Had a look at Amazon: The Fundamentals of Sailplane Design, Fred Thomas &
Judah Milgram

--
Bert Willing

ASW20 "TW"


"Gldcomp" a écrit dans le message de
. com...
Bert,

I'm sorry, you are not correct or not expressing yourself correctly.
I'm not expressing an oppinion here, I'm telling you how it is.

The CG is by design located ahead of the Neutral Point of the glider
(otherwise the glider would be uncontrollable), so, it has the overall
tendency to push the nose of the glider down, since the Neutral Point is
the
place where all the Lift is acting.
To counteract this force, the tail planes are always pushing the tail
DOWN,
thus keeping the forces balanced.
We vary the amount of down force produced by the tail planes by moving the
elevator with the stick.

When we move the CG aft, we bring it closer to the Neutral Point, which
reduced the required down force produced by the elevator.
In extremeley aft CG situations, the tailplanes MAY IN FACT produce an
overall UP force on the tail, but this is the exception, rather than the
rule.

The more forward the CG position, however, the more DOWN force is
necessary
on the tail.
This is the very reason pilots try to place the CG aft in competition
gliders : so that the elevator doesn't have to produce quite so much DOWN
force on the tail. The result is improved climb because of this.



"Bert Willing" wrote in
message ...
Not quite correct. At high angles of attack, the elevator produces lift
and
at of angle of attack, it produces negative lift. The crossover (i.e.
zero
lift, minimum drag) is a design criterium and is usually placed at the
max
L/D angle of attack. But then, this will of course be influenced by a
large
variation of the CG.

--
Bert Willing

ASW20 "TW"


"Gldcomp" a écrit dans le message de
. com...
Bert,

It has little to do with airspeed. The position of the CG will
determine
the
force on the elevator.


"Bert Willing" wrote
in
message ...
You're right - the elevator produces lift (same direction as the
wings)
at
low speeds, not at high speeds. Got mixed up.

--
Bert Willing

ASW20 "TW"


"Gldcomp" a écrit dans le message de
om...
"Bert Willing"
wrote
in
message ...
That doesn't make sense to me. At high speeds, the elevator
produces
lift
so
in case of structural failure, the bits would go upwards.

--
Bert Willing

ASW20 "TW"

Bert,

The elevator does produce lift, but in the opposite direction as
the
wings
(most of the time anyway).