Glider Tail Stall

I had a long post I started to write on this topic, but I can shorten
it down to two things:

1) No one is saying you have to be able to do aerodynamic calculations
or design an airplane, just that you understand aerodyanmics in
general and the cause-and-effect nature of your control inputs and how
the glider is going to react to different situations (angle of attack,
horizontal and vertical gusts, etc).

2) I continue to be astounded by the pilots out there who are
perfectly happy to GAMBLE THEIR LIVES by taking part in an activity
where they don't know what it is they're doing; AND they will even
state outright that they don't CARE that they don't know (like some of
the people who said so in this thread)!!

Do they really put so little value their well-being? Or do they just
think that an accident will never possibly happen to them, no matter
how poorly (_or_ how well) they fly?

Bottom line: If you don't know WHAT you're doing to the aircraft and
the air, then you have no way to judge risk or know how safe you're
being with your flying. So you _are_ GAMBLING - its not a "measured"
risk, and you aren't able to manage your level of risk if you don't
know what it is! And the penalty for failure is injury or death...
Seems like education and understanding are a small price to pay!

When you are in a stall or a spin or having an emergency, the glider
won't care if you were "taught a certain way" by more experienced
pilots. The aircraft also doesn't care what the textbook says. And
the atmosphere is _going_ to behave in ways that don't go along with
the textbook examples. All the glider cares about is proper airflow
and aerodynamic principles - and if you don't know those things then
you aren't guaranteed to be able to recover from the problem.

Good luck with that...

--Noel

On Feb 22, 12:57*am, "noel.wade" wrote:
I had a long post I started to write on this topic, but I can shorten
it down to two things:

1) No one is saying you have to be able to do aerodynamic calculations
or design an airplane, just that you understand aerodyanmics in
general and the cause-and-effect nature of your control inputs and how
the glider is going to react to different situations (angle of attack,
horizontal and vertical gusts, etc).

2) I continue to be astounded by the pilots out there who are
perfectly happy to GAMBLE THEIR LIVES by taking part in an activity
where they don't know what it is they're doing; AND they will even
state outright that they don't CARE that they don't know (like some of
the people who said so in this thread)!!

Do they really put so little value their well-being? *Or do they just
think that an accident will never possibly happen to them, no matter
how poorly (_or_ how well) they fly?

Bottom line: *If you don't know WHAT you're doing to the aircraft and
the air, then you have no way to judge risk or know how safe you're
being with your flying. *So you _are_ GAMBLING - its not a "measured"
risk, and you aren't able to manage your level of risk if you don't
know what it is! *And the penalty for failure is injury or death...
Seems like education and understanding are a small price to pay!

When you are in a stall or a spin or having an emergency, the glider
won't care if you were "taught a certain way" by more experienced
pilots. *The aircraft also doesn't care what the textbook says. *And
the atmosphere is _going_ to behave in ways that don't go along with
the textbook examples. *All the glider cares about is proper airflow
and aerodynamic principles - and if you don't know those things then
you aren't guaranteed to be able to recover from the problem.

Good luck with that...

--Noel

I'd say that in any of these situations, knowledge of aerodynamic
principles will not be of much use. Because you will not have the
time to work out a course of action from those principles DURING the
flight. The time to work out the course of action is ON THE GROUND,
BEFORE THE FLIGHT.

Todd
3S

At 13:06 23 February 2009, wrote:
I'd say that in any of these situations, knowledge of aerodynamic
principles will not be of much use. Because you will not have the
time to work out a course of action from those principles DURING the
flight. The time to work out the course of action is ON THE GROUND,
BEFORE THE FLIGHT.

..and presumably based on some knowledge of aerodynamic principles ?

Ian

On Feb 23, 9:45*am, Ian Cant
wrote:
At 13:06 23 February 2009, wrote:

I'd say that in any of these situations, knowledge of aerodynamic
principles will not be of much use. *Because you will not have the
time to work out a course of action from those principles DURING the
flight. *The time to work out the course of action is ON THE GROUND,
BEFORE THE FLIGHT.

.and presumably based on some knowledge of aerodynamic principles ?

Ian

Of course.

But the beautiful thing about learning on the ground, is that you can
draw on the knowledge of others to work out the plan of action during
flight.

Todd
3S

At my club we had some tail stall situations with a Cirrus Standard
during winch launches.
With some of the lighter pilots the glider would tend to overrotate on
takeoff and when the stick was pushed forward to lower the nose it
only got worse.
Since it´s an all flying stab, pushing forward would increase the
already large angle of attack and stall the tail. A fast thinking
pilot found that a quick pull on the stick would unstall it. Sometimes
it required ´´pumping´´ a couple of times to regain full pitch
control.
After a few unpleasant launches we did a weight and balance and found
that the glider was tail heavy. After correcting this condition the
overrotation tendency was greatly reduced but it´s still possible.
I guess that´s one of the reasons they don´t make gliders with all
flying stabs anymore.

Regards,

Juan Carlos

On Feb 21, 4:15*am, Jim White wrote:
I am pretty sure I have encountered a tail stall due to a gust experienced
in straight and level flight in a K18 at 50kts. I was alarmed to find
myself suddenly pointing at the ground! Normal recovery worked. Thankfully
has never happened again.

I know how gliders work...magic. Is it really necessary to know how stuff
works to fly a glider? Design and build one yes, but to fly one?
Jim

before reading this thread I did not know anything about tail stall,
I did not even know that such thing existed nor I new that horizontal
tail push down not up......
but I think I did experience one tail stall on a K21:
I was flying from the front seat with a young passenger holding the
stick
for the first time in his life to keep the glider flying straight at
50kts, while I was monitoring the front stick to
dumpen sudden movements if any, the K21 from level flight pitched the
nose down at least 30/40 degrees.
It was fun, as usual, and recovery was normal.
It is interesting to note the K21 from level flight, full stick back
will not stall,
but only sinks more with mush controls,
to make the K21 stall and have the nose pitch down we normally climb
at about 30 degrees.

maybe it was a tail stall due to a gust............
too bad I did not have a vid cam at that time!!!
because after the flight when I asked for explanations, I did not get
any.
.......... they were staring at me, looking funny.

On Feb 23, 5:06 am, wrote:
I'd say that in any of these situations, knowledge of aerodynamic
principles will not be of much use. Because you will not have the
time to work out a course of action from those principles DURING the
flight. The time to work out the course of action is ON THE GROUND,
BEFORE THE FLIGHT.

Todd


A general course of action is good to work out ahead of time, yes.

HOWEVER, if you look at some of the famous accidents and close-calls
in aviation history, you'll find that the people who _intuitively_
understood what was going on and were able to correct for their unique
situation are the ones that made it out OK. There are plenty of
"pilot error" accidents where people took action based on reflex, and
it made the situation worse (instead of better) and killed them.
Emergencies aren't always straightforward and they don't work out like
the textbook. If you find yourself in an unusual situation you have
to be able to detect what's different or unique, and modify your pre-
planned course of action to suit the situation.

That's why I think learning stall and spin correction "by wrote", for
example, is very bad. Instead of teaching people to "push the stick",
its better to teach them how to un-stall the wing by reducing the
angle of attack. Now, in _most_ cases, that means reducing back-
pressure or a forward stick input - but not in _all_ cases. If you
simply have a Pavlovian response to situations and don't understand
the situation or what your reaction is doing, sooner or later you're
going to get it wrong and make a situation worse instead of better
(for instance: in a spiral dive if you react like you're in a spin).

Now, some of you may be thinking "geez, this guy is talking about
these long chains of reasoning that you must go through to diagnose
the situation and then figure out the appropriate response - there's
no WAY you can do that while flying!" To those people I say this:
You don't think that catching a ball is too hard, do you? But your
brain is doing some serious math to calculate the trajectory of the
ball so that your hands are in the right position to catch it. And
even people with modest IQs can catch a ball quite well (as a side
note: I make no claims about my IQ _or_ my ability to catch!)...

The difference is that you've been catching objects with your hands
since you were very young, so its all very normal and intuitive.
Flying is something that most of us don't do on a daily basis through
our formative years. In flying, you just haven't spent enough time
practicing and working on understanding the knowledge so that it
becomes a fast or intuitive process. You probably felt similarly
overwhelmed when you first learned to fly and were trying to handle
the aircraft controls while visually scanning all around the aircraft
at the same time - especially if you then had to add juggling radio
calls on top of it! But with practice and understanding, it became
easier and was no longer overwhelming. The same thing is true when it
comes to thinking about the aerodynamics of your flight, as you fly.

Take care,

--Noel

At 00:26 24 February 2009, noel.wade wrote:
HOWEVER, if you look at some of the famous accidents and close-calls
in aviation history

Please tell us about these famous accidents and how a knowledge of
aerodynamics would have averted them.

(for instance: in a spiral dive if you react like you're in a spin).

Geez Noel. Are you saying I don't know the difference between a spiral
dive and a spin? That was learned very early in my gliding career. Or
maybe you are saying that because I don't understand how a wing works I
won't consider whether I am in a spin or spiral dive and so apply the
wrong control inputs? Does anyone else see the connection? I don't.

There is always plenty to do in my cockpit other than thinking about
aircraft design. My glider simply does what it was designed to do and in
the way the manual tells me it does.

Jim

On Feb 24, 1:00*am, Jim White wrote:
Does anyone else see the connection? I don't.

I don't claim any expertise in aerodymanics but I have never felt that
it placed any limitation on my ability as a pilot. With a perfect
knowledge of aerodynamics and a full understanding of the
characteristics of the glider being flown, all pilots still lack
complete knowledge of the airmass they are flying in. How can the
aero solution be derived without a knowledge of the airmass behavior?

I very much doubt there is a good correlation between pilot
proficiency, particularly cross country flying skills, and the
theoretical knowledge of aerodynamics. If I'm wrong we should see
Noel in the National team quite soon.

Andy

Andy wrote:
On Feb 24, 1:00 am, Jim White wrote:
Does anyone else see the connection? I don't.

I don't claim any expertise in aerodymanics but I have never felt that
it placed any limitation on my ability as a pilot. With a perfect
knowledge of aerodynamics and a full understanding of the
characteristics of the glider being flown, all pilots still lack
complete knowledge of the airmass they are flying in. How can the
aero solution be derived without a knowledge of the airmass behavior?

I very much doubt there is a good correlation between pilot
proficiency, particularly cross country flying skills, and the
theoretical knowledge of aerodynamics. If I'm wrong we should see
Noel in the National team quite soon.

I have to agree with Andy. I've flown gliders for 33 years, 6000 hours
(5500 cross-country hours), and instructed for about 12 years. I am
geeky to the point of annoyance about aerodynamics (I'm sure pilots
around the world hesitate over the "send" button because they are afraid
I will whip out my "Fundamentals of Sailplane Design" and ruin a good
argument). And yet, I can't really think of how my knowledge of
aerodynamics has kept me safe all these years.

Same for my students. Sure, we talked about aerodynamics, but it was to
reinforce the lesson or to satisfy curiosity, not to equip them to deal
with a flight problem (literally) "on-the-fly".

And frankly, most of us have such a simplistic understanding of
aerodynamics, it's probably best we don't try to use it to deal with a
flight situation. Shoot, we still have discussions about which way the
elevator is 'lifting', yet pilots aren't crashing because they don't
know the right answer.

I'd like to hear of examples where a knowledge of aerodynamics saved the
day. I don't have any I can recall, but maybe someone's comments will
jog my memory.

--
Eric Greenwell - Washington State, USA
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