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

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

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

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.

Neal Pfeiffer wrote in message om...


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.
************************************************** *****************************
Moveable weights for pitch control aren't as responsive in the
negative pitch airfoils used in conventional gliders because
increasing speed increases the downward pitching moment which the wing
produces. Moving the weight forward to drop the nose and increase
speed leads to the requirement for back stick to increase downward
pressure on the horizontal stab and keep the nose from continuing to
drop. If you tried to do this only with weight shift, you would need
to move the weights forward to increase speed and then progressively
move the weight backward as the speed builds up just to maintain
stability. Computerized fuel shifting on airlines does this but they
still use all-flying-tails for the fine corrections.

Weight shifting for pitch control is very workable in flying-wing type
gliders as they are very responsive to changes in cg; and the inherent
stability of the reflex wing keeps the glider very close to the weight
shifted pitch.(and speed) Several Genesis owners use rudimentary forms
of weight shift on a regular basis. One has mentioned putting ankle
weights on the rudder pedals and moving them back and forth, someone
else has stated in the GenesisFlyers Yahoo Groups site that inflating
the lumbar support adds 4 knots to the trimmed speed. There have been
discussions about using nose and tail water tanks and shifting from
one to the other to trim for best thermalling or high speed. This is
a very workable improvement for Genesis 2 and Marske Pioneer type
gliders. Weight shifting on the Pioneer may work even better as it
may be possible to fly with a very aft cg which keeps the nose high
and then use forward stick to deflect the elevators down increasing
the lift coeffecient of the wing. Moving the weight forward would then
allow it to fly fast with the elevators slightly raised the way
flapped gliders fly with negative flaps.(reflex)

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.
************************************************** ******************************
It's hard to argue against correctly-sized tails, although I suspect
that what you call "correctly-sized" is what I spitefully and
maliciously call a boomsnapper. Boomsnappers interfere with low
energy landings as your pitch at flair is limited by your willingness
to slam down tail first and damage the boom. Some boomsnappers (G
102) are speed limited because, oops!, the elevator isn't as strong as
we thought and it is prone to flutter. The G103 Acro is acro no more
because that big heavy extremely strong tail boom isn't as strong as
it should be. Need to slap on a few more layers of carbon so's it
don't come off.
So, how strong and durable are those tiny, light weight tail booms on
newer high performance gliders? Are they at least as strong as the
wing spars on Shemp-Hirth gliders? How strong will they be when they
are as old as Grobs?
Got to keep that tape on tight, too, cause lifting of the front edge
of tape near the elevator causes an almost total loss of elevator
authority.
Genesis 2 and Pioneer owners all seem to really like the handling
characteristics of their flying-wing gliders and as a group they don't
seem to miss or wish they had longer tail booms.

Long tailed aircraft are certainly easier to make and they satisfy an
esthetic which sees ships, trains and trucks as boxes or tubes which
carry cargo, so an aircraft should be a box or tube with wings. The
more it looks like a truck the safer it "feels".

Mark,

I've been hitting the books lately. I've just read Aerodynamics for
Naval Aviators (ASA). An excellent treatment of aerodynamics for the
aviator without the oversimplification one typcially sees in most
"learn to fly" books.

It has sections on static and dynamic stability that will help give
you a better grounding for exploring the questions you've asked. And
frankly, it's not bad reading. I was very surprised. Not nearly as
dessicated as I feared. A good addition to any pilot's personal
library.

BTW, it's easy to do the math to figure out what kind of loads you'll
need to produce on the tail to maintain pitch control. Use your weight
and balance calculations to exptrapolate approximations of the moment
arm between cg and center of lift, then match torques with the tail's
moment arm. Repeat this process for a load factor of two or three
(steep turns) and you'll find that you'll need to move a lot of mass
quickly and quite a distance to stay in trim. Just not very practical.
But interesting thoughts.

OC

In article ,
Chris OCallaghan wrote:
Mark,

I've been hitting the books lately. I've just read Aerodynamics for
Naval Aviators (ASA). An excellent treatment of aerodynamics for the
aviator without the oversimplification one typcially sees in most
"learn to fly" books.

An excellent book. The only place I found the equation for
the relationship between weight and stall speed. Good
stuff about the different effects of different types of
flaps. Too bad it's buried in the "abyss" (my garage)
due to new space needs (bassinet, changing table, laundry basket,
mom's cozy chair...)



New pilots aren't hard to train, but they sure take a long
time to GROW!

Whoops, a case of typing faster than I was thinking... Ignore the
second half of the last paragraph... it's a misplaced fragment from
another train of thought.

(Chris OCallaghan) wrote in message . com...
Mark,

I've been hitting the books lately. I've just read Aerodynamics for
Naval Aviators (ASA). An excellent treatment of aerodynamics for the
aviator without the oversimplification one typcially sees in most
"learn to fly" books.

It has sections on static and dynamic stability that will help give
you a better grounding for exploring the questions you've asked. And
frankly, it's not bad reading. I was very surprised. Not nearly as
dessicated as I feared. A good addition to any pilot's personal
library.

BTW, it's easy to do the math to figure out what kind of loads you'll
need to produce on the tail to maintain pitch control. Use your weight
and balance calculations to exptrapolate approximations of the moment
arm between cg and center of lift, then match torques with the tail's
moment arm. Repeat this process for a load factor of two or three
(steep turns) and you'll find that you'll need to move a lot of mass
quickly and quite a distance to stay in trim. Just not very practical.
But interesting thoughts.

OC

Mark James Boyd wrote:

I'm considering these factors, because eliminating the
elevator and stab would reduce drag.

That's right.

You should also consider eliminating the wings, that would reduce even
more drag.

I suppose the best way to experiment with this is in a
model glider first,

Well... I suppose too... if you want to experiment this with a full
scale glider, it will be difficult to find a pilot to put in ;-)


--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

In article ,
Denis Flament wrote:
Mark James Boyd wrote:

I'm considering these factors, because eliminating the
elevator and stab would reduce drag.

That's right.

You should also consider eliminating the wings, that would reduce even
more drag.

An interesting, but more challenging, idea...
An aerodyne without wings...hmmm...


I suppose the best way to experiment with this is in a
model glider first,

Well... I suppose too... if you want to experiment this with a full
scale glider, it will be difficult to find a pilot to put in ;-)

Denis

Hmmm...methinks some sort of pully system in a plain old glider
might do it. Get a weight of the right size so that
if it lodges in the tail, you are still within safe CG, and if
it lodges in the nose, you are still within safe CG.

Maybe this is only a 1 pound weight. Then have an additional control
which moves this weight. Go up to altitude and see if moving
this weight gives sufficient control.

The biggest safety feature would be ensuring the weight didn't
come loose during a critical phase of flight (near the ground)
and your supplementary "weight" cables don't hinder
the original controls in any way...

A weight right in the tail which moves maybe 3 feet forward
when the auxiliary stick is moved might do it. Hmmm...

On 14 Jan 2004 20:15:24 -0700, (Mark James Boyd)
wrote:

Hmmm...methinks some sort of pully system in a plain old glider
might do it. Get a weight of the right size so that
if it lodges in the tail, you are still within safe CG, and if
it lodges in the nose, you are still within safe CG.

Maybe this is only a 1 pound weight. Then have an additional control
which moves this weight. Go up to altitude and see if moving
this weight gives sufficient control.


Just imagine what forces your movable weight will exert under a g load
different than 1? For example, when you are flying through a vertical
gust?

This is precisely the cause why your idea cannot work - and why the
pilot of a hang glider is hanging so far *below* his wing.



The biggest safety feature would be ensuring the weight didn't
come loose during a critical phase of flight (near the ground)
and your supplementary "weight" cables don't hinder
the original controls in any way...

A weight right in the tail which moves maybe 3 feet forward
when the auxiliary stick is moved might do it. Hmmm...


Have you ever thought about what is regarded as the most important
invention of the Wright brothers?
You name it - aerodynamical control around all three axes.

There's a good cause why there was never such a system that ever
worked on an aircraft, although thousands of designers have tried it
in the pas 120 years.


Bye
Andreas