Glider Tail Stall

[jcarlyle]

Recent threads highlighted tail stalls in powered aircraft
experiencing icing. The thing that concerned me was the recovery being
exactly opposite to the wing stall that we all practice and
demonstrate, and thus have ingrained as almost automatic. It also
sounded like the thing that distinguished a tail stall from a wing
stall was buffet in the controls rather than in the airframe. This
distinction is pretty subtle to me, and in the heat of the moment I
wonder if I would apply the proper recovery.

Does anyone know, for a modern 40:1 glider, how violent a tail stall
pitch up would be?Also, if a glider has a totatally benign wing stall,
eg, non-violent wing stall break, would this imply that a tail stall
would also be non-violent?

I don't fly in icing situations, I don't have flaps, and control seal
checking is part of my preflight, so this is probably all academic.
Still, I'd like to know...

-John

[bumper]

"jcarlyle" > wrote in message
...
snip
>
> Does anyone know, for a modern 40:1 glider, how violent a tail stall
> pitch up would be?Also, if a glider has a totatally benign wing stall,
> eg, non-violent wing stall break, would this imply that a tail stall
> would also be non-violent?
snip
>
> -John

John,

Since the tail is providing down force in normal flight, if it stalls due to
icing the tail will lose downward "lift". the tail will then go up causing a
nose pitch *down*. I doubt that benign normal wing stall behavior would have
any effect on how violent a tailplane stall might be.

bumper

[[email protected]]

The aircraft pitches DOWN during a tail stall. The video link posted
earlier provides a pretty good overview.

I don't think that a benign wing stall indicates a benign tail stall.
It's about the seperation characteristics of the tail airfoil
( changed by ice ) not the wing airfoil.

Todd

[bildan]

On Feb 20, 9:00*am, jcarlyle > wrote:
> Recent threads highlighted tail stalls in powered aircraft
> experiencing icing. The thing that concerned me was the recovery being
> exactly opposite to the wing stall that we all practice and
> demonstrate, and thus have ingrained as almost automatic.

Why would the recovery be different? The tail is an inverted wing
producing a down force. You stall it by pulling back on the stick
increasing its AOA until it stalls. Releasing the back pressure
initiates a recovery - same as a wing stall.

It also
> sounded like the thing that distinguished a tail stall from a wing
> stall was buffet in the controls rather than in the airframe. This
> distinction is pretty subtle to me, and in the heat of the moment I
> wonder if I would apply the proper recovery.

It doesn't really matter. With many trainers, the buffet students are
taught to recognize as wing stall is, in fact, tail stall with a
little bit of turbulence from wing root flow separation thrown in.
Allowing the tail to stall limits up elevator authority so the wing
can never get into a full stall. Cessna 152's and SGS 2-33's are
examples.

There's a simple test for this. With the stick full back and the
glider exhibiting pre-stall buffet, apply aileron and if the glider
responds normally in roll, the wing wasn't stalled. If the wing was
stalled, the glider would probably try to spin with the application of
aileron.
>
> Does anyone know, for a modern 40:1 glider, how violent a tail stall pitch up would be?

If the tail stalls, and the CG is within limits, the glider will pitch
nose down, not nose up, and this will help effect the recovery. If
anything, modern gliders are even more benign than older designs.

Also, if a glider has a totatally benign wing stall,
> eg, non-violent wing stall break, would this imply that a tail stall would also be non-violent?

Tail stall just runs out of up elevator authority. With one
exception, tail stall is benign.

This is the exception. When the nose up moment is being produced by
something other than the elevator, the stick will be forward as the
pilot tries to limit the pitch up. In this case, the tail is
producing an up force and if the it stalls, the nose will rise further
risking a wing stall.

Two things can produce this situation. One is an aft CG and the other
is a poorly located CG hook used on a winch launch. Slab type all
moving 'stabilators' are more susceptible to this than fixed stab/
hinged elevator type tails. The fix is to be very aware of your CG
and to winch these gliders carefully.

[jcarlyle]

Bumper, Toad - thanks. Sorry for my confusion about pitch direction -
you're right, it would pitch down. The recovery with a tail stall,
though, is to pull back on the stick, not push forward. That's why I'm
worried about differentiating a tail stall from a wing stall.

Bill, please see comments embedded in your reply.

> Why would the recovery be different? The tail is an inverted wing
> producing a down force. You stall it by pulling back on the stick
> increasing its AOA until it stalls. Releasing the back pressure
> initiates a recovery - same as a wing stall.

According to the videos, if the tail stalls you need to recover by
pulling back on the stick, not pushing forward on the stick as we
usually do.

> It doesn't really matter. With many trainers, the buffet students are
> taught to recognize as wing stall is, in fact, tail stall with a
> little bit of turbulence from wing root flow separation thrown in.
> Allowing the tail to stall limits up elevator authority so the wing
> can never get into a full stall. Cessna 152's and SGS 2-33's are
> examples.
>
> There's a simple test for this. With the stick full back and the
> glider exhibiting pre-stall buffet, apply aileron and if the glider
> responds normally in roll, the wing wasn't stalled. If the wing was
> stalled, the glider would probably try to spin with the application of
> aileron.

I'll have to try this. I think I've never tried to move the ailerons
once I feel the pre-stall buffet - I just center the stick.

> If the tail stalls, and the CG is within limits, the glider will pitch
> nose down, not nose up, and this will help effect the recovery. If
> anything, modern gliders are even more benign than older designs.

Why would it help recovery? The videos say the recovery for a tail
stall is to pull the stick back.

> Tail stall just runs out of up elevator authority. With one
> exception, tail stall is benign.
>
> This is the exception. When the nose up moment is being produced by
> something other than the elevator, the stick will be forward as the
> pilot tries to limit the pitch up. In this case, the tail is
> producing an up force and if the it stalls, the nose will rise further
> risking a wing stall.
>
> Two things can produce this situation. One is an aft CG and the other
> is a poorly located CG hook used on a winch launch. Slab type all
> moving 'stabilators' are more susceptible to this than fixed stab/
> hinged elevator type tails. The fix is to be very aware of your CG
> and to winch these gliders carefully.

OK, thanks - my CG is at 60%, I have a fixed stab/hinged elevator, and
I don't winch.

-John

[Andy[_1_]]

On Feb 20, 10:15*am, jcarlyle > wrote:
>According to the videos, if the tail stalls you need to recover by
>pulling back on the stick, not pushing forward on the stick as we
>usually do.

I hate to risk adding to the obvious confususion but....

The NASA video deals with a specific case where a contamined tail
results in a uncommanded sudden downward motion of the elevator, which
in turn results in a forward stick motion, and a nose down pitch.

The situation would appear to be completely different from an
aerodynamic stall of an uncontaminated tail surface.

The use of the term "tail stall" for the icing induced pitch down
seems misleading to me since the tailplane could not be at critical
angle of attack if returning the elevator to its pre-displaced
position restores the downward tail force.

A significant difference between the two scenarios is the stick
motion associated with the event. Iced up tail - nose pitches down
as stick moves forward. Aerodynamic tail stall - nose pitches down
as stick moves aft or stay where it was.

Linking to the thread on stall awareness and recovery, the iced tail
situation that results in down elevator and uncommanded forward stick
motion may be hard to distinguish from a stick pusher event, and the
required recovery for these is exactly opposite.

Andy

[noel.wade]

On Feb 20, 9:15*am, jcarlyle > wrote:
> Bumper, Toad - thanks. Sorry for my confusion about pitch direction -
> you're right, it would pitch down. The recovery with a tail stall,
> though, is to pull back on the stick, not push forward. That's why I'm
> worried about differentiating a tail stall from a wing stall.
>
> Bill, please see comments embedded in your reply.
>
> > Why would the recovery be different? *The tail is an inverted wing
> > producing a down force. *You stall it by pulling back on the stick
> > increasing its AOA until it stalls. *Releasing the back pressure
> > initiates a recovery - same as a wing stall.
>
> According to the videos, if the tail stalls you need to recover by
> pulling back on the stick, not pushing forward on the stick as we
> usually do.
>
> > It doesn't really matter. *With many trainers, the buffet students are
> > taught to recognize as wing stall is, in fact, tail stall with a
> > little bit of turbulence from wing root flow separation thrown in.
> > Allowing the tail to stall limits up elevator authority so the wing
> > can never get into a full stall. *Cessna 152's and SGS 2-33's are
> > examples.

What? I would love to see you provide evidence to back this up. The
buffet is primarily caused by the wing stalling (i.e. causing airflow
separation) near the root of the wing, and the ugly airflow from this
striking the aft fuselage and tail as it goes by.

A tail is an upside-down wing in a conventional aircraft (canard
aircraft are the exception) - therefore raising the angle of attack of
the wing *decreases* the angle of attack of the tail.

NOTE: There is a difference between a tail stall and an aircraft who's
tail is sized and limited in elevator travel to prevent the pilot from
really getting a good full stall with a break. My DG-300 is an
example of this - I can get a stall break if I perform an accelerated
stall; but if I start in slow flight and gradually increase the stick
pressure, the aircraft doesn't exhibit a true "stall break" - it just
buffets a lot and develops a good rate of descent.

> > There's a simple test for this. *With the stick full back and the
> > glider exhibiting pre-stall buffet, apply aileron and if the glider
> > responds normally in roll, the wing wasn't stalled. *If the wing was
> > stalled, the glider would probably try to spin with the application of
> > aileron.

Uhhh, no not necessarily. You are ignoring the effects of wing taper,
twist, and span-wise distribution of lift. Wings can (and ARE)
designed to stall near the wing root first, and then progress outward
along the span. So you can get "stall buffet" and still have aileron
control because the outboard parts ofthe wings are not stalled (they
are flying at a lower effective angle of attack and therefore still
have clean airflow over part or all of the wing chord). It has
nothing to do with the tail stalling!

Oh, and before you do that test, please remember that applying aileron
input will make one of the ailerons move _down_ - thus increasing the
angle of attack on that part of the wing. If you've got a partially-
stalled wing and you increase the angle of attack on the outboard
(unstalled) part of it, you may stall the whole wing. Meanwhile, you
are _decreasing_ the angle of attack on the wing that has the aileron
deployed upwards. Thus that wing will likely _not_ completely stall.
Everyone knows what happens when one wing stalls and the other doesn't
completely stall, right? Spin time! This is why we teach people not
to use much (or any) aileron input when feeling the pre-stall buffet.
Again, this has nothing to do with the tail stalling.

--Noel

[[email protected][_2_]]

To add to the confusion:

Many modern gliders are elevator limited - full aft stick just won't
result in enough AOA to stall the wing. Nothing to do with the tail
being stalled. In fact, it's "lifting" just fine, just in the "down"
direction (which could be up if you are at the top of a loop). If the
tail did actually stall, you would get a brisk nose down pitch rate, I
would think! It would be almost the same as the horizontal tail
falling off. Think about it....

Also, the tail on modern gliders do not always push "down". Depends
on speed, AOA, G-load, CG location, flap position, etc. You have to
look at the entire lifting contributions of all the parts of the
glider. Stability is due more to decalage. Look it up.

It's amazing how little most pilots know about how their aircraft
really work....including yours truly!

Kirk
66

[jcarlyle]

Andy,

Let me reduce my original question to a specific situation. Suppose
you're flying in 60 degree weather, so no surface is contaminated with
ice. Suddenly, the nose pitches down and the stick stays where it
was.

My question is: how do you know if you've suffered a wing stall (where
the recovery is to push the stick forward), or a tail stall (where the
recovery is to pull the stick back).

-John

On Feb 20, 1:13 pm, Andy > wrote:
> I hate to risk adding to the obvious confususion but....
>
> The NASA video deals with a specific case where a contamined tail
> results in a uncommanded sudden downward motion of the elevator, which
> in turn results in a forward stick motion, and a nose down pitch.
>
> The situation would appear to be completely different from an
> aerodynamic stall of an uncontaminated tail surface.
>
> The use of the term "tail stall" for the icing induced pitch down
> seems misleading to me since the tailplane could not be at critical
> angle of attack if returning the elevator to its pre-displaced
> position restores the downward tail force.
>
> A significant difference between the two scenarios is the stick
> motion associated with the event. Iced up tail - nose pitches down
> as stick moves forward. Aerodynamic tail stall - nose pitches down
> as stick moves aft or stay where it was.
>
> Linking to the thread on stall awareness and recovery, the iced tail
> situation that results in down elevator and uncommanded forward stick
> motion may be hard to distinguish from a stick pusher event, and the
> required recovery for these is exactly opposite.
>
> Andy

[[email protected][_2_]]

Just remembered that there is a good discussion about glider-induced
towplane tailstalls - both horizontal and vertical - in the BGA
towplane manual. The rudder one kinda sounds like fun, actually, as
long as I had a parachute and lots of altitude!

Sorry, no link, I'll try to find it and post later.

kirk
66

[bildan]

On Feb 20, 10:15*am, jcarlyle > wrote:
> Bumper, Toad - thanks. Sorry for my confusion about pitch direction -
> you're right, it would pitch down. The recovery with a tail stall,
> though, is to pull back on the stick, not push forward. That's why I'm
> worried about differentiating a tail stall from a wing stall.
>
> Bill, please see comments embedded in your reply.
>
I think the others made the essential point that the video subject was
a special situation where ice on the tail leading edge led to a
separation bubble on the lower surface with flow re-attaching aft of
the hinge line. The re-attached flow was sucking the elevator down
(nose down) so the pilots were advised to pull back to counter this
force to retain control of their aircraft.

The violent pitch down was due to this effect. The video also talked
about non-linear elevator effects which could lead to PIO's

As for the tail/wing stall discussion, unless you've flown a glider
with yarn tufts on the wing and tail, this is hard to visualize.

Yes, of course, the wing is designed to stall at the root first. In
fact, unless there is a very effective root fillet, there will be some
root flow separation visible at any AOA.

In every case I know of, the yarn tufts show full flow separation on
both upper and lower surfaces of the tail when as nose 'breaks'
suggesting a wing 'stall' to the pilot. At the same time the wing
tufts show attached flow over the majority of the wing which is why
the ailerons work as expected. You can say the tail just loses
effectiveness or you can call it a tail stall - the distinction isn't
really important.

[Andy[_1_]]

On Feb 20, 12:48*pm, jcarlyle > wrote:
> Let me reduce my original question to a specific situation. Suppose
> you're flying in 60 degree weather, so no surface is contaminated with
> ice. Suddenly, the nose pitches down and the stick stays where it
> was.

I don't know how to answer that without knowing more about the flight
condition and the stall margin. If the sudden pitch down was
associated with a loud noise I'd bail out!

Andy

[[email protected]]

On Feb 20, 2:48*pm, jcarlyle > wrote:
> Andy,
>
> Let me reduce my original question to a specific situation. Suppose
> you're flying in 60 degree weather, so no surface is contaminated with
> ice. Suddenly, the nose pitches down and the stick stays where it
> was.
>
> My question is: how do you know if you've suffered a wing stall (where
> the recovery is to push the stick forward), or a tail stall (where the
> recovery is to pull the stick back).
>
> -John

I don't know how you would encounter a tail stall in a glider without
ice buildup or some severe damage to the tail. It's just not a
realistic scenario. In other words, don't worry about it.

Todd
3S

[noel.wade]

On Feb 20, 12:11*pm, Andy > wrote:

> > Let me reduce my original question to a specific situation. Suppose
> > you're flying in 60 degree weather, so no surface is contaminated with
> > ice. Suddenly, the nose pitches down and the stick stays where it
> > was.

If you are flying within the CG limits and at a reasonable speed (i.e.
within the envelope), then the main wing will stall before the tail.
Any modern aircraft will be designed to have good stability when
loaded within the CG limits and flown at reasonable speeds.

A propensity for the tail to stall in these conditions would be
similar to what would happen when an aircraft is loaded aft of the CG
limits and stalls (look up "deep stall"; and once you understand it
you will never load an aircraft aft of the recommended CG limit
_ever_). I've seen this happen with experimental R/C aircraft that I
was testing (as a hobbyist, not as a professional).

Of course, flying outside of the CG limits and/or pulling high-G
aerobatics (wherein you might induce sudden and extreme AOA changes in
the flying surfaces) are another situation entirely...

The beauty is if you're not fying an aircraft with contaminated flying
surfaces, both a tail tall and a main wing stall should have roughly
the same recovery procedure: Allow the aircraft to regain flying
speed and reduce the angle-of-attack (once air is flowing normally
over the aircraft, you're fine), and then return to a normal pitch-and-
bank attitude. The only difference is in recognizing what you need to
do in order to regain flying speed. If you're holding the stick back
and the airspeed needle is down around zero, stop holding the stick
back! If you're holding the stick forward and the ASI is resting on
its stop, relax the forward pressure!

The vast majority of the time, bringing the controls closer to neutral
is the right thing to do - mostly because of the built-in stability of
nearly all aircraft produced in the last 60 years. But again, this is
true only when the aircraft is loaded within the CG limits.

Kirk - I really lament the fact that so few pilots truly understand
what the air is doing as it flows over their aircraft. Seeing the
diagram in a pilot handbook and memorizing answers for the FAA test is
just not good enough. SO MANY "pilot-error" accidents could be
avoided, if only people had a better grasp of the cause-and-effect
relationship between the cockpit controls, the flying surfaces (as the
controls are moved), and the airflow over the aircraft. Being able to
understand "if I do X, then Y will happen" (in terms of the airflow
and the aerodynamics) goes a long way towards knowing how to get out
of trouble, or avoid it altogether! Without this understanding, I
think a lot of pilots don't really know what risks they're taking as
they blithely fly along, and they don't understand how their safety-
margin is changing as they take different actions in the cockpit.

*sigh* OK, rant over... :-P

--Noel

[Jim White[_2_]]

At 20:47 20 February 2009, wrote:
>
>I don't know how you would encounter a tail stall in a glider without
>ice buildup or some severe damage to the tail. It's just not a
>realistic scenario. In other words, don't worry about it.
>
>Todd
>3S

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

[bildan]

On Feb 21, 2:15*am, Jim White >
> 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

Define "necessary".

If you find minimal competence acceptable, chancing that you will
never encounter a situation beyond your skill, you might get away with
an ignorance of aerodynamics.

But, if you want to achieve anything beyond that, If you want to
significantly enhance your safety, yes, it is necessary.

[jcarlyle]

Jim,

Thanks for sharing your story. What I'm most gratified to learn is
that normal recovery techniques worked.

-John

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.

[[email protected]]

On Feb 21, 4:15*am, Jim White > wrote:
> At 20:47 20 February 2009, wrote:
>
>
>
> >I don't know how you would encounter a tail stall in a glider without
> >ice buildup or some severe damage to the tail. *It's just not a
> >realistic scenario. * *In other words, don't worry about it.
>
> >Todd
> >3S
>
> 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

Jim,

Was the gust vertical ? and in a downward direction ? That's what I
would think was necessary to produce a tail stall. A downward gust
would exceed the stall angle of attack on the tail and produce a nose
down pitch.

Of course a strong gust can produce pitch excursions without causing
tail stall specifically.


On knowing how gliders really work, I think that some knowledge of
aerodynamics is mandatory to be a safe pilot, but some is optional.

For example:

Mandatory knowledge:
HOW lift relates to angle of attack (especially stall).

Optional knowledge:
WHY airfoils work the way they do.

Mandatory knowledge allows a pilot to correctly fly the aircraft.
Optional might help support that, but isn't critical to the flight.
Being an aerospace engineer, I hear pilots explain a lot of flight
physics completely wrong, but they are competent and safe pilots.
Conversely, I hear some pilots explain the physics correctly, but
would not allow a loved one to fly with them.

IMHO all the aerodynamics that I pilot needs to understand is in
"Stick and Rudder" by Wolfgang Langwiesche.

Todd
3S

[Jim White[_2_]]

At 15:49 21 February 2009, bildan wrote:
>On Feb 21, 2:15=A0am, Jim White
>> 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
>
>Define "necessary".
>
>If you find minimal competence acceptable, chancing that you will
>never encounter a situation beyond your skill, you might get away with
>an ignorance of aerodynamics.
>
>But, if you want to achieve anything beyond that, If you want to
>significantly enhance your safety, yes, it is necessary.
>

I know my glider's VNE, Va, and stall speed.
I know its G limits, CofG limits, flap speed limits.
I know that it is cleared for loops and spins but not inverted flight.
I know that stall speed will increase by 1.5 at 60degrees of bank.
I know that contamination (rain, ice, or bugs) on the leading edge spoils
the magic and increases stall speed by an undefined amount.
Oh, by the way, I have been taught about high speed stalls.

What other aerodynamics stuff do I really need to know?

If I stay within the flight envelope and concentrate on my flying,
lookout, and xc tactics I reckon I should be safe without actually knowing
how it actually works.

It is a bit like met. I can't do the maths but I can read a tephi.

Jim

[Surfer!]

In message
>,
bildan > writes
<snip>
> If you want to
>significantly enhance your safety, yes, it is necessary.

It is? If something goes wrong I'll be too busy trying to aviate my way
to safety to think about the aerodynamics. Hopefully they have informed
the training I have received (which is what I successfully used to
resolve in the only significant incident I've been in so far) , but the
training is devised by much better and more experienced pilots than
myself.

--
Surfer!
Email to: ramwater at uk2 dot net

[noel.wade]

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

[[email protected]]

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

[Ian Cant]

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

[[email protected]]

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

[JC]

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

[[email protected]]

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.

[noel.wade]

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

[Jim White[_2_]]

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

[Andy[_1_]]

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

[Eric Greenwell]

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
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

[noel.wade]

Glad to see people Dog-piling on me and exagerating my comments...
*smirk* Makes me wonder why are you folks feeling so threatened and
defensive. I'm not advocating a college course in order to get your
pilot's license, I'm not calling for any changes at all in my
comments... Why are folks blowing this out of proportion?

Please re-read my original post carefully. I never said you had to
have a "perfect" understanding of aerodynamics. I also never said it
would make you a fast race pilot. I'm saying that pilots should
understand what is happening - aerodynamically speaking - when they
deflect the control surfaces on their aircraft.

The sum total of your knowledge should not be "I push the stick to the
right to make the airplane roll right". It should be "I push the
stick to the right which makes the left wing aileron go down,
increasing angle of attack and therefore the lift on that part of the
wing. Simultaneously, the right wing aileron is doing the opposite
movement with the opposite effect. The net _effect_ is that the
aircraft rolls toward the right - with a bit of adverse yaw because
the increased lift on the left wing has a bit of rearward action/angle
on it."

And since people are taking me so literally, let me clarify that I'm
not advocating you talk through this whole sequence with each control
movement - but it _should_ be something you intuitively know is
happening. In a cause-and-effect system like flying, you need to
understand the "cause" bit - because the "effect" is only guaranteed
under certain limited conditions.

What I am claiming, is that knowing this stuff will make you a better
pilot and perhaps a more consistent pilot. Most of all it will make
you a safer pilot. As Bob Wander is fond of saying, "your aircraft is
your life support system". I think its mind-boggling that people are
willing to use a life-support system they don't understand.

Regarding the sarcastic "National Team" comments: I'm working on
that. :-) I've only been flying for 2 years (well, 2.5 if you count
powered aircraft as "flying"). I will be competing in my first
Regionals here in late April at Warner Springs. Last summer I bought
a DG-300 and took my first 7 flights out of an unfamiliar airport
(Ephrata). I made 3 flights in excess of 400km (at 82 - 97km/hr); and
all 7 flights were in excess of 200km - even the first couple of
familiarization flights and on days with OD and rain.

I'll let this die now - I'm sure many of you will post follow-on
comments that will tempt me to jump back in and clarify - but I'll try
to resist. If you're dead set on arguing this, nothing I say will
change your mind - so I'll try not to waste everyone's time.

--Noel

[[email protected]]

On Feb 24, 3:36 pm, "noel.wade" > wrote:
> Glad to see people Dog-piling on me and exagerating my comments...
> *smirk* Makes me wonder why are you folks feeling so threatened and
> defensive. I'm not advocating a college course in order to get your
> pilot's license, I'm not calling for any changes at all in my
> comments... Why are folks blowing this out of proportion?
....

> --Noel

Noel,

Maybe are responding to the tone of this post by you:

> 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)!!

After they had stated reasonable positions on how much aerodynamic
knowledge is needed during flight. So don't be suprised that people
kick back.

Todd Smith
3S

[Fred Blair]

It is impossible to separate the aerodynamics that you learn from the books
from the total learning experience putting things you learned in the book
together with things you learned from your Instructor. The total package is
what makes us better pilots. I know that if you get into a spin because of
a bad turn from base to final, you are not going to have time to decide,
'did my tail stall' or what. I think this topic got started when the video
came out about the videos about icing causing a tail to abruptly go down
when the area of stagnant air moved back to the rear of the stabilizer.
This caused a movement that is not expected and the response has to be a
learned not an instinctive one from regular 'stall' warning signs. You have
to have the whole package of book facts and mechanical skills learned in the
cockpit to make a safe pilot.
"Eric Greenwell" > wrote in message
...
> 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
> * Change "netto" to "net" to email me directly
>
> * Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
> * New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more
>
> * "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

[Jim White[_2_]]

Many thanks to those that supported my argument. My reaction was indeed
against the SHOUTED proposition that I was a dangerous numb head because I
felt that a knowledge of aerodynamics was not fundamental to my flight
safety.

Noel, seems I have an edge on you. I have been flying 15 years and have
flown in 7 UK Nationals competitions, sometimes doing quite well. I
suspect that when you have built up some experience you may temper your
assertions.

Jim

[noel.wade]

Argh, so much for my resisting a follow-up:

1) I need to apologize. My flight experience may be small, but my
computer experience stretches back to age 6, long before there was an
"internet". In the good old days of dial-up modems (300 baud, baby)
it was common to use ALL CAPS as a replacement for bold text, and
_underscores_ to indicate italics. The "CAPS is SHOUTING" standard
evolved later (sometime in the late 80's if I recall correctly). I
understand it, and hate shouting as much as everyone. But I still
sometimes slip back into all caps when I'm trying to really stress
certain words or make things stand out. My intent was not to yell
_at_ people, but rather to raise my voice in disbelief that people
don't see (or care about) the connection between their understanding
of how air flows over their aircraft and how it affects their safety.
The whole "lack of vocal inflection in typed communications" thing
still rears up and bites us all from time to time.

2) One last time (and I promise, it really is the last time in this
thread I'll post): I think people took my initial comments too far.
My main point is that I see too many pilots talking (and worse, too
many instructors teaching students) about moving the controls and how
the aircraft reacts. And the connection to aerodynamics is lost.
Sure, people read in a textbook about lift, drag, and gravity. And
they see a pretty picture about angle of attack. But then once they
take the FAA written test, the knowledge falls out of their brain and
they never think about it again. The thing is (and this is my central
point) - the aircraft doesn't _care_ what you do with the controls or
what the textbook says. The aircraft is going to react to what the
air around it is doing; and the controls are just a means to
manipulate that airflow (and only to a limited extent). However good
or however safe a pilot may be, I personally believe they could be
even _better_ if they keep that rattling around in the back of their
brain. Not thinking through every step or any calculations; but just
the general ideas and concepts and an understanding of how it all
works. And I believe a pilot who doesn't have this knowledge and
doesn't think about this stuff is at a much greater risk of reacting
improperly in an emergency situation (or unintentionally doing
something that increases their risk-factor during a flight).

Alright, I promise I'll really let the thread die now... :-P

--Noel
P.S. Jim - just a note about experience: I flew R/C gliders for a
few years before going "full-scale". My favorite thing was to fly 24"
wingspan flying wings on small hills (20 - 30 feet tall) using ridge/
slope lift. The total CG envelope was 1/8th of an inch in size, and
total movement of the control surface was about 3 millimeters (full
back-stick to full forward-stick). And we flew 1 - 2 feet off the
deck a lot of the time... Its different from flying full-scale stuff,
but it really trains the hands and makes the pilot focus! ;-)