Duo Dive-brakes ( Polar with spoilers extended?)

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.

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.

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.

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.

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.

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.