Polar with spoilers extended?

On Oct 22, 2:57 pm, wrote:
On Oct 21, 11:13 am, Tim Taylor wrote:



On Oct 21, 10:50 am, " wrote:

Tim,
I have flown with you, why do you want to know this information? You
take off, fly far and fast and land when your glider touches the
ground. I don't ever remember you "using" spoilers...

Tom,

LOL, thanks. It is purely an academic exercise from a safety
discussion we had about what are the best steps to follow if you are
high on final. I am trying to look at the difference between several
suggested techniques if full spoilers are not enough.

My list of preferences is:
1. Full spoilers
2. add forward slip
3. add "S" turns

I have used the technique of slowing down to minimize forward speed,
increase sink and decrease glide angle. Others have suggested
increasing speed to increase drag. I am not a big fan of this
technique because I feel it minimizes options for the pilot and is
susceptible to pilot error that can end up in over shooting the LZ.
Last years article in soaring I believe confirms my feeling that this
is a technique that should not be held up as one of the primary
techniques that should be used. I am working on developing models to
asses each in terms of effectiveness, time required, safety and
options left to the pilot.

Tim

If you are THAT much too high, wouldn't it also be prudent to consider
a large 360? It may not be pretty, but let's face it, if you have
turned final and just THEN realized you're way too high, you've
already lost all your style points.

I only did a 360 once (my first solo landing in a high-performance
glass ship). I lost sight of the runway turning and ended up in a
worse position than if I had just continued.

These days, if I find myself a bit high, I apply full spoilers and
increase speed. If that's not enough, I add slip. Drag goes up at
least as the square of speed. I've never had a problem slowing down.

Mike

Mike the Strike wrote:
These days, if I find myself a bit high, I apply full spoilers and
increase speed. If that's not enough, I add slip. Drag goes up at
least as the square of speed. I've never had a problem slowing down.

For whatever reason (I don't really want to start that flame war again,
although I think the mods to the DDX quietly prove the point), I've
found that the Duo Discus does not take kindly to excessive speed on
approach. There is no elegant way to bleed off the excess energy, you
end up either floating down the runway, or forcing it down hot and
jamming on the brakes. It is best to maintain a proper approach speed
with full dive brakes and slip or S-turn as needed. I've heard that the
Libelle behaves in a similar fashion...

Marc

On Oct 22, 4:46 pm, Marc Ramsey wrote:
Mike the Strike wrote:
These days, if I find myself a bit high, I apply full spoilers and
increase speed. If that's not enough, I add slip. Drag goes up at
least as the square of speed. I've never had a problem slowing down.

For whatever reason (I don't really want to start that flame war again,
although I think the mods to the DDX quietly prove the point), I've
found that the Duo Discus does not take kindly to excessive speed on
approach. There is no elegant way to bleed off the excess energy, you
end up either floating down the runway, or forcing it down hot and
jamming on the brakes. It is best to maintain a proper approach speed
with full dive brakes and slip or S-turn as needed. I've heard that the
Libelle behaves in a similar fashion...

Marc

I should add I am a lot more careful about setting up my approach in
my Discus 2 than I was in my ASW-20, which was equipped with the
"Jesus" flap. I set up my altitude on the downwind leg, and that's
where I'll use the dive brakes with higher speed. I like to be at the
proper altitude when I turn base so that I can get the speed right on
final.

I think we may both agree that you don't want to dive at the runway at
the last moment.

Mike

Marc Ramsey wrote:
I've
found that the Duo Discus does not take kindly to excessive speed on
approach. There is no elegant way to bleed off the excess energy, you
end up either floating down the runway, or forcing it down hot and
jamming on the brakes. It is best to maintain a proper approach speed
with full dive brakes and slip or S-turn as needed. I've heard that the
Libelle behaves in a similar fashion...

I've not tried that in my Libelle on finals (a full brake slip has
always fixed that situation very nicely to date - like hitting DOWN in a
lift) but I have tried it higher, when I wanted to get down quickly to
circuit height. Popping the brakes at 70+ kts with the wheel down gave
me a noticeable boost forward against the straps and I found I had to
push the nose down quite a bit further than I expected to maintain 70.
This is in an H201 with upper and lower surface brakes, not a B series:
at this speed a Libelle's brakes aren't as wimpy as many folks say they are.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

On Oct 22, 12:46 pm, Marc Ramsey wrote:
I've found that the Duo Discus does not take kindly to excessive speed on
approach. There is no elegant way to bleed off the excess energy, you
end up either floating down the runway, or forcing it down hot and
jamming on the brakes. It is best to maintain a proper approach speed
with full dive brakes and slip or S-turn as needed. I've heard that the
Libelle behaves in a similar fashion...

Marc

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.

So, people try to "tighten" the wheelbrake, and end up
just restricting the spoiler travel. And half the time the
wheelbrake still doesn't work.

Anybody have the measurement from wing surface
to spoiler cap, spoiler fully extended, on a properly
adjusted Duo so folks can do a quick check ? I'll
try get one of my partners to measure ours next
weekend...

And yes, I've seen this on Duo's in a number of
different locations...

Hope this helps,
Best Regards, Dave "YO"

PS: Yes, our Duo has effective spoilers, and its
the original model. But we don't trust the brake !

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

"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

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

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.

Bill Daniels 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.


In other words, the Duo "airbrakes" are not very effective. Lots of big,
heavy, fast aircraft do have effective spoilers/speedbrakes/"airbrakes",
or whatever you want to call them, that make the desired changes in
speed/rate of descent promptly.

Every car's acceleration from 35 to 65 for merging into Interstate
highway traffic is adequate--if you are willing to wait for it.

I learned to "plan ahead" when passing on two lane roads in my VW
Beetles and early un-blown Corvairs. I know what planning ahead means
and that is not "performance" as we like to think of it. The same goes
for sailplane spoilers whose effects are not prompt, and rudders which
are not effective enough to allow a good steep high descent-rate slip.


Jack