horiz tail airfoil observations

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