Polar with spoilers extended?

On Oct 22, 10:12 am, Nyal Williams
wrote:
Frightening! That you would slow down to decrease
forward motion. What happens with downdrafts or wind
shear after you have given up the option for altitude
that speed gives you.

snip

Frightening? Really? It actually works very well with a bit of head
wind. Backcountry power pilots occasionally use this technique as
well.

It could be "Frightening" on a normal approach but remember the
context. A Downdraft or Windshear would be welcomed as the whole point
is to lose altitude. It does requires some expertise in slow flight
and stall awareness. But then glider pilots or at least soaring pilots
are supposed to be the experts at slow flight. Once you get down
close to a normal approach angle simply accelerate (which will bleed
off some more altitude) to your normal approach speed and fly the
remaining part of the approach normally. In fact it is necessary that
at about 200 feet AGL or higher that you do accelerate to a normal
approach speed so that you will have enough energy to flare with.

I would strongly recommend practicing it with an instructor and in the
specific airplane before having to use it. Usually with gliders there
are other, as good, or better options to this technique.



Brian

Tim Taylor wrote:

[....]

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.


Increasing speed has its uses, and it has the distinct advantage of
being able to get out of rather more easily and safely than slowing
down, when you find you have over-done it. Of course there is the
concern that those who find themselves needing a lot of it may not be
the persons who'll know promptly when they've had enough, nor how best
to handle having too much--but there are ways to avoid being one of them.

The S-turns can be helpful when one has both the horizontal and
vertical space for them, if we arrange to be finished with them before
we are low, and ALWAYS watch our drift, as it changes with altitude and
airspeed changes--both IAS and GS--throughout the final approach. I
often see people failing to correct for drift as soon as they should,
which only leads to further complications.

I've found it useful to practice with increasing amounts of variation
from the basic final approach airspeed, both plus and minus, in order to
get to know what works with my glider in the relatively controlled
environment of my home field. This is at least a start in preparing for
the inevitable off-field or strange-field approach and landing, not to
mention the unheralded/unheeded arrival of geese, Cessnas, Boeings, or
skydivers in the pattern.

I can only advise any rated pilot to try each of those techniques
under benign conditions, working in small increments away from the
nominal speeds and configurations, changing one variable on each
approach. Pretty much what you learned to do in high-school science
labs. It may not be rocket science, but please do have a plan on every
approach--just as you do on every departure--to include touchdown and
stop points. And when you are on the ground make sure you know why the
plan worked, or why it did not--before you take the next step.

Thanks for the opportunity to harangue the assemblage. I'll try to
remember to impose some limits on this sort of thing next time, possibly.


Jack

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

Brian wrote:

Frightening? Really? It actually works very well with a bit of head
wind. Backcountry power pilots occasionally use this technique as
well.

It's a completely different thing in a power plane. (Although I wouldn't
recommend it with power planes, either.)

A short look at a typical glider polar is all that is needed to
understand why your "technique" is a no-no. If you continue using it,
then it's only a question of time that we'll hear about you in the news.

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

On Oct 22, 11:38 pm, Alastair Harrison
wrote:
Hello Tom. To be sure, if you ever need to be doing this at Aston Down
then you've got something very wrong :-)

Just so. It is a nice big target for cough inexperienced
/cough pilots.

And I take the point that it's not usually necessary to finish the
manoeuvre at ground level.

I can only claim instinctive reactions, not pre-planned
choreography, unfortunately.

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.

I decided not to learn at other local fields for just
that kind of reason.

Regarding being high on final, there is a place for both the full
spoiler/increased approach airspeed and the slipping technique. Just as
important as being proficient doing them is knowing how to choose the
most appropriate for the conditions. For example if the wind is strong,
the full spoiler/increased speed is generally safe because losing the
energy at the bottom of the maneuver should be no problem. If the wind
is zero or very light and/or there is a long line of gliders waiting to
launch (we land and depart at 4220 MSL on the same runway at Tehachapi)
and therefore the landing runway is shorter than normal, a slip might be
most appropriate since you get a high sink rate without adding excessive
energy to get rid of at the bottom.

As for doing a 360 in the pattern, you may need a plan B when the guys
behind you take the runway away from you.

Paul
ZZ








Dan G wrote:
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 Oct 22, 4:52 pm, Tom Gardner wrote:
And I take the point that it's not usually necessary to finish the
manoeuvre at ground level.

IMHO, it's useful to demonstrate this on final approach, but a better
place to apply it in real life would be earlier in the landing
pattern. For example huge amounts of lift on downwind, so dive off
the altitude on base.

In the US southwest, where downbursts and the associated huge sink and
sometimes lift can happen, I've found myself turning a high final
expecting 40-50 knots headwind and it's vanished. I've also
experienced huge lift on base / final as the outflow curl decided to
position itself right at the end of the runway. So these are the
cases where I might be tempted to use the dive while on final
approach.

-Tom