What happens if a sailplane has no horiz stabilizer or elevator?

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.

Nature gave birds the horizontal stabilizer, I'll stick with the birds.
"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.






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At first glance I would want some reassurance about
the the spinning characteristics and recoverability
of a weight shift pitch control glider with a conventional
wing section! Also I wouldn't fancy flying it inverted.
I think you are proposing a highly unstable and unworkable
configuration i.e. a deathtrap.

The longitudinal control would work differently at
different pitch angles. In a vertical climb or dive
there would be no 'elevator' control. In a steep dive
spin recovery the conventional wing section would bunt
uncontrollably past the vertical. The weight in the
tail would then reverse its effect and increase the
negative g loads. I think it would be so violent that
the glider wings would depart immediately but even
if they didn't you would be in a non recoverable position
just waiting to exceed VNE sufficiently for the wings
to come off a second or two later.

In fact even trying to fly in a fairly level attitude
would be extremely difficult as any forward pitching
would diminish the effect of the weight 'elevator/tailplane'
so that you would then have to send it back past the
postion of stable level flight just to stop the nose
continuing to drop. Then there's the difference in
control forces that would be needed to shift the weight
up and down the tailboom at different pitch attitudes.

Then there's high speed cruising which would increase
the pitching effect of the wing so that the weight
would have to go further and further back as the speed
increased (even neglecting pitch change effects as
above) so the faster you go the futher back the stick.


Conventional glider wing sections are unstable in pitch
and the advantage of an aerodynamic pitch trim and
control device is that it increases its effect with
airspeed and works in all attitudes. If you want to
get rid of the tail you need to use a flying wing chord
section or to use thrust vectoring (maybe that could
be a use for the jet on the other thread but it wouldn't
be a glider)

John Galloway

At 22:24 11 January 2004, Mark James Boyd wrote:
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.

In article ,
John Galloway wrote:
At first glance I would want some reassurance about
the the spinning characteristics and recoverability
of a weight shift pitch control glider with a conventional
wing section! Also I wouldn't fancy flying it inverted.
I think you are proposing a highly unstable and unworkable
configuration i.e. a deathtrap.

The longitudinal control would work differently at
different pitch angles. In a vertical climb or dive
there would be no 'elevator' control. In a steep dive
spin recovery the conventional wing section would bunt
uncontrollably past the vertical. The weight in the
tail would then reverse its effect and increase the
negative g loads. I think it would be so violent that
the glider wings would depart immediately but even
if they didn't you would be in a non recoverable position
just waiting to exceed VNE sufficiently for the wings
to come off a second or two later.

Hmmm...excellent points. I can see that both weight
shift and ducting have problems in spin recovery (a
very important area).

So two more ideas for getting around having a tail
in the way of turbine temps.:

1. Mount the turbine slightly "cockeyed" a few degrees so
the blast isn't right at the tail. Needs some rudder
for powered flight, and doesn't look elegant,
but it's a simple solution to implement.

2. Use a canard. Has anyone ever made a glider with
a canard for control before? I'm guessing maybe not
since there are some obvious disadvantages in a glider
(landouts, aerotow, turbulence caused by a canard)...

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.

One of the guys at the forefront of tailless sailplane
design is Jim Marske. He's been experimenting with
most of the ideas you bring up, including the movable
trim weight. He regularly offers seminars on tailless
sailplane design.

Bob K.
http://www.hpaircraft.com

On Sun, 11 Jan 2004 17:11:11 -0800, "Gary Boggs"
wrote:

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

Interference drag is pretty bad in both cases.

Bye
Andreas

Check out the German Horten's from WWII. They test flew flying wings
as gliders and were planning jet versions. Very interesting piece
discussing them on the History Channel this evening.

Chip Fitzpatrick

"Mark James Boyd" wrote in message
news:4001f9e3$1@darkstar...


2. Use a canard. Has anyone ever made a glider with
a canard for control before? I'm guessing maybe not
since there are some obvious disadvantages in a glider
(landouts, aerotow, turbulence caused by a canard)...


Yep, Burt Rutan. The Solitaire. Good designer, but this effort was not
covered with glory. Gliders need to fly right at the edge of a stall.
http://www.sailplanedirectory.com/zwfmot.htm

Larry Pardue 2I

The Horten flying wings utilized a non-optimal spanload distribution
(wingtips loaded downward) in order to be stable, effectively a tail at
the wingtips. Because of this, their performance was not particularly good.

The Swift (see reference below) is a more modern flying wing that
addresses some of the shortcomings of the earlier ones.
http://aero.stanford.edu/Reports/SWIFTArticle1991.html

Other tailess glider variations were done by Al Backstrom (the Flying
Plank) and Jim Marske (Pioneer & Monarch).
http://www.nurflugel.com/Nurflugel/F..._backstrom.htm
http://www.flyingacesclub.net/alamo/...gwingstuff.htm
http://www.continuo.com/marske/

or for the committed flying-wing person:
http://www.nurflugel.com/nurflugel/nurflugel.html

- - - - - - -

Moving of weights within a fuselage (or other part of the aircraft) is
not a viable solution. Response needs to be quick and reliable, even
for unusual attitudes.

- - - - - - -

Based on the vast majority of the gliders in existance, however, using a
correctly-sized tail is not a bad way to go. Remember, if you don't
truly enjoy what you're flying, you probably won't fly it long. Tailed
aircraft are probably easier to make fly good.


...... Neal

Mark James Boyd wrote:

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.