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

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

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

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?

I'd imagine it will behave the same as an attached one pound ballast
weight on the upper part of the rudder of the glider used to
balance the rudder. Perhaps I'm missing your point here...


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.


Now this a very interesting point. Whether the weight is above
or below the C.G. seems to also have an effect. Thank you
Andreas...

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.

It seems this weight shift idea is just a very fine refinement.
It's intention is to reduce that tiny bit of additional
drag caused by moving surfaces or trim. I agree this is
not anywhere near "the most important invention," but just a
fun winter mind-teaser.

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.

Well, it has worked to improve the efficiency in cruise of
modern jet airliners, and has helped my fuel efficiency in
my 172 across the country, but perhaps, as you point out, not
as a primary control (for pitch in these cases). Except for
ultralights and powered parachutes (which have a low hanging weight)
we don't see it used in modern aircraft.
Perhaps you are right, the standard glider design
(with no low hanging weight) doesn't lend itself well
to this means of control...

Andreas

Thanks for your thoughts!

Mark

On 18 Jan 2004 11:53:31 -0700, (Mark James Boyd)
wrote:


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?

I'd imagine it will behave the same as an attached one pound ballast
weight on the upper part of the rudder of the glider used to
balance the rudder. Perhaps I'm missing your point here...

You are correct - but you have the horizontal stab that dampens the
motion (remember that the whole fuselage and tail acts as a weight!).

This is the cause why you need something aerodynamical to control your
pitch, and why weight shifting does not work.

It does not matter whether the damping is done by a horizontal
stabilizier or the airfoil/wing design of a flying wing.


Now this a very interesting point. Whether the weight is above
or below the C.G. seems to also have an effect.

Yes - and don't forget that the control authority of hang gliders is
extremely limited. If the gravity vector is not pointing "downwards"
(seen from the pilot's coordinate system) they have absolutely no
control at all. Inverted flight is out of question, and they are able
to fly their loopings only with some tricks.


It seems this weight shift idea is just a very fine refinement.
It's intention is to reduce that tiny bit of additional
drag caused by moving surfaces or trim. I agree this is
not anywhere near "the most important invention," but just a
fun winter mind-teaser.

This is what is already being done - by water ballast in the tail that
fixes the CG at a position that is close to perfect for all flight
situations.
There have already trials been made (with ASH-25) to determine the
influence of performance of different CG positions in different
situations (cruise, climb, thermalling), and the inluence was nearly
immeasurably if the CG was moved to a supposedly "more optimum"
forward position during cruise.
The performance gain in a glider with rearward CG is (as you point out
for Cessan and airliners) often dramatic, especially in climb rate.




Bye
Andreas

"Andreas Maurer" wrote in message
...
On 18 Jan 2004 11:53:31 -0700, (Mark James Boyd)
wrote:


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?

I'd imagine it will behave the same as an attached one pound ballast
weight on the upper part of the rudder of the glider used to
balance the rudder. Perhaps I'm missing your point here...

You are correct - but you have the horizontal stab that dampens the
motion (remember that the whole fuselage and tail acts as a weight!).

This is the cause why you need something aerodynamical to control your
pitch, and why weight shifting does not work.

It does not matter whether the damping is done by a horizontal
stabilizier or the airfoil/wing design of a flying wing.


Now this a very interesting point. Whether the weight is above
or below the C.G. seems to also have an effect.

Yes - and don't forget that the control authority of hang gliders is
extremely limited. If the gravity vector is not pointing "downwards"
(seen from the pilot's coordinate system) they have absolutely no
control at all. Inverted flight is out of question, and they are able
to fly their loopings only with some tricks.

Twaddle !
There are guys who fly HG inverted (they are complete nutters, but the point
is, it can be done)
Looping a HG requires 2 things,
1) speed
2) balls
fly very very, very fast, allow the bar to come forwards _slowly_ then
accelerate towards a full aft CofG position in a _controlled_ manner. (that
way you can do 54 consecutive loops in a HG) ((if you start high enough))

The CofG on a tailess aircraft (i.e. hangglider) is only secondary in the
control of VNE and stall, CofG is used for trimming but the primary speed
control of the wing is performed by the washout at the tips and on older
gliders through "luff lines" acting as "up elevator" as the speed built up
(not really used much these days)

bottom line, with a swept wing platform you can _make_ it operate within a
set airspeed range by limiting it's AUW and setting the AofA along the wing
section.

regards
Roy

On Mon, 19 Jan 2004 17:51:30 +0000 (UTC), "Roy"
wrote:


Twaddle !
There are guys who fly HG inverted (they are complete nutters, but the point
is, it can be done)

I'm talking about a *sustained* inverted flight, not a 4g loop where
the inverted part takes one second.

The loops you describe can also be done with a paraglider (where
inverted flight is obviously a little... problematic).



Bye
Andreas

Andreas Maurer writes:


This is the cause why you need something aerodynamical to control your
pitch, and why weight shifting does not work.


Remember, with weight-shift control, if you are weightless, you are out of
control. That's why it gets very "interesting" in a hang glider whenever you
go weightless.

Steve