Polar with spoilers extended?

"jeplane" wrote in message
ups.com...
360 on final?

Mmhhhh.... Two things come to mind:

- What if there are traffic in the pattern?
- What if at the end of your 360, you end up too low?

I like Tim's list better, and in fact, this is what I teach with
students.

And mine too, but things don't always go according to plan. I got into a
situation as a student pilot where I did a 360 on final. It was a case where I
had a brisk tailwind on my downwind leg combined with strong lift. In spite of
full deployment of the wimpy spoilers on my 2-33, I was climbing rather than
descending in the pattern.

As a more experienced pilot, I might have ventured downwind for a few seconds
making the pattern a non-event, but as a student pilot I rejected that option
due to fear of overdoing things in the brisk wind and landing short. I could
have added slip starting early on the downwind, but didn't even think of it at
the time and that opportunity was quickly behind me. We had recently been
practicing low rope breaks, so I did the math and figured out what a 360 (2
"rope break" 180-degree turns) would cost me and went ahead and did it whilst on
final. It worked out great, but my instructor was not pleased.

Vaughn

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

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 22 Oct 2007 16:12:47 GMT, Nyal Williams
wrote:

Forward slip in glass gliders won't get you much descent;

I'm not sure about that - the glass gliders that I have tried forward
slips with usually got really huge descent rates.

A few examples:
ASK-21, G-103, ASW-24: Sideslip very effective
DG-300, DG-505: Sideslip extremely effective
AS22-2: Sideslip pretty effective






Bye
Andreas

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 had this taught to me as part of my UK Basic Instructor renewal
course/checks. It works well in a glider with good airbrakes, but not in
something like my Open Cirrus (unless, perhaps, it's a long, long
approach so that there's time to drop below glide path with full brake
and normal approach speed, then bleed off the speed and come back into
the approach funnel at the proper speed).

It's one for the experienced (and properly taught) because you need to
know what's going to happen after you round out. In, say, a Puchacz, the
brakes are so good that you get only a comparatively small increase in
float. In my Cirrus, 10kt extra with full airbarke will far more than
double the float at a height where there is nothing you can do about it
except hang on. Libelles are known to be similar, and from a previous
poster the Duo Discus as well. Fortunately, those who fly gliders with
"weak" airbrakes soon learn about approach speed control ....

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

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

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 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