Polar with spoilers extended?

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

On Oct 22, 7:57 am, wrote:
On Oct 21, 11:13 am, Tim Taylor wrote:
[snip]
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.

Was this a serious comment? How many more people have to die to prove
you should not be suggesting turning away from the runway? A pilot was
killed in the Sierras in the last few years doing exactly this and we
had at least another major accident this year in the Sierras this year
with the same thing. It is on of the precursors to stall-spin
accidents, nasty scenarios like if unexpected lift cause the glider to
be high, the turn takes the glider out of lift, now you are going down
fast and pointing the wrong way. And low and the ground is coming up
at you, maybe I'll pull back more, push that foot to make the nose go
round, ugh, oh f!@#... Use S-turns, parasitic drag approaches, slips
etc. but don't turn away from the runway.

---

As for the high speed/paracitic drag approach Cindy Brinkner talked
about this at an SSA convention a few years ago. Maybe she has slides
available etc. I was suprised by the whispering amongst some people
in the audience about "ohh this is bad". I see it as a very useful
tool to have in your toolkit. I think Cindy's points were don't try it
by yourself - go take a ride with an knowledgeable instructor and that
in the hands of less experienced piltos in the right gliders this may
be a safer techqunique than slipping - I've seen pilots who have *no*
clue how to really slip to loose height, far too timid, nose just a
little off center - I have no idea if they were taught better and have
just forgotten or what.

Like Marc says the Duo tends to hold energy and makes this somewhat
less useful (but it still works, you do come down faster), but slips
work great in a Duo as compensation for not overly effective spoilers.
I was all set to demonstrate a parasitic drag approach in a Duo today
but the instructor doing the check ride thought a rope break would be
better :-(

Things are not black and white, I'd hope good pilots want to try out
different techniques, see what works best in different gliders and
situations and have the benefit of different tools at their disposal.

Darryl

I have used the high speed parasitic drag approach, and others.

First point is - no-one here has mentioned that the appropriate action depends
on the wind speed and direction.

In all cases drag increases at the square of velocity.
If you have a really low drag glider that is optimised for high speed you might
not get that high a return.
In a low performance ship the results are dramatic.

Consider being way too high on final approach in a low wing loading wood and
fabric trainer. If you are in still air, or have a tail wind then diving will
work best. Maximum drag, get close to the ground, bleed speed off.
If you have a strong headwind you can slow down and increase your angle of
decent, not rate. This is the inverse calculation of working our McCready speed
for best XC distance. Here you want to reduce the distance by flying too slowly.
One hint - you will be descending through wind gradient so leave a height +
speed reserve to compensate close to the ground.

Another technique is - if you see you are too high turning onto final, why
continue the turn. Extend the base leg a bit, make a steep 90 degree turn back
and line up. It is a sort of S turn, but more effective in that you start from
90 degrees to the landing point.

I know at least one pilot who has serious injuries from making an S turn and
losing it. So any of the approaches carries risk. We generally teach side
slipping as the preferred method, and with 6000 feet of runway - land long
rather than spin in trying to nail the threshold. Landing in a field is a
different matter.

I must agree the 360 is a bad idea. Not saying you should never do it - I did it
once to avoid conflicting traffic - but it is not advisable/comfortable to lose
sight of the runway low down. Use the appropriate one for the circumstances.

wrote:
On Oct 22, 7:57 am, wrote:
On Oct 21, 11:13 am, Tim Taylor wrote:
[snip]
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.

Was this a serious comment? How many more people have to die to prove
you should not be suggesting turning away from the runway? A pilot was
killed in the Sierras in the last few years doing exactly this and we
had at least another major accident this year in the Sierras this year
with the same thing. It is on of the precursors to stall-spin
accidents, nasty scenarios like if unexpected lift cause the glider to
be high, the turn takes the glider out of lift, now you are going down
fast and pointing the wrong way. And low and the ground is coming up
at you, maybe I'll pull back more, push that foot to make the nose go
round, ugh, oh f!@#... Use S-turns, parasitic drag approaches, slips
etc. but don't turn away from the runway.

---

As for the high speed/paracitic drag approach Cindy Brinkner talked
about this at an SSA convention a few years ago. Maybe she has slides
available etc. I was suprised by the whispering amongst some people
in the audience about "ohh this is bad". I see it as a very useful
tool to have in your toolkit. I think Cindy's points were don't try it
by yourself - go take a ride with an knowledgeable instructor and that
in the hands of less experienced piltos in the right gliders this may
be a safer techqunique than slipping - I've seen pilots who have *no*
clue how to really slip to loose height, far too timid, nose just a
little off center - I have no idea if they were taught better and have
just forgotten or what.

Like Marc says the Duo tends to hold energy and makes this somewhat
less useful (but it still works, you do come down faster), but slips
work great in a Duo as compensation for not overly effective spoilers.
I was all set to demonstrate a parasitic drag approach in a Duo today
but the instructor doing the check ride thought a rope break would be
better :-(

Things are not black and white, I'd hope good pilots want to try out
different techniques, see what works best in different gliders and
situations and have the benefit of different tools at their disposal.

Darryl

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.

I didn't think so either until Marty Eiler at Cal City demonstrated it
for me as part of a BFR. Practiced, and properly done, it can produce
an unbelievably steep angle from decision point to stopping point. Yes
you have to point the nose at the ground and look temporarily like
you'll undershoot. Definitely not for beginners, but not a maneuver to
be dismissed either.

A suggestion: I bought a copy of the condor flight simulator a while
ago, in part to explore on the ground how things like this work out.
It does let you practice and explore limits of glider abilities. You
can find out, for example, exactly how much altitude a 360 will take
in various configurations, or how much altitude you really need for a
180 back to the airport.

John Cochrane

On Oct 22, 11:30 am, BB wrote:
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.

I didn't think so either until Marty Eiler at Cal City demonstrated it
for me as part of a BFR. Practiced, and properly done, it can produce
an unbelievably steep angle from decision point to stopping point. Yes
you have to point the nose at the ground and look temporarily like
you'll undershoot. Definitely not for beginners, but not a maneuver to
be dismissed either.

A suggestion: I bought a copy of the condor flight simulator a while
ago, in part to explore on the ground how things like this work out.
It does let you practice and explore limits of glider abilities. You
can find out, for example, exactly how much altitude a 360 will take
in various configurations, or how much altitude you really need for a
180 back to the airport.

John Cochrane

Doing these tests in the actual glider (at high altitude) with a data
logger will produce reliable numbers. The simulator might or might
not reproduce the performance accurately enough.

Todd Smith
3S

BB wrote:
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.

I didn't think so either until Marty Eiler at Cal City demonstrated it
for me as part of a BFR. Practiced, and properly done, it can produce
an unbelievably steep angle from decision point to stopping point. Yes
you have to point the nose at the ground and look temporarily like
you'll undershoot. Definitely not for beginners, but not a maneuver to
be dismissed either.

I find it a very useful technique if I am high enough on final to use
it. Generally, I use it shortly after turning final as I realize I am
too high, even with full spoiler. That's when I have 500' agl or so,
which is plenty. Going from 50 knots to 70 knots (watch the flap setting
speed) doubles the rate of energy loss. When I slow down to 50 knots
again (still at full spoiler), my new "aim point" is much closer, and I
can reduce the spoilers to (ideally) about half.

If I'm "low", say less than 200', when I decide I'm too high, slipping
is my choice. I've never used S turns: if I'm high enough to make turns
on final, it's easier and safer to dive off the speed.

--
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

On Oct 22, 5:58 pm, Eric Greenwell wrote:
I find it a very useful technique if I am high enough on final to use
it. Generally, I use it shortly after turning final as I realize I am
too high, even with full spoiler. That's when I have 500' agl or so,
which is plenty. Going from 50 knots to 70 knots (watch the flap setting
speed) doubles the rate of energy loss. When I slow down to 50 knots
again (still at full spoiler), my new "aim point" is much closer, and I
can reduce the spoilers to (ideally) about half.

All this is way outside my experience, and I'm not going to attempt it
myself (though I might nobble an instructor experienced at it).
However I still have a question: do you dive and then return to normal
approach speed before rounding out, or round out at the much faster
speed? If the latter, does not the extra float in ground effect negate
the losses from extra drag in the dive, especially with a slippery
glass ship versus a draggy wood and fabric glider (such as one a pilot
might train in)?


Dan

On Mon, 22 Oct 2007 19:17:18 -0000, Dan G wrote:


However I still have a question: do you dive and then return to normal
approach speed before rounding out, or round out at the much faster
speed? If the latter, does not the extra float in ground effect negate
the losses from extra drag in the dive, especially with a slippery
glass ship versus a draggy wood and fabric glider (such as one a pilot
might train in)?

You found the problem!
The key is to be back at normal approach speed while still outside the
ground effect.
This means you need to decide about using this maneuvre while still
fairly high.

Bye
Andreas

Dan G wrote:
SNIP
However I still have a question: do you dive and then return to normal
approach speed before rounding out, or round out at the much faster
speed? If the latter, does not the extra float in ground effect negate
the losses from extra drag in the dive, especially with a slippery
glass ship versus a draggy wood and fabric glider (such as one a pilot
might train in)?
SNIP


I had this demonstrated to me by a very experienced instructor in a K13.
He had me fly a deliberately high and close in circuit until it was
clear that we'd be a long way up the field, even with full airbrake.
Then he took over and performed the 'energy dumping' manoeuvre, which
involved opening full brake and pointing the nose at the ground.

It all happened rather fast and was not unalarming, so my recollections
are not exact. However, I'm fairly sure the speed never exceeded 80kts.
Certainly the ground approached very rapidly. One moment we were in a
gross overshoot situation and the next moment I was concerned that we
might impact the ground before reaching the boundary wall. We came out
of the dive, popped over wall and settled on to the ground for one of
the shortest landings I've seen. I remember being surprised at how
quickly we lost the excess speed. Pulling out of a near-vertical dive
(at least that's what it felt like) with full airbrakes seems to scrub a
lot of energy very quickly.

I asked the instructor whether this would work in something more
slippery. He answered that it would, but of course it wouldn't be so
effective as in the K13. He even told that he had successfully
demonstrated it in a Duo, though I don't have any quantitative or
qualitative information to say how effective it was.

I was also taught this technique on a basic instructors course (in a
G103). But I'm always left thinking that it requires a high level of
skill to judge the roundout correctly. Leaving it just a second too
late would result in a rather rapid meeting with the ground. I think
I'd rather take my chances with a side slip.

Alastair