Polar with spoilers extended?

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

On Oct 22, 2:23 pm, Alastair Harrison
wrote:
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.

Perform the dive recovery in two steps:

Diving with full spoilers and 80-90 KIAS, do a fairly sharp roundout
at 50-60' (a wingspan, at least) above the ground. Then, while still
holding full spoilers, set up a glide angle similar to what you would
get if flying final at normal speed. Airspeed will continue to
diminish, and when you have reached the target airspeed, still
slightly above where the normal roundout would be, reduce spoilers, if
necessary, roundout and land.

Do not attempt to do the high speed roundout near the ground! Do it
in two distinct steps and all will be well. With practice, it may
appear you are doing it in a single step to a casual observer.

I don't demo this often enough to have a perfect picture in my mind
for explaining here, but I have not had any trouble talking someone
through the procedure in an ASK-21. And we do indeed end up stopping
at or before the 'normal' stopping point even though we turned final
at 800-1,000'.

-Tom

Alastair Harrison wrote:
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 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.

As Andreas points out, the maneuver we're talking about is performed
"high" at the early part of the final approach. When the glide to the
desired aim point "looks right", the glider is returned to the desired
approach speed (spoilers still fully out). The spoilers are then
retracted to about half way, and the approach is continued as you
normally would.

If you have to maintain the high speed all the way to the flare, you
were too high to use it. A slip might be better if you are "low" when
you decide full spoilers alone aren't enough.

--
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, 9:23 pm, Alastair Harrison
wrote:
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.

Once, when I was still pre-solo, with a 15kt headwind, I felt unsure
of the K13's penetration, so I deliberately turned onto finals at
about 600'
only just outside the airfield boundary. Given that its a 6000ft
landing strip,
there wasn't exactly a problem with overshoot, but there would have
been a walk.

However the instructor told me to get to 75knots and apply full
airbrake.
It felt like a 45degree dive into the ground - somewhat exhilarating.
I got serious groundrush at (I guess) about 100ft and consciously
started to pull out the dive. Very quickly I was satisfied that I
wasn't
going to hit the deck, and so returned to the roundout and pleasantly
short landing.

Overall the speed was always more than adequate for the windshear
conditions, and the plane lost height and stopped remarkably (to me)
quickly. During the debrief neither the instructor nor I was
concerned about my reactions during that manoeuver. There was
more discussion about how much deeper it would have been
sensible for me to go in K13/15kt.

Would I recommend it? Of course not!
Would I do it again? Yes, if it seemed that was the only course
of action, or if I was more skilled.

Tom Gardner wrote:


Once, when I was still pre-solo, with a 15kt headwind, I felt unsure
of the K13's penetration, so I deliberately turned onto finals at
about 600'
only just outside the airfield boundary. Given that its a 6000ft
landing strip,
there wasn't exactly a problem with overshoot, but there would have
been a walk.

However the instructor told me to get to 75knots and apply full
airbrake.
It felt like a 45degree dive into the ground - somewhat exhilarating.
I got serious groundrush at (I guess) about 100ft and consciously
started to pull out the dive. Very quickly I was satisfied that I
wasn't
going to hit the deck, and so returned to the roundout and pleasantly
short landing.

Overall the speed was always more than adequate for the windshear
conditions, and the plane lost height and stopped remarkably (to me)
quickly. During the debrief neither the instructor nor I was
concerned about my reactions during that manoeuver. There was
more discussion about how much deeper it would have been
sensible for me to go in K13/15kt.

Would I recommend it? Of course not!
Would I do it again? Yes, if it seemed that was the only course
of action, or if I was more skilled.


Hello Tom. To be sure, if you ever need to be doing this at Aston Down
then you've got something very wrong :-)

The first demo given to me was at the more extreme end of what's
possible, and I think there may have been an element of willy waving on
the part of the chap demonstrating (what with the hop over the wall).
And I take the point that it's not usually necessary to finish the
manoeuvre at ground level. I was reintroduced to the technique in the
context of winch launch failures at awkward heights and positions in
short fields. Not enough height to do a 360, and marginally high for
landing ahead. So everything had to be done pretty accurately.

Alastair