tail has significantly less interference drag
(Interferenzwiderstand) than a conventional one. Since its weight is
located on top of the vertical stabilizer (Seitenflosse), fuselage
structure needs to be stronger, but the additional weight is
acceptable for a glider that needs to have as little drag as possible.


Bye
Andreas

[Super Friendly Aviator]

The 'T' configuration gets the tail out of the way
of crops when field landing and consequently helps
to be prevent it from being ripped off! I should imagine
that this would be a rather expensive mistake?!

It also provides an end plate for fin and so potentially
reduces drag, although I'm not sure by how much.


At 11:06 26 October 2004, Stefan wrote:

>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
>
>

[Derrick Steed]

What about the pilatus B4 then?

Rgds,

Derrick Steed

[Brian Case]

Additionally the T-Tail acts like a large Winglet on the end of the
vertical stab and improves the effectiveness of the vertical Stab and
Rudder. Also it only has 2 intersections as opposed to 4 on a
conventional tail. Plus it is easier to mount a one piece removable
stab on top rather than in the middle of the vertical stab.

Brian


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

[Simon Walker]

Or even the Salto


At 12:48 26 October 2004, Derrick Steed wrote:
>What about the pilatus B4 then?
>
>Rgds,
>
>Derrick Steed
>
>
>
>
>

[Jim Vincent]

>>What about the pilatus B4 then?

It has a T-tail too;-)

Seriously, every design is a trade off between structural weight and
performance issues such as wetted area and configuration.

The B-4 is an aerobatic glider with very good glider performance, about 35:1.
It has a shorter distance from wing to tail compared to most gliders and a
larger cross section. That allows the structure to handle the torsional forced
induced by the T-tail. In fact there are two models, one for limited
aerobatics, the other for full. The main difference is a stiffening plate at
the tail.

Jim Vincent
N483SZ

[Peter Seddon]

"Derrick Steed" > wrote in message
...
> What about the pilatus B4 then?
>
> Rgds,
>
> Derrick Steed
>
Whats your point the B4 is a T Tail, I fly one

Peter.

[Peter Seddon]

"Peter Seddon" > wrote in message
...
>
> "Derrick Steed" > wrote in message
> ...
>> What about the pilatus B4 then?
>>
>> Rgds,
>>
>> Derrick Steed
>>
> Whats your point the B4 is a T Tail, I fly one
>
> Peter.
Oh you mean modern, well it is of sorts.

Peter.

[Peter Seddon]

"Jim Vincent" > wrote in message
...
>>>What about the pilatus B4 then?
>
> It has a T-tail too;-)
>
> Seriously, every design is a trade off between structural weight and
> performance issues such as wetted area and configuration.
>
> The B-4 is an aerobatic glider with very good glider performance, about
> 35:1.
> It has a shorter distance from wing to tail compared to most gliders and a
> larger cross section. That allows the structure to handle the torsional
> forced
> induced by the T-tail. In fact there are two models, one for limited
> aerobatics, the other for full. The main difference is a stiffening plate
> at
> the tail.
>
> Jim Vincent
> N483SZ
>

There are actually 3 variants 4 if you count the fixed U/C one
they are
B4 PC11
B4 PC11A
B4 PC11AF

Peter.

[Jim Vincent]

>There are actually 3 variants 4 if you count the fixed U/C one
>they are
>B4 PC11
>B4 PC11A
>B4 PC11AF
>
>Peter.
>

Hey Peter...I missed that! I never knew there was a fixed gear version.

I had a B4 for a few years and I think it was the best metal work I've ever
seen.

Come to think of it, I once saw a yellow one and a white one, so that makes it
five ;-)

Jim Vincent
N483SZ

[Derrick Steed]

>>Whats your point the B4 is a T Tail, I fly one

Someone implied that aerobatic gliders don't have T tails.


Rgds,

Derrick Steed

[Shawn]

Marian Aldenhövel wrote:
> 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?

Aerodynamics, Ha! It looks cool. That's what sells gliders.
;-)

Shawn

[Stefan]

Derrick Steed wrote:

> Someone implied that aerobatic gliders don't have T tails.

It was me. I wrote: Any *serious* aerobatic plane ... etc. The point is,
the B4 was *not* designed as an acro glider. Only later they found that
due to it's superior handling it would make an ideal acro glider. The
structure had to be reinforced, though, to allow flick maneuvres ...
exactly because of the huge torque forces caused by the T-tail.

BTW: There are many gliders which are certificated for some acro
figures: ASK-21, DG-500, DG-1000 just to name a few. All of them have
T-tail, none of them is primarily an acro glider, all are cross country
gliders which just happen to be allowed for some simple acro figures,
and, you guessed it, none of them is certificated for flick maneuvres.

Stefan

[Marc Ramsey]

Stefan wrote:
> BTW: There are many gliders which are certificated for some acro
> figures: ASK-21, DG-500, DG-1000 just to name a few. All of them have
> T-tail, none of them is primarily an acro glider, all are cross country
> gliders which just happen to be allowed for some simple acro figures,
> and, you guessed it, none of them is certificated for flick maneuvres.

The flight manual for my T-tailed DG-303 Acro allowed flick maneuvers
and tail slides...

Marc

[Stefan]

Marc Ramsey wrote:

> The flight manual for my T-tailed DG-303 Acro allowed flick maneuvers
> and tail slides...

Lucky you. Lucky me that I didn't explicitely mention the DG-300.

Seriously, I only wanted to say that all airplanes which are primarily
designed for serious, competitive aerobatics have a "conventional" tail.
All which I know, that is. (And yes, the salto has a V-tail, which isn't
worse, torqueforcewise.)

Of course there are many airplanes with T-tail which are allowed for
aerobatics to some degree, and some might even be allowed for flick
maneuvres.

What was the question again? Ah, pros and cons of T-tail vs. conventional.

Stefan

[Jim Britton]

FYI: Flick half rolls are allowed in the DG-1000 (18M).

>BTW: There are many gliders which are certificated
>for some acro
>figures: ASK-21, DG-500, DG-1000 just to name a few.
>All of them have
>T-tail, none of them is primarily an acro glider, all
>are cross country
>gliders which just happen to be allowed for some simple
>acro figures,
>and, you guessed it, none of them is certificated for
>flick maneuvres.
>
>Stefan
>
>

[Gerhard Wesp]

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!

[Jim Vincent]

>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

[Chris Nicholas]

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.

[Stefan]

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

[Jim Vincent]

>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

[F.L. Whiteley]

"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

[Jim Vincent]

>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

[John Giddy]

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
>

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 Vincent]

>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

[JonB]

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.

[John Giddy]

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.

[Bruce Greeff]

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.

[John Giddy]

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.

[Jim Vincent]

>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

[Marian Aldenhövel]

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."

[Peter Wyld]

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.

[Gerhard Wesp]

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!

[Udo Rumpf]

> 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

[Bob Kuykendall]

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 here:

http://www.soaridaho.com/Schreder/Schreder/Soaring_Aug_1976_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*

[Mark James Boyd]

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

[Doug Hoffman]

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

[Steve Bralla]

(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

[Eric Greenwell]

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

[Jim Vincent]

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

[Jim Vincent]

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

[F.L. Whiteley]

"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

[F.L. 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

[Bruce Greeff]

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... ;-)

[Buck Wild]

(JonB) wrote in message >...
> 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

[John Giddy]

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

[Bob Kuykendall]

[Warning: somewhat long off-topic ramble ahead]

Earlier, Doug Hoffman > wrote:

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

That's my experience as well, but I think that it has more to do with
the lightweight-yet-rugged aluminum semi-monocoque aft fuselages that
Dick Schreder hung on his gliders. :) I've never personally seen a
Schreder aft fuselage crumpled aft of about the wing root; and yet
I've seen plenty of composite tailbooms broken at or near the fin
root.

One of the substantial issues is how you mass-balance the controls,
and how much. It's easy to look at the centroids of a pair of diagonal
surfaces, and note that it is closer to the fuselage axis than the
centroid of a pair of T-tail surfaces. However, the weight of the
actual tail surfaces often has very little correspondence with the
centroid.

With the Schreder V-tail surfaces in particular, the chunks of
mass-balance lead on the ruddervator end plates move the center of
mass of the combined stabilizer/ruddervator pretty far from the axis
of the fuselage.

With a T-tail, the envelope of the vertical fin gives you some good
opportunities to move the balance masses closer to the axis of the
fuselage. With the rudder, you can concentrate the mass near the lower
hinge. And for the elevator you can either locate the mass balance at
the bellcrank at the fin root, or as in the case of the later LS
gliders just use the elevator push-pull tube itself as the mass
balance.

Of course, the most effective (some might say the only effective) mass
balance is to distribute the counterweight along the hinge line of the
surface. However, the practical experience of the European
manufacturers seems to be that concentrated mass balances can be
adequate if implemented correctly on relatively stiff control
surfaces.

On the other hand, and I think this is what Doug is pointing out, the
thing to watch out for is not necessarily the distance between the
center of mass of the tail surfaces and the fuselage axis. For
groundloop resistance, the distance between the center of mass of the
tail surfaces and the plane of the waterline of the fuselage gets
important. That's the plane (plus and minus a few degrees for dihedral
and wing flex, of course) in which lateral groundloop forces are
applied to the tailwheel. And with a V-tail, the center of mass will
be closer to the waterline plane than to the fuselage axis (by a
factor of .707 for a 90-degree included angle like Dick always used).

As an aside, when Stan Hall located the balance masses at the outboard
ends of the tail surfaces on his pretty little Ibex, he experienced a
flutter mode in which the slender tailboom flexed in torsion. Since he
was using all-moving tail surfaces, he was able to fix the problem by
moving the mass balance weights to the inboard ends of the
stabilizers. His tailboom was more slender than Dick's RS-15 boom, and
much more slender than Dick's semi-monocoque tails, though, so I don't
consider his experience to be particular cause for worry in the HP
world.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24

[Doug Haluza]

A wake vortex is generated at each end of a wing generating lift in a
free flow. So the vortex is generated at both ends of the fin, not
just the "tip". Therefore, the T-tail does not produce one less
vortex. Also, since the vertical stab is usually at zero angle of
attack (except when maneuvering or flying with one wing low) there is
no vortex most of the time, anyway. So this is not a factor at all.

However, the horizontal stab is normally at negative angle of attack,
generating a down force. So vertical stabilizers on the end of the
horizontal stab could reduce these vortices. The tradeoff in extra
section thickness, and interference drag may offset this. For a
T-Tail, it would make the whole Torque/Moment thing much worse as
well.

(JonB) wrote in message >...
> 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.

[Eric Greenwell]

Doug Haluza wrote:
> A wake vortex is generated at each end of a wing generating lift in a
> free flow. So the vortex is generated at both ends of the fin, not
> just the "tip". Therefore, the T-tail does not produce one less
> vortex. Also, since the vertical stab is usually at zero angle of
> attack (except when maneuvering or flying with one wing low) there is
> no vortex most of the time, anyway. So this is not a factor at all.

The Fundamentals of Sailplane design (pages 147-148) has a discussion of
the empennage types. A selective summary of this is..

* the conventional tail (fuselage mounted) isn't used because of poor
ground clearance
* the cruciform tail (ASW-17, Liable) improves the clearance but creates
increased interference drag due to the four corners created at the
intersection of the horizontal and vertical stabilizers
* the Vee tail is the most difficult to achieve the desired spin and
other control responses and tends to have higher induced drag
* the T-tail avoids all the above, with the high placed weight of the
horizontal surface being the main challenge

Not addressed in the FOSD book, but as Bob K mentions (and Waibel and
others), other factors affect the designers choices, such as aesthetics
and manufacturing costs.



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

Eric Greenwell
Washington State
USA

[Marian Aldenhövel]

Hi,

> So why did you say it!

To fill the white space at the bottom of postings, to waste bandwidth
and to confuse readers.

Oh, and it is somewhat on topic because I got it from

http://www.mountainflying.com/mountology.htm

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."

[Gail Stevens]

> "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."

So why did you say it!

:)

sorry couldn't resist...

Gail

[Robert Ehrlich]

Udo Rumpf 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?
>
> 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

The V-tail is inherently less efficient than tails with separate horizontal
and vertical surfaces (conventional and T tails) as a pitch stabilizer.
For any speed except maybe just one, the horizontal stabiliser has to provide
some vertical force in order that the glider remain trimmed. But in order to
obtain the same vertical force from a V-tail, the normal forces on both surfaces
need to be higher than the half of the total vertical force, because only their
vertical component is useful, there are also horizontal components which cancel
each other. But this increased normal force is lift and so produces an increased
induced drag.

Not very important if the V is very flat, but then the efficiency in yaw control,
i.e. as a rudder and fin, is poor and a similar argument may be developed: now we
are interested in the horizontal component and the vertical (higher) components are a
nuisance increasing induced drag. However no such component exists in steady straight
flight, so the inconvenience is less important.

It may happen that in a very well suited situation of steady turn the above argument
may be reversed in favor of V-tails: other tails need down elevator forces and outside
turn rudder force, the resulting force being closer to the horizontal direction than both
the preceding one could be provided with less induced drag by just one of the ruddervators
if properly oriented. But I think that in performance oriented designs the priority is
to minimize the drag in straight flight, and anyway this would be in favor of V-tail just
for (some range around) some very well suited bank angle and speed.
,

[Nyal Williams]

At 11:24 02 November 2004, Marian_Aldenhövel wrote:
>Hi,
>
>> So why did you say it!
>
>To fill the white space at the bottom of postings,
>to waste bandwidth
>and to confuse readers.

Sorry! That's the wrong 'it.' The 'it' in question
is the hypothetical 'it' referred to in your quote
rather than the quote itself.

I'd guess the answer is because you didn't run the
hypothetical statement past the 'hypothetical' editor
in your mind before you uttered it -- an all too common
failing. <grin>

>
>Oh, and it is somewhat on topic because I got it from
>
> http://www.mountainflying.com/mountology.htm
>
>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.'
>

[Udo Rumpf]

"Robert Ehrlich" > wrote in message
...
> Udo Rumpf 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?
>>
>> 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
>
> The V-tail is inherently less efficient than tails with separate
> horizontal
> and vertical surfaces (conventional and T tails) as a pitch stabilizer.
> For any speed except maybe just one, the horizontal stabiliser has to
> provide
> some vertical force in order that the glider remain trimmed. But in order
> to
> obtain the same vertical force from a V-tail, the normal forces on both
> surfaces
> need to be higher than the half of the total vertical force, because only
> their
> vertical component is useful, there are also horizontal components which
> cancel
> each other. But this increased normal force is lift and so produces an
> increased
> induced drag.
>
> Not very important if the V is very flat, but then the efficiency in yaw
> control,
> i.e. as a rudder and fin, is poor and a similar argument may be developed:
> now we
> are interested in the horizontal component and the vertical (higher)
> components are a
> nuisance increasing induced drag. However no such component exists in
> steady straight
> flight, so the inconvenience is less important.
>
> It may happen that in a very well suited situation of steady turn the
> above argument
> may be reversed in favor of V-tails: other tails need down elevator forces
> and outside
> turn rudder force, the resulting force being closer to the horizontal
> direction than both
> the preceding one could be provided with less induced drag by just one of
> the ruddervators
> if properly oriented. But I think that in performance oriented designs the
> priority is
> to minimize the drag in straight flight, and anyway this would be in favor
> of V-tail just
> for (some range around) some very well suited bank angle and speed.

Robert
You are right on all counts.
I think it is still worse due to the fact the elevator and rudder action
has to be combined.
The elevator/rudder chord for the HP V Tail, for example, is 55% chord at
the tip and
45% at the root. The size is dictated due to the combined controls when max
deflexion
is required for both controls, as deflection has to stay around 25 to 30
deg.

To compare the elevator and ruder of a modern T tail which has only 25%
chord and 30%
respectively, which allows for a substantial laminar flow region on both
fixed surfaces.
There is also no question as to the superiority of the T tail regarding the
interference drag.
The T juncture on a T tail is more efficient then the V juncture,
due to the T tail surfaces being aerodynamically off set, also the total
wetted area is less.
Regards
Udo