horiz tail airfoil observations

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...