J a c k wrote:
>
>> I think the Duo's airbrakes are better than many people think. The Duo is a
>> big heavy glider with lots of inertia. It doesn't like to change direction
>> quickly. That includes its behavior on sudden airbrake deployment. You
>> don't get a lot of sink right away.
>>
>> My first reaction was that the airbrakes were weak but a little more
>> experience showed me that with a little patience, the brakes took effect and
>> produced a respectable decent rate. The Duo just makes you plan ahead a
>> little more than with a light single seater.

I don't understand the physics here.
Consider an analogy:
when the VW-beetle came out it had a reputation of 'turning over easily',
based on the false logic that you need less men to 'turn it over' than to
'pick up & turn over a bigger car'. Of course the forces while driving, that
tended to 'turn it over' were less for a VW, but so too were the forces that
resisted 'turn it over'.
A heavy pendulum is 'eqivalent' to a lighter pendulum.

So too for the BIG glider.
What doesn't scale up is the pilots strength.
Or is reynolds number significant ?

== Chris Glur.

<problems@gmail> wrote in message ...
> J a c k wrote:
>>
>>> I think the Duo's airbrakes are better than many people think. The Duo
>>> is a
>>> big heavy glider with lots of inertia. It doesn't like to change
>>> direction
>>> quickly. That includes its behavior on sudden airbrake deployment. You
>>> don't get a lot of sink right away.
>>>
>>> My first reaction was that the airbrakes were weak but a little more
>>> experience showed me that with a little patience, the brakes took effect
>>> and
>>> produced a respectable decent rate. The Duo just makes you plan ahead a
>>> little more than with a light single seater.
>
> I don't understand the physics here.
> Consider an analogy:
> when the VW-beetle came out it had a reputation of 'turning over easily',
> based on the false logic that you need less men to 'turn it over' than to
> 'pick up & turn over a bigger car'. Of course the forces while driving,
> that
> tended to 'turn it over' were less for a VW, but so too were the forces
> that
> resisted 'turn it over'.
> A heavy pendulum is 'eqivalent' to a lighter pendulum.
>
> So too for the BIG glider.
> What doesn't scale up is the pilots strength.
> Or is reynolds number significant ?
>
> == Chris Glur.

OK, the first post above wasn't too clear and, since it is just speculation,
may not even be correct. Maybe, what the pilot 'feels' when typical air
brakes are deployed is the sudden onset of deceleration. The increase in
sink isn't great enough to feel.

The Duo is heavy, clean and accelerates like a rocket when the nose is down.
The airbrakes don't reduce this much so the deceleration is smaller than
lighter gliders giving the first impression that the brakes are weak. The
rate of sink with air brakes extended is within the normal range gicving a
~7:1 glide which will get you down but won't do a lot to control airspeed.
You still have to control airspeed with pitch.

Bill Daniels

On Wed, 31 Oct 2007 08:31:55 -0600, "Bill Daniels"
<bildan@comcast-dot-net> wrote:

>The Duo is heavy, clean and accelerates like a rocket when the nose is down.
>The airbrakes don't reduce this much so the deceleration is smaller than
>lighter gliders giving the first impression that the brakes are weak.

The strength of the dive brakes can easily be measured by the time it
takes to bleed off excessive speed during the flare.

Let's face it, the Duo flares forever if you are too fast. Other ships
(DG-505, DG-1000, Janus) decelerate much quicker.

Clear case: Weak airbrakes.



Bye
Andreas

> >> I think the Duo's airbrakes are better than many people think. The Duo is a
> >> big heavy glider with lots of inertia.

> I don't understand the physics here.

Like other duo pilots, I notice that the glide angle in a stabilized,
on-the-triangle glide with spoilers open is decently steep, but that
the duo does not slow down quickly if you use spoilers to stop excess
speed, especially in ground effect.

Here's a theory -- or at least the physical possibility of this
observation. Spoilers, true to their name, do two things -- they add
drag and they spoil lift. Since lift = weight, "spoiling lift" really
that induced drag is raised because of the discontinuous lift
distribution at the spoiler position.

Now, it makes sense that the duo spoiler configuration is more
oriented to the production of induced rather than profile drag. The
spoilers are wide (spanwise) but not very deep (up and down). The span
is bigger than your 15 meter glider, so there is less induced drag to
start with, and increasing it is more effective in reducing glide
angle.

If this were the case, we'd expect the spoilers to be less effective
overall at higher speeds, and especially so in ground effect, which
reduces induced drag, but to produce a good glide angle at a
relatively slow approach speed, out of ground effect. This seems to be
about what we observe. This also explains why spoilers on all big
gliders seem less effective at "high parasitic drag" maneuvers.

The bottom line remains, if you fly a duo, accurate speed control in
the pattern is essential. And yes, even if the stabilized glide angle
is the same as other gliders, the spoilers are "less effective"
because bleeding off excess speed is one of the desirable "effects" of
spoilers.

John Cochrane

On Oct 31, 8:36 am, BB > wrote:
> > >> I think the Duo's airbrakes are better than many people think. The Duo is a
> > >> big heavy glider with lots of inertia.
> > I don't understand the physics here.
>
> Like other duo pilots, I notice that the glide angle in a stabilized,
> on-the-triangle glide with spoilers open is decently steep, but that
> the duo does not slow down quickly if you use spoilers to stop excess
> speed, especially in ground effect.
>
> Here's a theory -- or at least the physical possibility of this
> observation. Spoilers, true to their name, do two things -- they add
> drag and they spoil lift. Since lift = weight, "spoiling lift" really
> that induced drag is raised because of the discontinuous lift
> distribution at the spoiler position.
>
> Now, it makes sense that the duo spoiler configuration is more
> oriented to the production of induced rather than profile drag. The
> spoilers are wide (spanwise) but not very deep (up and down). The span
> is bigger than your 15 meter glider, so there is less induced drag to
> start with, and increasing it is more effective in reducing glide
> angle.
>
> If this were the case, we'd expect the spoilers to be less effective
One thing I haven't seen in this discussion is the fact that the Duo's
spoilers are not located right behind the spar. They are located quite
a bit farther aft and thus produce mostly drag and not as much spoiled
lift. I liken them to the H-301 Libelle spoilers that produced mostly
dray and therefore had to be opened earlier and left out longer to get
the same result as, say the H-201 Libelle which had true spoilers
located at the high point of the airfoil.
JJ


> overall at higher speeds, and especially so in ground effect, which
> reduces induced drag, but to produce a good glide angle at a
> relatively slow approach speed, out of ground effect. This seems to be
> about what we observe. This also explains why spoilers on all big
> gliders seem less effective at "high parasitic drag" maneuvers.
>
> The bottom line remains, if you fly a duo, accurate speed control in
> the pattern is essential. And yes, even if the stabilized glide angle
> is the same as other gliders, the spoilers are "less effective"
> because bleeding off excess speed is one of the desirable "effects" of
> spoilers.
>
> John Cochrane

Hi Chris

Lets think it through then. Here is my very rusty attempt at physics -(I know
there are experts here maybe one will bite)

The bigger gliders tend to have higher aspect ratio wings. This means that, like
the Beetle they have a polar moment challenge. The beetle would roll easily at
speed because of a combination of aerodynamics reducing load on the suspension,
and a high centre of gravity. Add the original swing axles and you have a recipe
for landing on the roof.

In the long wings glider you have the same issue, but symmetrical on both sides,
the centre of mass of the wings is at a further distance from the roll centre of
the aircraft. It thus takes more energy to achieve a specific rate of rotation,
because you need more kinetic energy (Mass * distance** is against you because
the wings are longer AND heavier)
Think of two pendulums of equal mass, but different lengths. Then try it with
the same mass but different mass distribution (Like a metronome)
The frequency is proportional to the polar moment not the mass.

I am sure the aerodynamics experts can tell you about the relative Reynolds
numbers, but that is more a function of chord, and that is not radically
different. The taper ratio is higher in 15m than in 26m, but the tips of a given
generation seem to be of similar chord. This is where the ailerons generate the
rolling force so I assume the airfoil differences are greater than the Reynolds
number effects.

What makes it necessary to stay further ahead of a 20m wingspan glider is
inertia - stored energy. It takes longer, and / or more force to achieve the
same deflection. Then you take into account the total mass that you are trying
to deflect is greater and it gets worse.

On the other hand I understand that 47:1 (Duo x) can get addictive.

problems@gmail wrote:
> J a c k wrote:
>>> I think the Duo's airbrakes are better than many people think. The Duo is a
>>> big heavy glider with lots of inertia. It doesn't like to change direction
>>> quickly. That includes its behavior on sudden airbrake deployment. You
>>> don't get a lot of sink right away.
>>>
>>> My first reaction was that the airbrakes were weak but a little more
>>> experience showed me that with a little patience, the brakes took effect and
>>> produced a respectable decent rate. The Duo just makes you plan ahead a
>>> little more than with a light single seater.
>
> I don't understand the physics here.
> Consider an analogy:
> when the VW-beetle came out it had a reputation of 'turning over easily',
> based on the false logic that you need less men to 'turn it over' than to
> 'pick up & turn over a bigger car'. Of course the forces while driving, that
> tended to 'turn it over' were less for a VW, but so too were the forces that
> resisted 'turn it over'.
> A heavy pendulum is 'eqivalent' to a lighter pendulum.
>
> So too for the BIG glider.
> What doesn't scale up is the pilots strength.
> Or is reynolds number significant ?
>
> == Chris Glur.
>

JJ Sinclair wrote:
> One thing I haven't seen in this discussion is the fact that the Duo's
> spoilers are not located right behind the spar. They are located quite
> a bit farther aft and thus produce mostly drag and not as much spoiled
> lift. I liken them to the H-301 Libelle spoilers that produced mostly
> dray and therefore had to be opened earlier and left out longer to get
> the same result as, say the H-201 Libelle which had true spoilers
> located at the high point of the airfoil.

My opinion is the opposite, Duo spoilers likely do an adequate of
spoiling lift, what they don't do is produce much drag. By comparison,
the trailing edge dive brakes on my Ventus caused an increase in lift
through much (if not all) of their travel, while they were producing a
tremendous amount of drag. I found it a lot easier to make steep short
landings in the Ventus than in the Duo...

Marc

The original Duo (can't speak for the new X model with the drag flap)
definitely requires more attention to energy management when landing than
your garden variety 750 pound glider. Any excess coming over the trees won't
go away by diving with full spoilers. This is a consequence of increased
weight and relatively smaller spoilers and is common to all "large" gliders.

The problem can be magnified by improperly adjusted spoilers. It is possible
that owners who have readjusted their wheel brakes have inadvertently
reduced the travel of the spoilers. Also, the Duo spoilers are heavier to
extend than smaller gliders and it takes extra muscle to hold them fully
open during the approach and flare. And as the airspeed decreases they get
heavier because the dynamics of airflow don't help hold them open.

As to the assertion that the DG-1000 has more effective air brakes than the
Duo, this is not so. While flying a DG-1000 I had the opportunity to do a
formation "test dive" comparison with a Duo. We (Tom Knauff in a Duo) got in
tight formation with me on the wing and at 65 knots pushed over while
deploying full spoilers. The two ships stayed exactly even in a descent of
500 plus feet.

Many US pilots I've noticed landing at various contest sites like to stick
the glider on the ground at speeds 20 and 30 knots above stall and then roll
thousands of feet to their trailers. This is poor preparation for the time
precise energy management is needed to get into a small outlanding field. As
the size and weight of the gliders increase the problem of stopping
magnifies, so unless you are flying a Sparrowhawk or 1-26 you should make
every landing a tail dragger touch down at an intended spot.

Karl Striedieck

"Bruce" > wrote in message
...
> Hi Chris
>
> Lets think it through then. Here is my very rusty attempt at physics -(I
> know there are experts here maybe one will bite)
>
> The bigger gliders tend to have higher aspect ratio wings. This means
> that, like the Beetle they have a polar moment challenge. The beetle would
> roll easily at speed because of a combination of aerodynamics reducing
> load on the suspension, and a high centre of gravity. Add the original
> swing axles and you have a recipe for landing on the roof.
>
> In the long wings glider you have the same issue, but symmetrical on both
> sides, the centre of mass of the wings is at a further distance from the
> roll centre of the aircraft. It thus takes more energy to achieve a
> specific rate of rotation, because you need more kinetic energy (Mass *
> distance** is against you because the wings are longer AND heavier)
> Think of two pendulums of equal mass, but different lengths. Then try it
> with the same mass but different mass distribution (Like a metronome)
> The frequency is proportional to the polar moment not the mass.
>
> I am sure the aerodynamics experts can tell you about the relative
> Reynolds numbers, but that is more a function of chord, and that is not
> radically different. The taper ratio is higher in 15m than in 26m, but the
> tips of a given generation seem to be of similar chord. This is where the
> ailerons generate the rolling force so I assume the airfoil differences
> are greater than the Reynolds number effects.
>
> What makes it necessary to stay further ahead of a 20m wingspan glider is
> inertia - stored energy. It takes longer, and / or more force to achieve
> the same deflection. Then you take into account the total mass that you
> are trying to deflect is greater and it gets worse.
>
> On the other hand I understand that 47:1 (Duo x) can get addictive.
>
> problems@gmail wrote:
>> J a c k wrote:
>>>> I think the Duo's airbrakes are better than many people think. The Duo
>>>> is a big heavy glider with lots of inertia. It doesn't like to change
>>>> direction quickly. That includes its behavior on sudden airbrake
>>>> deployment. You don't get a lot of sink right away.
>>>>
>>>> My first reaction was that the airbrakes were weak but a little more
>>>> experience showed me that with a little patience, the brakes took
>>>> effect and produced a respectable decent rate. The Duo just makes you
>>>> plan ahead a little more than with a light single seater.
>>
>> I don't understand the physics here.
>> Consider an analogy:
>> when the VW-beetle came out it had a reputation of 'turning over
>> easily',
>> based on the false logic that you need less men to 'turn it over' than to
>> 'pick up & turn over a bigger car'. Of course the forces while driving,
>> that
>> tended to 'turn it over' were less for a VW, but so too were the forces
>> that
>> resisted 'turn it over'.
>> A heavy pendulum is 'eqivalent' to a lighter pendulum.
>>
>> So too for the BIG glider.
>> What doesn't scale up is the pilots strength.
>> Or is reynolds number significant ?
>>
>> == Chris Glur.
>>

Karl Striedieck wrote:

> As to the assertion that the DG-1000 has more effective air brakes than the
> Duo, this is not so. While flying a DG-1000 I had the opportunity to do a
> formation "test dive" comparison with a Duo. We (Tom Knauff in a Duo) got in

I've never compared the two side by side. But fact is that the original
Duo is not certified for aerobatics, according to the SH homepage due to
the poor dive brakes, while the DG1000 is, as well as the new Duo X. So
yes, it seems there is a difference in air brake effectiveness.

Karl Striedieck wrote:
> The original Duo (can't speak for the new X model with the drag flap)
> definitely requires more attention to energy management when landing than
> your garden variety 750 pound glider. Any excess coming over the trees won't
> go away by diving with full spoilers. This is a consequence of increased
> weight and relatively smaller spoilers and is common to all "large" gliders.
>
> The problem can be magnified by improperly adjusted spoilers. It is possible
> that owners who have readjusted their wheel brakes have inadvertently
> reduced the travel of the spoilers. Also, the Duo spoilers are heavier to
> extend than smaller gliders and it takes extra muscle to hold them fully
> open during the approach and flare. And as the airspeed decreases they get
> heavier because the dynamics of airflow don't help hold them open.
>
> As to the assertion that the DG-1000 has more effective air brakes than the
> Duo, this is not so. While flying a DG-1000 I had the opportunity to do a
> formation "test dive" comparison with a Duo. We (Tom Knauff in a Duo) got in
> tight formation with me on the wing and at 65 knots pushed over while
> deploying full spoilers. The two ships stayed exactly even in a descent of
> 500 plus feet.
>
> Many US pilots I've noticed landing at various contest sites like to stick
> the glider on the ground at speeds 20 and 30 knots above stall and then roll
> thousands of feet to their trailers. This is poor preparation for the time
> precise energy management is needed to get into a small outlanding field. As
> the size and weight of the gliders increase the problem of stopping
> magnifies, so unless you are flying a Sparrowhawk or 1-26 you should make
> every landing a tail dragger touch down at an intended spot.
>
> Karl Striedieck

Great info on the comparison, and excellent advice on the landings. I
couldn't agree more. Pick a spot and grade yourself on each landing as
to how close you came to sticking that spot.

On Oct 31, 4:16 pm, Bruce > wrote:
> Hi Chris
>
> Lets think it through then. Here is my very rusty attempt at physics -(I know
> there are experts here maybe one will bite)
>
> The bigger gliders tend to have higher aspect ratio wings. This means that, like
> the Beetle they have a polar moment challenge. The beetle would roll easily at
> speed because of a combination of aerodynamics reducing load on the suspension,
> and a high centre of gravity. Add the original swing axles and you have a recipe
> for landing on the roof.
>
> In the long wings glider you have the same issue, but symmetrical on both sides,
> the centre of mass of the wings is at a further distance from the roll centre of
> the aircraft. It thus takes more energy to achieve a specific rate of rotation,
> because you need more kinetic energy (Mass * distance** is against you because
> the wings are longer AND heavier)
> Think of two pendulums of equal mass, but different lengths. Then try it with
> the same mass but different mass distribution (Like a metronome)
> The frequency is proportional to the polar moment not the mass.
>
> I am sure the aerodynamics experts can tell you about the relative Reynolds
> numbers, but that is more a function of chord, and that is not radically
> different. The taper ratio is higher in 15m than in 26m, but the tips of a given
> generation seem to be of similar chord. This is where the ailerons generate the
> rolling force so I assume the airfoil differences are greater than the Reynolds
> number effects.
>
> What makes it necessary to stay further ahead of a 20m wingspan glider is
> inertia - stored energy. It takes longer, and / or more force to achieve the
> same deflection. Then you take into account the total mass that you are trying
> to deflect is greater and it gets worse.
>
> On the other hand I understand that 47:1 (Duo x) can get addictive.
>
> problems@gmail wrote:
> > J a c k wrote:
> >>> I think the Duo's airbrakes are better than many people think. The Duo is a
> >>> big heavy glider with lots of inertia. It doesn't like to change direction
> >>> quickly. That includes its behavior on sudden airbrake deployment. You
> >>> don't get a lot of sink right away.
>
> >>> My first reaction was that the airbrakes were weak but a little more
> >>> experience showed me that with a little patience, the brakes took effect and
> >>> produced a respectable decent rate. The Duo just makes you plan ahead a
> >>> little more than with a light single seater.
>
> > I don't understand the physics here.
> > Consider an analogy:
> > when the VW-beetle came out it had a reputation of 'turning over easily',
> > based on the false logic that you need less men to 'turn it over' than to
> > 'pick up & turn over a bigger car'. Of course the forces while driving, that
> > tended to 'turn it over' were less for a VW, but so too were the forces that
> > resisted 'turn it over'.
> > A heavy pendulum is 'eqivalent' to a lighter pendulum.
>
> > So too for the BIG glider.
> > What doesn't scale up is the pilots strength.
> > Or is reynolds number significant ?
>
> > == Chris Glur.

Guys, if your high-school physics teacher catches you,
you're in for a dope-slap. All of yuse. Really now...

John,

Can you refer me to the SH webpage regarding the spoiler/acro issue? All I
can find on the current German version is the Duo X.

My flight manual says acrobatics are not allowed but it doesn't say anything
about "poor dive brakes" being the reason. The manual does say that the max
g loading with the spoilers deployed is reduced to 3.5. This is common for
most gliders because of the concentration of bending loads at the outboard
end of the spoilers, magnified during high g pull-ups.

Although it is purely speculation on my part, I suspect the no-acro
limitation is more a matter of the reality that poorly executed maneuvers
can lead to unintended dives, overspeed and overstress if spoilers are
deployed in a panic. I'd guess S/H is trying to stay ahead of the lawyers
rather than any structural or strength issue compared to DG.

As to your statement that the no-acro limitation means more effective speed
brakes, actual in-flight tests prove otherwise. Tom Knauff will remember our
stand-on-the-pedals dive test at the 2004 Seniors contest. Check with him.

Karl Striedieck


"John Smith" > wrote in message
. ..
> Karl Striedieck wrote:
>
>> As to the assertion that the DG-1000 has more effective air brakes than
>> the Duo, this is not so. While flying a DG-1000 I had the opportunity to
>> do a formation "test dive" comparison with a Duo. We (Tom Knauff in a
>> Duo) got in
>
> I've never compared the two side by side. But fact is that the original
> Duo is not certified for aerobatics, according to the SH homepage due to
> the poor dive brakes, while the DG1000 is, as well as the new Duo X. So
> yes, it seems there is a difference in air brake effectiveness.

Marc Ramsey wrote:
> My opinion is the opposite, Duo spoilers likely do an adequate of
> spoiling lift, what they don't do is produce much drag.

The irony is wonderful: pilots are ocasionally chastised for saying
"spoilers" when what they "really mean" is (Schmepp-Hirth) airbrakes.
And now we have a Schmepp-Hirth glider equipped with those airbrakes
that really deserve to be called "spoilers"!

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Hi Karl

The Duo passed the same JAR - now EASA certification that the DG1000 etc. did.
That means they have to limit the speed to below Vne in a relatively shallow
dive. (30 degrees)
So you are right, they will exhibit very similar performance in a dive test. It
is possible the rearward location on the duo results in the airbrake becoming
less effective in the flare, but I doubt it.

The no aerobatics certification appears to be simply a liability limitation.
Apparently the Duo will loop and spin as well as any other high performance two
seater. Which is to say, what's the point - the glider can do it, but if you
want to do aerobatics, get a different aircraft.
The DG method of shortening the wingspan makes some sense, because it improves
the aerobatic handling. But there are compromises.

Still enjoying your Duo?

Bruce

Karl Striedieck wrote:
> John,
>
> Can you refer me to the SH webpage regarding the spoiler/acro issue? All I
> can find on the current German version is the Duo X.
>
> My flight manual says acrobatics are not allowed but it doesn't say anything
> about "poor dive brakes" being the reason. The manual does say that the max
> g loading with the spoilers deployed is reduced to 3.5. This is common for
> most gliders because of the concentration of bending loads at the outboard
> end of the spoilers, magnified during high g pull-ups.
>
> Although it is purely speculation on my part, I suspect the no-acro
> limitation is more a matter of the reality that poorly executed maneuvers
> can lead to unintended dives, overspeed and overstress if spoilers are
> deployed in a panic. I'd guess S/H is trying to stay ahead of the lawyers
> rather than any structural or strength issue compared to DG.
>
> As to your statement that the no-acro limitation means more effective speed
> brakes, actual in-flight tests prove otherwise. Tom Knauff will remember our
> stand-on-the-pedals dive test at the 2004 Seniors contest. Check with him.
>
> Karl Striedieck
>
>
> "John Smith" > wrote in message
> . ..
>> Karl Striedieck wrote:
>>
>>> As to the assertion that the DG-1000 has more effective air brakes than
>>> the Duo, this is not so. While flying a DG-1000 I had the opportunity to
>>> do a formation "test dive" comparison with a Duo. We (Tom Knauff in a
>>> Duo) got in
>> I've never compared the two side by side. But fact is that the original
>> Duo is not certified for aerobatics, according to the SH homepage due to
>> the poor dive brakes, while the DG1000 is, as well as the new Duo X. So
>> yes, it seems there is a difference in air brake effectiveness.
>
>

Bruce wrote:

> The Duo passed the same JAR - now EASA certification that the DG1000
> etc. did.
> That means they have to limit the speed to below Vne in a relatively
> shallow dive. (30 degrees)
....
> The no aerobatics certification appears to be simply a liability
> limitation.

No. JAR 22 requires 30 degrees for all liders, but 45 degrees to be
certified for aerobatics and cloud flying.

Karl Striedieck wrote:

> Can you refer me to the SH webpage regarding the spoiler/acro issue? All I
> can find on the current German version is the Duo X.

http://www.schempp-hirth.com/index.php?id=130&L=1

"Duo Discus XL becomes certified for simple aerobatics!
The improved effectiveness of the airbrake system makes it now possible
for us to apply the approval for simple aerobatics including spinning."

John,

Thanks for the steer. I'd appreciate some other information if you have the
time.

Is the 20 meter DG-1000 authorized for acro? If it is I'm curious about the
reason. Both ships were designed to meet JAR standards regarding strength
and dive brake performance.

Although the 20 meter DG-1000 and the original Duo have identical speed
brake (spoiler) affectivity, I would love to have a Duo X when it comes to
off field landings, as it is much better than the other two. With 95% of my
flying being in a contest environment the exposure to "rural visitations,"
as Gren Siebels called them, is high. However, the extra $45K added to the
price tag by the sagging Dollar since I bought mine cancels that dream.

Karl Striedieck


"John Smith" > wrote in message
...
> Karl Striedieck wrote:
>
>> Can you refer me to the SH webpage regarding the spoiler/acro issue? All
>> I can find on the current German version is the Duo X.
>
> http://www.schempp-hirth.com/index.php?id=130&L=1
>
> "Duo Discus XL becomes certified for simple aerobatics!
> The improved effectiveness of the airbrake system makes it now possible
> for us to apply the approval for simple aerobatics including spinning."

Karl Striedieck wrote:

> Is the 20 meter DG-1000 authorized for acro?

With 20m it's authorized for "basic" acro, which means Loops, Turns and
erect Spins. No rolls and no negative g.

With 18m it's authorized for full aerobatics.

> If it is I'm curious about the
> reason. Both ships were designed to meet JAR standards regarding strength
> and dive brake performance.

Because the dive brakes are *not* of equal strenght. I've never compared
side by side, but the DG1000 definitely allows for a much more sloppy
approach. (Not that I would advocate sloppy flying!) I've read that you
compared them and think both are the same, I definitely don't share your
opinion.

Just for interest - lifted from the SH website news
section 25/10/2007:

'Duo Discus XL becomes certified for simple aerobatics!

The improved effectiveness of the airbrake system makes
it now possible for us to apply the approval for simple
aerobatics including spinning.'

John Galloway




At 14:01 01 November 2007, John Smith wrote:
>Karl Striedieck wrote:
>
>> Is the 20 meter DG-1000 authorized for acro?
>
>With 20m it's authorized for 'basic' acro, which means
>Loops, Turns and
>erect Spins. No rolls and no negative g.
>
>With 18m it's authorized for full aerobatics.
>
>> If it is I'm curious about the
>> reason. Both ships were designed to meet JAR standards
>>regarding strength
>> and dive brake performance.
>
>Because the dive brakes are *not* of equal strenght.
>I've never compared
>side by side, but the DG1000 definitely allows for
>a much more sloppy
>approach. (Not that I would advocate sloppy flying!)
>I've read that you
>compared them and think both are the same, I definitely
>don't share your
>opinion.
>

On Nov 1, 6:56 am, John Smith > wrote:
> Karl Striedieck wrote:
> > Is the 20 meter DG-1000 authorized for acro?
>
> With 20m it's authorized for "basic" acro, which means Loops, Turns and
> erect Spins. No rolls and no negative g.
>
> With 18m it's authorized for full aerobatics.
>
> > If it is I'm curious about the
> > reason. Both ships were designed to meet JAR standards regarding strength
> > and dive brake performance.
>
> Because the dive brakes are *not* of equal strenght. I've never compared
> side by side, but the DG1000 definitely allows for a much more sloppy
> approach. (Not that I would advocate sloppy flying!) I've read that you
> compared them and think both are the same, I definitely don't share your
> opinion.

Karl's side by side measurement is fascinating, but not what I would
expect.

I've got about 40-50 hours each in DG-1000S and Duo Discus and the
DG-1000S seems much more tolerant to sloppy handling on approach,
seems to wash off energy much more effectively with spoilers than the
Duo Discus and have less run out in ground effect. So why is this,
more effective drag (not lift spoiling) vs. speed in the DG-1000S? I
can't explain it but I definitely believe it is true. Couple this with
a more forgiving undercarriage and landings in the DG-1000S seem much
more tolerant of sloppiness than the Duo. This is not a slam against
the Duo, I like both gliders. I'll give the Duo the benefit in
handling, lighter aileron forces and very nice slow speed behavior as
it floats around a thermal (you can hear that inner wing rumble and
she just floats around).

BTW out of date now with the Duo-X but Karl did write up a comparison
of the Duo and DG-1000S in the June 2003 SSA Soaring magazine.

Since this topic is already all over the place - one thing I see in
the Duo-X collateral is Schemp Hirth still promote the light tail
weight and therefore easier ground handling (I'm sure aimed at the
DG-1000S). I wish they'd actually make the tail a little heavier to
help reduce those little tail raising surprises under brake - not that
I've ever done this but I've seen others do it :-) I suspect that is
a major change in moving the U/C more forward, but with adding the U/C
springs, and later stretched cockpit this is one thing I'd hoped they
would have tweaked as well. Anybody with Duo-X experience - is the
tail at least a little heavier?

Regards


Darryl

John,

The Duo Tom Knauff was flying when we did our full boards dive off was a
turbo version and thus heavier than a non-motorized ship. The DG-1000 I was
flying had heavier pilots, so the payload was about the same. We agreed to
this test before task opening on a day we had some extra time, because this
notion that the Duo had inferior speed brakes had been floating around for
some time and I wanted to see if it held any water. I joined up on Tom's
right wing, less than a span away, and he pushed over, deploying full brakes
and pushing the speed up to 80 knots. In this stabilized condition I had
full brakes deployed in the 1000 and did not fall back as one might expect
of a ship with better braking.

As to the matter of tail weights, wheel brakes and gear configuration there
are compromises with both approaches (long and short main gear). The old
Duo's short gear was simpler, lighter and farther aft. This makes for easier
ground handling but requires a nose wheel to handle max braking. The longer
gear of the Duo X and DG 1000 keeps the gear doors cleaner, but is more
likely to go on the nose if the brake is good.

Speaking of wheel brake effectiveness, I've spent more time adjusting,
bleeding, modifying and cursing the Duo brake than all other maintenance
matters combined. Maybe my expectations are too high after years of flawless
performance from Schleicher's Cleveland disc brake systems.

Karl Striedieck


"John Smith" > wrote in message
...
> Karl Striedieck wrote:
>
>> Is the 20 meter DG-1000 authorized for acro?
>
> With 20m it's authorized for "basic" acro, which means Loops, Turns and
> erect Spins. No rolls and no negative g.
>
> With 18m it's authorized for full aerobatics.
>
>> If it is I'm curious about the reason. Both ships were designed to meet
>> JAR standards regarding strength and dive brake performance.
>
> Because the dive brakes are *not* of equal strenght. I've never compared
> side by side, but the DG1000 definitely allows for a much more sloppy
> approach. (Not that I would advocate sloppy flying!) I've read that you
> compared them and think both are the same, I definitely don't share your
> opinion.

I have some 300 hours in a Duo, and my experience is
that the Duo's brakes are more effective the faster
you fly, compared with other gliders. Hence at the
80 knots used in the test that Tom carried out I would
expect that the brakes would work well. It is at a
55 knot approach speed that the brakes are not very
effective. My technique is that if I need to lose height,
I put the speed up to at least 65 knots. This means
a longer 'float', if the speeed is not reduced, but
in general when doing a field landing the higher speed
would mean that the approach could be made much closer
to any hedge or other obstruction. This is a fundamentally
different philosophy, from the suggestion that approaches
in the Duo must be made at a constant slow speed. At 01:42 02 November 2007, Karl Striedieck wrote:>John,>>The Duo Tom Knauff was flying when we did our full
>boards dive off was a >turbo version and thus heavier than a non-motorized
>ship. The DG-1000 I was >flying had heavier pilots, so the payload was about
>the same. We agreed to >this test before task opening on a day we had some
>extra time, because this >notion that the Duo had inferior speed brakes had been
>floating around for >some time and I wanted to see if it held any water.
>I joined up on Tom's >right wing, less than a span away, and he pushed over,
>deploying full brakes >and pushing the speed up to 80 knots. In this stabilized
>condition I had >full brakes deployed in the 1000 and did not fall back
>as one might expect >of a ship with better braking.>>As to the matter of tail weights, wheel brakes and
>gear configuration there >are compromises with both approaches (long and short
>main gear). The old >Duo's short gear was simpler, lighter and farther aft.
>This makes for easier >ground handling but requires a nose wheel to handle
>max braking. The longer >gear of the Duo X and DG 1000 keeps the gear doors
>cleaner, but is more >likely to go on the nose if the brake is good.>>Speaking of wheel brake effectiveness, I've spent more
>time adjusting, >bleeding, modifying and cursing the Duo brake than
>all other maintenance >matters combined. Maybe my expectations are too high
>after years of flawless >performance from Schleicher's Cleveland disc brake
>systems.>>Karl Striedieck>>>'John Smith' wrote in message ...>> Karl Striedieck wrote:>>>>> Is the 20 meter DG-1000 authorized for acro?>>>> With 20m it's authorized for 'basic' acro, which means
>>Loops, Turns and >> erect Spins. No rolls and no negative g.>>>> With 18m it's authorized for full aerobatics.>>>>> If it is I'm curious about the reason. Both ships
>>>were designed to meet >>> JAR standards regarding strength and dive brake performance.>>>> Because the dive brakes are *not* of equal strenght.
>>I've never compared >> side by side, but the DG1000 definitely allows for
>>a much more sloppy >> approach. (Not that I would advocate sloppy flying!)
>>I've read that you >> compared them and think both are the same, I definitely
>>don't share your >> opinion. >>>

problems@gmail wrote:

> J a c k wrote:

>>> I think the Duo's airbrakes are better than many people think. The Duo is a
>>> big heavy glider with lots of inertia. It doesn't like to change direction
>>> quickly. That includes its behavior on sudden airbrake deployment. You
>>> don't get a lot of sink right away.
>>>
>>> My first reaction was that the airbrakes were weak but a little more
>>> experience showed me that with a little patience, the brakes took effect and
>>> produced a respectable decent rate. The Duo just makes you plan ahead a
>>> little more than with a light single seater.


No, that was another to whom I was replying. Use care with editing, please.


Jack

Thanks John

I have a copy of JAR22, but did not read it well enough obviously. From other
posts it appears that Schempp have now decided to apply for the certification.

Since they have only just started building the first XLs I suppose we will have
to wait a while.

We will see how it flies in June 2008 I guess.

John Smith wrote:
> Bruce wrote:
>
>> The Duo passed the same JAR - now EASA certification that the DG1000
>> etc. did.
>> That means they have to limit the speed to below Vne in a relatively
>> shallow dive. (30 degrees)
> ...
>> The no aerobatics certification appears to be simply a liability
>> limitation.
>
> No. JAR 22 requires 30 degrees for all liders, but 45 degrees to be
> certified for aerobatics and cloud flying.