Another stall spin

Am Montag, 3. September 2012 01:38:50 UTC+2 schrieb unkown:
Am Donnerstag, 30. August 2012 22:13:31 UTC+2 schrieb (unbekannt):



I like Bruno and his videos, but some of what he does and shows do not reflect examples of how we should all fly. This is such an example.



So- what does Crabby UH say he did wrong?



1- Obviously exceeded the critical angle of attack of the inboard wing- gust likely a factor- could happen to any of us, and does.



2- As the wing starts to drop, adds top aileron, obviously as an automatic and likely habitual reaction. This has the effect of increasing the angle of attack on the most critical portion of the wing at exactly the wrong time.



3- No obvious use of opposite rudder.



4- No forward stick to reduce angle of attack, in fact it appears the stick is positively held back.



The dumping of flaps seems to be well practiced in recovering from this maneuver- I wonder who taught him this.





When I have just stalled a wing, I'm just above the critical AoA and my wing produces hardly any lift, so my AoA will increase further. But when I detect this early enough I might be able to get below the critical AoA by just moving the flaps forward. This is the most direct and the fastest way to change my AoA. If I mange to reduce my AoA below the critical AoA by moving the flaps forward, I produce more lift than with the flaps in the original position, so my increase in AoA is slower. If the gust, which caused my stalled wind, ends before I read the critical AoA in the new configuration this might be sufficient to regain control.



Reducing my AoA with the elevator is only my second but long term option, because I have to rotate my ship around the lateral axis and this rotation takes time.





With the flaps I can reduce the AoA for only a short period of time, but it quite often buys sufficient time to stay unstalled during the gust. If it is not sufficient, I have to use the conventional slow indirect method with the elevator.

"stalled wind, ends before I read" = "stalled wing, ends before I reach"

On 9/2/2012 3:45 AM, Chris Rollings wrote:

Most of a Very Excellent original post snipped...

...The next remark was very revealing (remember this was
only about 2 minutes after he had spun in), "I can't understand what
happened, there must have been something wrong with the elevator, I kept
pulling back on the stick but the nose wouldn't come up."

I wonder...:
1) what percentage of glider pilots think of the stick (as in elevator/pitch)
as a "nose up/down control"?
2) what percentage of glider pilots think of the stick (as in elevator/pitch)
as a "speed control"?

I believe 2) is the better/safer manner of thinking about it. It will ALWAYS
result in the correct action being taken "if the elevator quits working" at
pattern speeds. (If we've any anal aerobatic mavens, please don't muddy the
picture; this thread IS about pattern departures. :-))
- - - - - -

He had been trained, about 8 years earlier, in a regime which did include
spinning and recovery in pre-solo training, but there was no requirement
for anything like a BFR or annual check so long as he remained current. In
all probability he had not seen a spin from inside the cockpit for a number
of years. Little wonder that he did not recognise it instantly.

I'm unconvinced recurrent training is "the complete ticket". I believe that
how one fundamentally thinks (in this case, about pattern risks) is no less
crucial...perhaps even MORE crucial.

I also wonder how many glider pilots actively think when in the pattern "If I
don't get everything as I intend/need-to, I could DIE during THIS pattern!"? I
believe having such a thought in one's active awareness predisposes the mind
toward awareness that pattern departures *can* occur, and if "instant"
recognition/corrective action (reduction of AOA) does not occur, death is
likely to soon follow.

With such a thought in mind, it arguably should not matter how long ago one's
recurrent training involving pattern "departure gotcha scenarios" occurred.
- - - - - -

...Even
pilots trained under the UK system (which does include spinning and
recovery practice as part of the pre and post solo training), can't be
expected to recognise an unintentional spin that quickly if they haven't
seen and practiced one for months or years.

...The only thing that will work
is frequent practice and only instructors who are teaching spinning
regularly are really likely to get enough.

To indulge in playful quibbling...is Chris R. here suggesting that only
instructors be allowed to fly patterns, since "...only instructors who are
teaching spinning regularly are really likely to get enough (unintentional
spin entry practice to quickly recognize pattern departures)"?

OK, I know he isn't, but to quibble with his point about "practice being
necessary/crucial" to rapidly recognizing incipient pattern departures, I'm
reasonably convinced that how a person thinks, matters...a lot!!! If a person
is mentally primed for the *possibility* of incipient departure in his or her
landing pattern, then not only is s/he less likely to inadvertently play in
that corner of the sandbox, but s/he will also be mentally primed to
rapidly/correctly react with the stick.
- - - - - -

Practice is great (whether governmentally mandated or self-motivated). Just
don't fall into the mental trap of "*temporarily* (i.e. "because you're
practicing") opening your mind" to practice and its lessons, when it should
*always* be open to death-inducing possibilities.

Bob - heightened awareness pattern flyer - W.

On Sep 2, 6:45*am, Chris Rollings wrote:
Anyone any idea why the system clipped the last letter off every line in my
last post?

It didn't, all ok when I read it.

Andy (GY)

On Saturday, September 1, 2012 6:15:03 PM UTC-6, Andrew wrote:
I also have wondered how an experienced pilot can spin in from

low thermalling. It must be a full spin, with the resulting steep

recovery dive, that causes a spin-in accident: a stall doesn't lose

much height. Even the most spin-eager gliders I've flown (Dart 17

and Puchacz) always signalled an approaching stall in plenty of

time to stop an unintended spin developing. I've never

accidentally spun while thermalling at normal altitudes, not once in

my several thousand hours of gliding, so I wonder why it would be

more likely to happen low down.



One explanation might be that pilots are very stressed when

circling low, and simply don't fly as well as usual. Or maybe they

are circling unusually tightly, perhaps in a small thermal. I suspect

experienced pilots would not make these mistakes.



So I think that John Cochran's comment of August 28th may be

right. There may some unknown, unexpected risk when low-and-

slow that catches pilots out, even the best ones. Maybe small,

strong, bubbly thermals exist low down, that can perhaps

suddenly stall one wing? That would produce an immediate,

uncontrollable, violent roll, somewhat like a flick manoever,

without any advance warning signals. Not technically a spin, but

probably ending the same way: a steep dive with insufficient

height. If true, that's a risk that no amount of pilot skill can

prevent, except by adopting the sensible rules I was trained with:



1. never thermal below pattern altitude, and

2. always fly at approach speed below pattern altitude.



I have had one personal experience that supports John's

suggestion: after a normal thermal flight in the midwest, on a day

with light winds, I was on a normal final approach with wings level,

at normal approach speed (60kts). At about 100ft agl, without any

warning, my starboard wing was pushed rapidly and smoothly

upwards, and despite immediate full opposite control input, I was

put into a steep bank, I'd estimate close to 45 degrees. The surge

vanished as fast as it had arrived. After it stopped, I was able to

level the wings, correct the heading, and made a normal landing

further down the runway. It totally surprised me. I assume a

narrow thermal bubble lifted off under the starboard wing just as I

passed. I estimate the surge lasted about three seconds, so at

60kts it must have been about 300ft long. I would not have

believed it, except that it happened to me. I'm sure it would have

been much harder to cope with, if I had not been flying at

approach speed. Perhaps if I'd been flying slowly, at a higher

angle of attack, the surge might have stalled the starboard wing.

This roll event was also seen by an experienced pilot observer on

the ground, who said he was astonished to see it, and inquired

about it after I landed.



A roll upset like this has only happened to me once, so

(thankfully) its clearly a very rare occurrence, and maneageable

at approach speed. If such bubbles are baby thermals, they are

probably only in small areas, miles apart, and short lived, so

would also be rarely encountered. However a pilot who is

attempting to thermal low is presumably intentionally over an area

where baby thermals are forming, so may have a higher chance

of encountering such an effect.





May have been a dust devil, without the dust, or a thermal plume (see the Angevine article linked elsewhere in this thread), or a burst.

Over three decades ago I witnessed an SR-71 on short final get banked left to nearly 90 degrees. It was arriving from the US to an overseas location. The sky had several high based virga in the area. By the time the pilot got level, the Habu was several hundred feet left of the runway center line, over the fuel depot. After that event, Blackbirds returning from missions would do a high-speed pass down the runway to check the local air. Of course this was well before micro-burst and wind shear detectors.

The air can be fickle at any altitude, but down low it can be fatal. Which is reason 39 why I don't paraglide.

Frank Whiteley

On Saturday, September 1, 2012 10:15:02 PM UTC-6, John Sullivan wrote:
At altitude thermals flow generally vertically relatively unrestricted.

At birth, even on a perfectly flat surface, thermal air must

transition from a flat, shallow disk shaped zone feeding in from

360 degrees, crashing in, upwards ,which introduces a rotational

component. Add orographic features and wind effects to these

forces occurring in such a short period of time, over a relatively

small area, and the air is very chaotic indeed.

Although I agree that low level air can be chaotic, the disk or torus models are not accurate, though okay conceptual exercises. See the Wayne Angevine article linked earlier in this thread. If you accept that a number of plumes coalesce into larger thermal plumes, then you'll understand why you sometimes encounter a 'thermal' which for some reason you just can't seem to center in. That's because you are circling in and out of multiple adjacent plumes. Surface objects can certainly create turbulence within the wind gradient.

Frank Whiteley

Personally, I think spin training is a great thing but in Canada, although spin training including full blooded spins is standard and a checkflight with an instructor at the beginning of every season including spins is mandatory too (I've never seen a club which doesn't require it and the Soaring Association Of Canada insurance requires it as well) we really don't have that great a safety record overall. I spin my 15b at least twice a year in addition to the two spins and two incipients I have to do on the checkflight plus the spins I do with students and I actually really enjoyed doing spins in the L-13's we used to have. Does that mean I'm immune from the possibility of having a low level stall-spin? I sure hope so but I have my doubts. Having the necessity of maintaining appropriate speed in the pattern and performing well banked turns to base and final drilled into me from very early on has likely served me well though.

Hi Guys, air turbulence certainly does exist at low altitudes... I have
flown into an airfield in GB where very large aircraft are produced. The
fabrication building is HUGE and only 500m from the threshold of RW22.
With any wind speed of over 12knotts, in the right direction, this causes
ROTOR to occur on Final. (No wonder they used curved hangars in the
past.)

Just to put some maths to the speeds needed to remain above stall....

1 / cos AOB = G force eg, 1/cos60 = 2g

sqr G = increase in stall speed eg. sqr2 = 1.414

so a S+L stall speed of 40kts becomes 56.6kts at 60deg AOB. (an increase
of 16.6kts.)

Pete

At 01:09 03 September 2012, Frank Whiteley wrote:
On Saturday, September 1, 2012 10:15:02 PM UTC-6, John Sullivan wrote:
At altitude thermals flow generally vertically relatively unrestricted.
=20
At birth, even on a perfectly flat surface, thermal air must=20
=20
transition from a flat, shallow disk shaped zone feeding in from=20
=20
360 degrees, crashing in, upwards ,which introduces a rotational=20
=20
component. Add orographic features and wind effects to these=20
=20
forces occurring in such a short period of time, over a relatively=20
=20
small area, and the air is very chaotic indeed.
=20
Although I agree that low level air can be chaotic, the disk or torus
model=
s are not accurate, though okay conceptual exercises. See the Wayne
Angevi=
ne article linked earlier in this thread. If you accept that a number of
p=
lumes coalesce into larger thermal plumes, then you'll understand why you
s=
ometimes encounter a 'thermal' which for some reason you just can't seem
to=
center in. That's because you are circling in and out of multiple
adjacen=
t plumes. Surface objects can certainly create turbulence within the
wind
=
gradient.

Frank Whiteley

If I thought I was going to die every time I flew, I wouldn't fly.

The problem, as I see it, with these low altitude stall/spin accidents stems
from the desire to get home rather than landing out. Back in the '70s the
USAF called it "Get-Home-itis" and warned that it was a good way to get
killed. Pilots need to make the decision to terminate a flight before there
is no option other than landing in an unlandable place or trying to make a
low save a mile from home just to avoid the inconvenience of a retrieve.

Long ago I made the committment to never be outside of gliding distance of a
suitable landing area. I also carry the phone numbers of people who have
told me that they will come to get me if I land out. I always know where I
will land if I don't get that next thermal so there's no problem if I don't
get it and there are never any attempts to thermal at 300' AGL.

Of my conservatism causes me to rarely get more than 500Km in a day, but I
can *live* with that.


"BobW" wrote in message
...
On 9/2/2012 3:45 AM, Chris Rollings wrote:

Most of a Very Excellent original post snipped...

...The next remark was very revealing (remember this was
only about 2 minutes after he had spun in), "I can't understand what
happened, there must have been something wrong with the elevator, I kept
pulling back on the stick but the nose wouldn't come up."

I wonder...:
1) what percentage of glider pilots think of the stick (as in
elevator/pitch) as a "nose up/down control"?
2) what percentage of glider pilots think of the stick (as in
elevator/pitch) as a "speed control"?

I believe 2) is the better/safer manner of thinking about it. It will
ALWAYS result in the correct action being taken "if the elevator quits
working" at pattern speeds. (If we've any anal aerobatic mavens, please
don't muddy the picture; this thread IS about pattern departures. :-))
- - - - - -

He had been trained, about 8 years earlier, in a regime which did include
spinning and recovery in pre-solo training, but there was no requirement
for anything like a BFR or annual check so long as he remained current.
In
all probability he had not seen a spin from inside the cockpit for a
number
of years. Little wonder that he did not recognise it instantly.

I'm unconvinced recurrent training is "the complete ticket". I believe
that how one fundamentally thinks (in this case, about pattern risks) is
no less crucial...perhaps even MORE crucial.

I also wonder how many glider pilots actively think when in the pattern
"If I don't get everything as I intend/need-to, I could DIE during THIS
pattern!"? I believe having such a thought in one's active awareness
predisposes the mind toward awareness that pattern departures *can* occur,
and if "instant" recognition/corrective action (reduction of AOA) does not
occur, death is likely to soon follow.

With such a thought in mind, it arguably should not matter how long ago
one's recurrent training involving pattern "departure gotcha scenarios"
occurred.
- - - - - -

...Even
pilots trained under the UK system (which does include spinning and
recovery practice as part of the pre and post solo training), can't be
expected to recognise an unintentional spin that quickly if they haven't
seen and practiced one for months or years.

...The only thing that will work
is frequent practice and only instructors who are teaching spinning
regularly are really likely to get enough.

To indulge in playful quibbling...is Chris R. here suggesting that only
instructors be allowed to fly patterns, since "...only instructors who are
teaching spinning regularly are really likely to get enough (unintentional
spin entry practice to quickly recognize pattern departures)"?

OK, I know he isn't, but to quibble with his point about "practice being
necessary/crucial" to rapidly recognizing incipient pattern departures,
I'm reasonably convinced that how a person thinks, matters...a lot!!! If a
person is mentally primed for the *possibility* of incipient departure in
his or her landing pattern, then not only is s/he less likely to
inadvertently play in that corner of the sandbox, but s/he will also be
mentally primed to rapidly/correctly react with the stick.
- - - - - -

Practice is great (whether governmentally mandated or self-motivated).
Just don't fall into the mental trap of "*temporarily* (i.e. "because
you're practicing") opening your mind" to practice and its lessons, when
it should *always* be open to death-inducing possibilities.

Bob - heightened awareness pattern flyer - W.

Instructors are normally quite recent in spin recovery with the training glider. But the stall, spin and recovery characteristics of widely used trainers is quite different from stall, spin and recovery characteristics of the race ships we instructors use for our xc. Most of the high AoA things you can to with a K21 you can't do with one of the race-ships.

On 9/3/2012 9:43 AM, Dan Marotta wrote:
If I thought I was going to die every time I flew, I wouldn't fly.

Nor would I. I've never thought I "*was* going to die every time I flew," only
that if I didn't get certain things "right enough" on THIS approach that I
*could* die. Big difference.

There's a long history of dead pilots - better and more experienced than I -
who *did* die from not getting some basic things right.
- - - - - -


The problem, as I see it, with these low altitude stall/spin accidents stems
from the desire to get home rather than landing out. Back in the '70s the
USAF called it "Get-Home-itis" and warned that it was a good way to get
killed. Pilots need to make the decision to terminate a flight before there
is no option other than landing in an unlandable place or trying to make a low
save a mile from home just to avoid the inconvenience of a retrieve.

Good thinking...with which I'm in 100% agreement.
- - - - - -


Long ago I made the commitment to never be outside of gliding distance of a
suitable landing area. I also carry the phone numbers of people who have told
me that they will come to get me if I land out. I always know where I will
land if I don't get that next thermal so there's no problem if I don't get it
and there are never any attempts to thermal at 300' AGL.

If my conservatism causes me to rarely get more than 500Km in a day, but I can
*live* with that.

More good thinking, IMO! Most soaring pilots fly for personal satisfaction, as
distinct - say - from setting state/national/international records. Learning
how to intelligently expand one's personal limits is a key piece of the
soaring puzzle.
- - - - - -

For the record, my underlying reason to finger "misguided/absent thought
patterns" as a very real hazard within the sport of soaring comes from decades
of specifically ad-hoc discussions with the "committing PIC" regarding "flaky
patterns": e.g. "drunken sailor," low,
perplexing-to-me-under-the-circumstances, etc. Based purely on
non-quantifiable, lengthy, experience discussing these sorts of events with
the pilots involved, I think I've seen a consistent pattern of "brains not
where they need to be" in terms of not fundamentally focusing on high-priority
(to THAT pattern's ultimate outcome) items. Why that is - e.g. complacency,
distraction, pushing personal limits, whatever - is less clear to me. In any
event, how a pilot thinks, matters.

FWIW,
Bob W.