V tail or twin rudders on the ends of the horizontal stabilizer makes the
most sense to me.


"Mark James Boyd" wrote in message
news:4001c97d$1@darkstar...
There are some designs which have no horizontal stab: flying wings
for example. There are also canard setups (the speed canard, for example).

For a sailplane, I was thinking about how one might design away
the typical T-tail stabilizer and elevator.

First of all, how much dynamic stability does the horiz. stab
contribute? If it were eliminated by design, would it
be absolutely necessary to compensate by using a swept
wing (either forward or backward)? When deflected,
how much torque does an elevator provide?

I'm considering these factors, because eliminating the
elevator and stab would reduce drag. From there, one
could potentially design a ducted surface, or use moveable
weights in the tail to change C.G and therefore pitch.

In the first case (ducting), there are commonly used
NACA ducts (they look like little triangles on
power planes) that are commonly used as air vents on
power planes. They have the advantage of producing minimal
drag when the vent is closed. On a glider, they could be
used in the tail to direct airflow and produce pitching
moments. There is a tail-rotor free turbine helicopter
which uses ducted bleed-air, I believe, to control yaw this way.

The other option, which is more elegant, is to use a moveable
weight in the tail for pitch. Move the weight forward to
pitch down, backward to pitch up. One difficulty is
if the weight must be quite heavy, or the stick movement
needed to move it is too heavy. I suppose this in some
part is a function of the length of the tailboom. Another
complication is that a regular elevator is more effective at
high airspeed, and less effective at low airspeed (more
deflection is required for the same torque). This isn't
necessarily true with a weight-shift pitch control.

Hmmm...anyone have data about forces provided by the
elevator is flight? Drag caused by the elevator/ vert. stabilizer
in level flight? How about torque produced by weight shift
near the arm of the elevator?

I suppose the best way to experiment with this is in a
model glider first, then in a full scale glider with BOTH
pitch systems (elev/stab, AND weight shift). Then finally
with the elev/stab removed.