horiz tail airfoil observations

Brad wrote:
I've been perusing Fred Thomas's Sailplane Design book lately. I am
curious, why do most of the modern sailplanes use a non-symetrical
airfoil for the horiz surface, and most of the "older" sailplanes use a
symetrical airfoil?

I was looking at a Krokus at the Pensacola airshow over the weekend,
made in the 80's, it is definately using somthing like the Wortman
71-150/30 while my glider, and Apis uses an airfoil that is not
symetrical.

Is the fixed portion symmetrical but with a control surface that has a
slight undercamber on the bottom? That's what my ASH 26 elevator is
like, and I believe that is normal.

If the fixed portion is not symmetrical, is the flatter part on the top
or bottom?


--
Eric Greenwell - Washington State, USA
Change "netto" to "net" to email me directly

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Eric Greenwell wrote:
Is the fixed portion symmetrical but with a control surface that has a
slight undercamber on the bottom? That's what my ASH 26 elevator is
like, and I believe that is normal.

If the fixed portion is not symmetrical, is the flatter part on the top
or bottom?

I know the ASW27 has a small camber (up side down airfoil)
the 26 would most likely have it too. The Elevator under camber acts
like a servo tap, the faster you go the more up elevator you get when
flying with you hands off the stick, even if the trim spring is all
the way forward. This is a safty feature.
Udo

Is the fixed portion symmetrical but with a control surface that has a
slight undercamber on the bottom? That's what my ASH 26 elevator is
like, and I believe that is normal.

If the fixed portion is not symmetrical, is the flatter part on the top
or bottom?

the fixed portion is pretty much symetrical. the flatter part is on the
top surface

the upper part of the elevator is straight
the lower part of the elevator has a slight undercamber to it, like
what you normally see on the lower surface of a sailplane wing.

--
Eric Greenwell - Washington State, USA
Change "netto" to "net" to email me directly

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Brad wrote:
Is the fixed portion symmetrical but with a control surface that has a
slight undercamber on the bottom? That's what my ASH 26 elevator is
like, and I believe that is normal.

If the fixed portion is not symmetrical, is the flatter part on the top
or bottom?

the fixed portion is pretty much symetrical. the flatter part is on the
top surface

This is consistent with the need to provide a down force, the usual case
for our gliders, so the airfoil is "upside down" compared to the wing.

the upper part of the elevator is straight
the lower part of the elevator has a slight undercamber to it, like
what you normally see on the lower surface of a sailplane wing.

As Udo pointed out, this is how the designer meets the requirement for
increasing "up elevator" force as speed increases. While this has a
safety advantage, the truly determined performance oriented pilot will
sometimes remove the undercamber to reduce drag. I've never wanted to do
it, because I want the safety advantage and I'm concerned the weight of
filler material might make the elevator flutter. It would take some
paperwork to make it legal, too.

--
Eric Greenwell - Washington State, USA
Change "netto" to "net" to email me directly

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org

At a crazier age I tried eliminating all the undercamber in my ASW-25
elevator. This affected the pitch stability so drastically that when the
stick was released the only unknown was whether the impending loop would be
inside or outside! As pointed out, the under camber is there for pitch
stability and with passing decades the German airworthiness authority has
increased the forces. A Janus has lower pitch trim forces than a Duo Discus
for instance.


"Eric Greenwell" wrote in message
news:eFt6h.4796$T_.3143@trndny06...
Brad wrote:
Is the fixed portion symmetrical but with a control surface that has a
slight undercamber on the bottom? That's what my ASH 26 elevator is
like, and I believe that is normal.

If the fixed portion is not symmetrical, is the flatter part on the top
or bottom?

the fixed portion is pretty much symetrical. the flatter part is on the
top surface

This is consistent with the need to provide a down force, the usual case
for our gliders, so the airfoil is "upside down" compared to the wing.

the upper part of the elevator is straight
the lower part of the elevator has a slight undercamber to it, like
what you normally see on the lower surface of a sailplane wing.

As Udo pointed out, this is how the designer meets the requirement for
increasing "up elevator" force as speed increases. While this has a safety
advantage, the truly determined performance oriented pilot will sometimes
remove the undercamber to reduce drag. I've never wanted to do it, because
I want the safety advantage and I'm concerned the weight of filler
material might make the elevator flutter. It would take some paperwork to
make it legal, too.

--
Eric Greenwell - Washington State, USA
Change "netto" to "net" to email me directly

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Hey Karl when you were totally banana's tell us the story of your 15M
ASW17 at 200knots thru the start gate.

Regards

Al



Karl Striedieck wrote:
At a crazier age I tried eliminating all the undercamber in my ASW-25
elevator. This affected the pitch stability so drastically that when the
stick was released the only unknown was whether the impending loop would be
inside or outside! As pointed out, the under camber is there for pitch
stability and with passing decades the German airworthiness authority has
increased the forces. A Janus has lower pitch trim forces than a Duo Discus
for instance.


"Eric Greenwell" wrote in message
news:eFt6h.4796$T_.3143@trndny06...
Brad wrote:
Is the fixed portion symmetrical but with a control surface that has a
slight undercamber on the bottom? That's what my ASH 26 elevator is
like, and I believe that is normal.

If the fixed portion is not symmetrical, is the flatter part on the top
or bottom?

the fixed portion is pretty much symetrical. the flatter part is on the
top surface

This is consistent with the need to provide a down force, the usual case
for our gliders, so the airfoil is "upside down" compared to the wing.

the upper part of the elevator is straight
the lower part of the elevator has a slight undercamber to it, like
what you normally see on the lower surface of a sailplane wing.

As Udo pointed out, this is how the designer meets the requirement for
increasing "up elevator" force as speed increases. While this has a safety
advantage, the truly determined performance oriented pilot will sometimes
remove the undercamber to reduce drag. I've never wanted to do it, because
I want the safety advantage and I'm concerned the weight of filler
material might make the elevator flutter. It would take some paperwork to
make it legal, too.

--
Eric Greenwell - Washington State, USA
Change "netto" to "net" to email me directly

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org

As Udo pointed out, this is how the designer meets the requirement for
increasing "up elevator" force as speed increases. While this has a
safety advantage, the truly determined performance oriented pilot will
sometimes remove the undercamber to reduce drag. I've never wanted to do
it, because I want the safety advantage and I'm concerned the weight of
filler material might make the elevator flutter. It would take some
paperwork to make it legal, too.

--

Eric,
In this case the elevator and the shape is not just for safety but
also to maximize the performance, the airfoil was design as a
complete working unit. If there is a compromise it must be very small.
If you fly with the most optimum C of G there is very little elevator
deflection for the normal climb and speed range in a steady state and
if there is, let say -2 to + 2 deg of defection, I can tell you there
is no measurable drag penalty.
Udo

Udo wrote:
As Udo pointed out, this is how the designer meets the requirement for
increasing "up elevator" force as speed increases. While this has a
safety advantage, the truly determined performance oriented pilot will
sometimes remove the undercamber to reduce drag. I've never wanted to do
it, because I want the safety advantage and I'm concerned the weight of
filler material might make the elevator flutter. It would take some
paperwork to make it legal, too.

--

Eric,
In this case the elevator and the shape is not just for safety but
also to maximize the performance, the airfoil was design as a
complete working unit. If there is a compromise it must be very small.
If you fly with the most optimum C of G there is very little elevator
deflection for the normal climb and speed range in a steady state and
if there is, let say -2 to + 2 deg of defection, I can tell you there
is no measurable drag penalty.

As I understand it, the drag penalty is not from the elevator deflection
(some of which would be required anyway), but because the airfoil is not
optimum for the lift (down force) it is producing; i.e., the undercamber
is on the side of the airfoil producing lift. There is always some drag
from the elevator, even with the control surface undeflected, because of
the lift (down force) it is producing.

--
Eric Greenwell - Washington State, USA
Change "netto" to "net" to email me directly

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Eric Greenwell wrote:
Udo wrote:
As Udo pointed out, this is how the designer meets the requirement for
increasing "up elevator" force as speed increases. While this has a
safety advantage, the truly determined performance oriented pilot will
sometimes remove the undercamber to reduce drag. I've never wanted to do
it, because I want the safety advantage and I'm concerned the weight of
filler material might make the elevator flutter. It would take some
paperwork to make it legal, too.

--

Eric,
In this case the elevator and the shape is not just for safety but
also to maximize the performance, the airfoil was design as a
complete working unit. If there is a compromise it must be very small.
If you fly with the most optimum C of G there is very little elevator
deflection for the normal climb and speed range in a steady state and
if there is, let say -2 to + 2 deg of defection, I can tell you there
is no measurable drag penalty.

As I understand it, the drag penalty is not from the elevator deflection
(some of which would be required anyway), but because the airfoil is not
optimum for the lift (down force) it is producing; i.e., the undercamber
is on the side of the airfoil producing lift. There is always some drag
from the elevator, even with the control surface undeflected, because of
the lift (down force) it is producing.

--
Eric Greenwell - Washington State, USA
Change "netto" to "net" to email me directly

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Hi Eric - I don't think this is correct. The prototype V2c I flew had a
trailing-edge tab bent down, explained to me as required for
appropriate
stick force gradient, as the elevator undersurface had no camber.
The production V2C tails added back the camber at a minor performance
penalty. Some well-known competition pilots in years back (not just
Karl)
did remove elevator camber for reduced drag, frightening the flutter
experts.

Hope that helps with the mystery,
Best Regards, Dave

PS: Jud, come out of hiding and explain it better to us
engineer-wanabees...

Hi Dave,

Hey...........now that you mention it, the elevator of that Krokus had
a bent down tab along the whole trailing edge, it was about .5" wide. I
don't quite recall if the lower surface of the elevator was flat or
curved tho......................there were 6 Blue Angels screaming by
and I was slightly distracted!

Cheers,
Brad


wrote:
Eric Greenwell wrote:
Udo wrote:
As Udo pointed out, this is how the designer meets the requirement for
increasing "up elevator" force as speed increases. While this has a
safety advantage, the truly determined performance oriented pilot will
sometimes remove the undercamber to reduce drag. I've never wanted to do
it, because I want the safety advantage and I'm concerned the weight of
filler material might make the elevator flutter. It would take some
paperwork to make it legal, too.

--

Eric,
In this case the elevator and the shape is not just for safety but
also to maximize the performance, the airfoil was design as a
complete working unit. If there is a compromise it must be very small.
If you fly with the most optimum C of G there is very little elevator
deflection for the normal climb and speed range in a steady state and
if there is, let say -2 to + 2 deg of defection, I can tell you there
is no measurable drag penalty.

As I understand it, the drag penalty is not from the elevator deflection
(some of which would be required anyway), but because the airfoil is not
optimum for the lift (down force) it is producing; i.e., the undercamber
is on the side of the airfoil producing lift. There is always some drag
from the elevator, even with the control surface undeflected, because of
the lift (down force) it is producing.

--
Eric Greenwell - Washington State, USA
Change "netto" to "net" to email me directly

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Hi Eric - I don't think this is correct. The prototype V2c I flew had a
trailing-edge tab bent down, explained to me as required for
appropriate
stick force gradient, as the elevator undersurface had no camber.
The production V2C tails added back the camber at a minor performance
penalty. Some well-known competition pilots in years back (not just
Karl)
did remove elevator camber for reduced drag, frightening the flutter
experts.

Hope that helps with the mystery,
Best Regards, Dave

PS: Jud, come out of hiding and explain it better to us
engineer-wanabees...