Polar with spoilers extended?

There are other big heavier gliders with lots of inertia, and they react
very well and immediately to the deployment of airbreaks.
Those on the original DuoDiscus are just a very bad design. But, as Marc
pointed out, a sideslip works well AND gets you a visual on the airfield
from the back seat (the second very bad design glitch of the Duo).

Bert

"Bill Daniels" bildan@comcast-dot-net wrote in message 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.

Bill Daniels

Certainly there are some gliders with inadequate divebrakes.
A modification was applied to the Cirrus. I've not
flown a Duo; perhaps it needs a mod; thin airfoils
are not conducive to installing wide vertical plates.

At 02:12 23 October 2007, Marc Ramsey wrote:
Nyal Williams wrote:
I first learned it in Minden and then refined it in
Cal City.

What the objecters have not realized is just how fast
you can bleed off tons of excess speed by lifting
the
nose to the horizon with full spoilers out.

The objectors are pointing that there are some gliders
whose spoilers
don't produce quite enough drag to manage this maneuver
effectively. In
a glider that has effective spoilers (like a Ventus
B) it's a blast.
But, in my experience (which were usually at 8000+
foot density
altitude), a Duo will accelerate rather quickly in
a dive with full
spoilers, then take you halfway down the runway while
you bleed off 15
or 20 knots of excess speed, even out of ground effect.
If you bleed it
off more quickly, you're going up. I found a slipping
turn to final
that is held for as long as needed to be far more effective.
Your
mileage may vary...

Marc

as an ex Duo owner I agree with Dave Nadler and Bill
Daniels; the Duo airbrakes are better than their reputation:

The manual says the give a glide angle of 6.7:1 (which
fits with my measurements of 800fpm descent rate) at
approach speed which isn't barn door but should be
adequate. My D2cT manual quotes the same approach
glide angle (I observe the same sink rate of 800fpm)
- and reviewers assess the D2c airbrakes as very good.
I made the same observation as Bill about the Duo
brakes taking a couple of seconds for the drag to build
up - I thought it had something to do with a more turbulent
airflow as the trim changes nose down with the brakes
deployed(??)

The Duo airbrakes need a very strong pull to fully
open them - but this is aided on later ones by a mod
to the control linkage (also available as a simple
retrofit)

Also, our Duo was delivered with the airbrake lever
actuated hydraulic wheel brake picking up well before
full airbrake and I initially found it almost impossible
to pull full airbrake - it is easy to adjust the wheelbrake
and this, along with the linkage mod, helped a lot.

However our wheel brake was so effective that if the
glider touched down on grass with the wheel brake fully
on then the wheel didn't turn and the glider bounced
as if it had hit a rock. As a result I always had to
close the airbrakes a little before touch down which
increased float.

John Galloway


At 15:18 23 October 2007, Bert Willing wrote:
There are other big heavier gliders with lots of inertia,
and they react
very well and immediately to the deployment of airbreaks.
Those on the original DuoDiscus are just a very bad
design. But, as Marc
pointed out, a sideslip works well AND gets you a visual
on the airfield
from the back seat (the second very bad design glitch
of the Duo).

Bert

'Bill Daniels' wrote in message 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.

Bill Daniels

John Galloway schrieb:

The manual says the give a glide angle of 6.7:1 (which
fits with my measurements of 800fpm descent rate) at
approach speed

Very interesting, indeed:

JAR 22.75 Descent, approach
It must be shown that the sailplane has a glide
slope not flatter than one in seven at a speed of
1·3 VS0 with air brakes extended at maximum
weight.

John Galloway wrote:
as an ex Duo owner I agree with Dave Nadler and Bill
Daniels; the Duo airbrakes are better than their reputation:

Well, clearly, not all current and former Duo owners agree. Perhaps I'm
used to gliders with very effective spoilers, including various DG
models, ASW20s, Ventus Bs, etc. But, after 200 or so hours in our Duo
(and a couple of others in the area), I'll simply say that the spoilers
were workable with proper approach planning and airspeed, and that it
remains the only glider I've ever felt the need to slip on a routine
basis...

Marc

On Oct 22, 9:12 am, Nyal Williams
Forward slip in glass gliders won't get you much descent;

The ASW-19 and ASW-28 have a huge increase in sink rate in a full
rudder slip compared with airbrakes alone. What glass gliders are
you flying that do not slip well? Can you maintain a full rudder
slip, and I mean rudder on the stop and never comes off it until you
choose to exit the slip?


Andy

Bill Daniels wrote:
"Marc Ramsey" wrote in message
. ..
wrote:
Hey Marc - The Duo spoilers are much maligned,
but often the problem is the wheelbrake.

Huh ?

Well, the wheelbrake engages at the end of the spoiler
travel. The mechanism is, well, um, even though its a
Cleveland wheel, the mechanism and hydraulics are
shall we say a bit confused.
You may be right, our Duo had a great wheelbrake (almost disconcertingly
so), but relatively poor spoilers. That's not the say they were a
problem, just that one developed slightly different techniques for
arriving in an elegant fashion. In particular, in calm conditions I
preferred long shallow finals. In hairier situations, a slipping turn to
final with full spoilers allowed excellent control over descent rate, with
the added benefit that I could actually see the runway from the back seat
;^)

I think the Duo Discus X does a great job of addressing the glidepath
control issue (imagined or not). When I win the lottery, after I order my
Antares, the DDX comes next...

Marc

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.

Bill Daniels


I've flown plenty in the Duo and while the dive brakes are not the most
powerful around, they do just fine. One is hard pressed to find a
glider that handles as well, with great performance. I wish I still had
it, and look forward to the day when I can order another Duo.

That was probably an overstatement; I meant as compared
to the HPDA. I have not flown a 19 or 28. I fly a
Discus B and a G-103 regularly, along with Blanik L-23s
for instructing. The Blaniks are the worst, and not
glass, of course. A fully locked rudder slip won't
allow much opposite aileron before it starts to turn
off course. Of course, that is not glass, (and I almost
made an anadiplosis there.)

At 20:06 23 October 2007, Andy wrote:
On Oct 22, 9:12 am, Nyal Williams
Forward slip in glass gliders won't get you much descent;

The ASW-19 and ASW-28 have a huge increase in sink
rate in a full
rudder slip compared with airbrakes alone. What glass
gliders are
you flying that do not slip well? Can you maintain
a full rudder
slip, and I mean rudder on the stop and never comes
off it until you
choose to exit the slip?


Andy

On Oct 23, 2:00 pm, Marc Ramsey wrote:
John Galloway wrote:
as an ex Duo owner I agree with Dave Nadler and Bill
Daniels; the Duo airbrakes are better than their reputation:

Well, clearly, not all current and former Duo owners agree.

My 2c: (Our club has a duo, so based on some experience.) The actual
glide angle of the duo, with full spoilers out and at a stable
approach speed, is decently steep. Looking at this angle at altitude
is instructive. The duo seems not to lose speed as quickly as other
gliders when you open the spoilers, especially in ground effect. "Too
high" really often means "too fast". I think a lot of the perception
that the duo has poor divebreakes is realy that it does not slow down
fast, rather than the actual steady state glide angle is shallow.

This all makes some aerodynamic sense. The duo is heavier than basic
trainers, and much heavier than the single seaters we are used to.
"Spoilers" work as much by "spoiling lift" as by "increasing drag",
and much of the latter is induced drag due to the gap in the lift
distribution anyway.


John Cochrane

BB wrote:
On Oct 23, 2:00 pm, Marc Ramsey wrote:
John Galloway wrote:
as an ex Duo owner I agree with Dave Nadler and Bill
Daniels; the Duo airbrakes are better than their reputation:
Well, clearly, not all current and former Duo owners agree.

My 2c: (Our club has a duo, so based on some experience.) The actual
glide angle of the duo, with full spoilers out and at a stable
approach speed, is decently steep. Looking at this angle at altitude
is instructive. The duo seems not to lose speed as quickly as other
gliders when you open the spoilers, especially in ground effect. "Too
high" really often means "too fast". I think a lot of the perception
that the duo has poor divebreakes is realy that it does not slow down
fast, rather than the actual steady state glide angle is shallow.

This all makes some aerodynamic sense. The duo is heavier than basic
trainers, and much heavier than the single seaters we are used to.
"Spoilers" work as much by "spoiling lift" as by "increasing drag",
and much of the latter is induced drag due to the gap in the lift
distribution anyway.

That's how this whole discussion got started. Someone suggested that
the best thing to do when high on final is to dive with full spoilers,
pull up above ground effect and wait for the speed to bleed off. I said
that won't work too well with a Duo, as with full spoilers it isn't all
that draggy, will accelerate relatively quickly, and bleed off speed
slowly. Others said nonsense, the Duo has wonderful spoilers. And so
on, and so on...

Marc