Newbie seeking advice [Archive]

Bill Daniels

June 11th 04, 03:55 PM

Doug Hoffman

June 11th 04, 04:09 PM

.. wrote:

> I went for a ride in a glider many years ago and was immediately taken with
> the whole experience. I have always wanted to fly and now have the time to
> do it as I am finished with my skydiving career. Before I sell my rigs I
> wanted to ask a question. Do any of you wear pilot rigs? Before I trade
> some gear for a pilot rig....what is the reality of actually getting out of
> a glider if you have a structural failure or something catastrophic? I am a
> realist and can accept the fact there are inherent risks up there believe
> me, but I don't want to buy a rig if it's a mute point. Do any of you wear
> rigs? Thanks for the advice.

I don't have the statistics, but there are many cases where the pilot's life
has been saved by using the chute. There are also many cases where the
chute, as you suggest, may not help you; such as a low altitude spin,
incapacitating mid-air, etc. As has already been mentioned, wearing a
chute is common and required in SSA sanctioned and other contests.

Regards,

-Doug

stephanevdv

June 11th 04, 05:09 PM

Research by the German Akafliegs (academic flying clubs) indicates that
one is unlikely to be able to bail out safely with less than 700 m
altitude. The chute needs only 100 m to deploy, but it is indeed the
egress, under stress and often under higher G forces, that takes time.
They also think it unlikely for anybody to be able to jump under more
than 1.5 positive G. That makes the NOAH system a very good idea.
Unfortunately, we often prefer to invest in performance or electronics
rather than safety devices... (in Germany, NOAH costs approximately 2
500 EUR, + 800 EUR installation, + VAT).

But every year, glider pilots are saved by their chutes - some bailed
out at lower altitudes than indicated above. I don't have a glider, but
I bought a parachute early on, just to be sure it's regularly repacked
and properly treated (not like some club parachutes I know of). If you
fly regularly, it's a good investment! If carefully chosen, it's also
an element of comfort.

--
stephanevdv
------------------------------------------------------------------------
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- A website for Australian Pilots regardless of when, why, or what they fly -

Ulrich Neumann

June 11th 04, 09:04 PM

"." > wrote in message >...
> I went for a ride in a glider many years ago and was immediately taken with
> the whole experience. I have always wanted to fly and now have the time to
> do it as I am finished with my skydiving career. Before I sell my rigs I
> wanted to ask a question. Do any of you wear pilot rigs? Before I trade
> some gear for a pilot rig....what is the reality of actually getting out of
> a glider if you have a structural failure or something catastrophic? I am a
> realist and can accept the fact there are inherent risks up there believe
> me, but I don't want to buy a rig if it's a mute point. Do any of you wear
> rigs? Thanks for the advice.

Welcome to Soaring!

No matter what you intend to fly in, get yourself a chute! These are
typically round, 26' dia. canopies, built for extremely rapid, manual
deployment. There are also rectangular rescue chutes available, but
according to the master rigger who repacks my chute, the average guy
could get into trouble with them since they require skill and
knowledge to handle them. Get something that is called 'Chair-chute'
or 'Thin-Pack'. Keep in mind that - as Bill put it - we intend to
bring the glider back and therefore we typically lie or sit on the
chute for a couple of hours. If you are qualified to repack your own
rig, change your mind-set, too: think "Comfort"! There is nothing more
annoying than getting the chute back repacked only to discover that
there is a lump pushing into your back.
Check out brand names like National, Softie or Strong, they have what
you are looking for.

Uli Neumann
Libelle 'GM'

Dan D

June 12th 04, 04:49 PM

seems to me that a chute large enough to carry the pilot and glider would be
the best bet.
forget the bailout. if for whatever reason you fly yourself into a situation
or midair and crash is inevitable, deploy, save yourself as well as the
glider.

"." > wrote in message
om...
> I went for a ride in a glider many years ago and was immediately taken
with
> the whole experience. I have always wanted to fly and now have the time
to
> do it as I am finished with my skydiving career. Before I sell my rigs I
> wanted to ask a question. Do any of you wear pilot rigs? Before I trade
> some gear for a pilot rig....what is the reality of actually getting out
of
> a glider if you have a structural failure or something catastrophic? I am
a
> realist and can accept the fact there are inherent risks up there believe
> me, but I don't want to buy a rig if it's a mute point. Do any of you
wear
> rigs? Thanks for the advice.
>
>

Gldcomp

June 12th 04, 07:52 PM

"." > wrote in message
om...
> I went for a ride in a glider many years ago and was immediately taken
with
> the whole experience. I have always wanted to fly and now have the time
to
> do it as I am finished with my skydiving career. Before I sell my rigs I
> wanted to ask a question. Do any of you wear pilot rigs? Before I trade
> some gear for a pilot rig....what is the reality of actually getting out
of
> a glider if you have a structural failure or something catastrophic? I am
a
> realist and can accept the fact there are inherent risks up there believe
> me, but I don't want to buy a rig if it's a mute point. Do any of you
wear
> rigs? Thanks for the advice.

Forget all the "I think this", "I think that" very common to
rec.aviation.soaring.
There are all kinds of PHDs in every science here, but unfortunately very
little flying.
Few experienced pilots write here, that's why so many people say things like
"sit on the parachute for a couple of hours".
Competition and cross-country flights in gliders very rarely are less than 6
hours in duration.
Unfortunately, 70% of all glider pilots don't really know what that is,
hence the "couple hour fliers" in rec.aviation.soaring.
Same thing applies for those who "think" there are more bail-outs because of
collision than structural failure...
OF COURSE the rare bail-outs are motivated by collision.
Gliders don't fall appart in flight by themselves like ultralights and other
crazy flying machines.
Gliders are, after all, certified aircraft.

So here is the gist :
Glider pilots almos all over the world are required to wear parachutes
because of the risk of collision with other gliders while thermalling.
That is the only reason we are "required" to wear parachutes.
In the USA parachutes are not "required" except in competition and aerobatic
flight, so, the USA is the exception.

Sure a parachute might also save you in case of structural failure, but the
vast majority of bail-outs were motivated by mid-air collisions.
I only know of structural failures leading to bail-outs in factory
test-flights and in older wooden gliders who had been previously repaired
using unknown techniques, and end-up losing their tails, leading to
bail-outs.

Glider structural failures are extremely rare in real life outside of these
cases.

Structural failures affect airplanes in flight much more than gliders, the
most common reason is to end up inside a cloud without previous IFR
training, lose control and break up in flight.
For airplanes, the other cause for structural failure is aerobatic flight
coupled with metal fatigue.

None of these two factors are very likely in the world of Soaring, hence,
for those scared flyers out there :
Gliders don't break-up in flight unless they hit something.

f.blair

June 12th 04, 09:57 PM

I beg to differ with this last post. In a contest flight south of
Littlefield, TX in 1988, the tail section of my Open Cirrus broke just in
front of the horizontal stabilizer. At the nose of the glider went down
with no response from the stick, I began to unbuckle. As the glider went
inverted, I rolled out and successfully reached the ground with the help of
my big round parachute. I had encountered some severe turbulence, that in
later discussions with Dick Johnson, he decided must have been some type of
horizontal, rotor type cloud. I was encountering severe updrafts then
severe downdrafts. The whole glider was going up then down, not just the
nose. I was basically just holding on waiting for it to stop. Went through
about 5-6 cycles of up then down, then it got real quiet and the nose
started down and that was when I realized that the control stick did
nothing, so I got out. The boom was broken, but the tail was attached by
cables and a push rod. I watched it land in the field next to me, a smooth,
flat approach. The glider was inverted, but the tail section was upright.
The only thing that was not bent during the landing was the T.E. probe that
was on the front edge of the vertical stabilizer. Gliders can have
structural failures.

It is not a good idea to say that 'something' will never happen.

Still flying and loving it.

Fred Blair
Greater Houston Soaring Association

Original Post:
> Forget all the "I think this", "I think that" very common to
rec.aviation.soaring.

> Gliders don't fall appart in flight by themselves like ultralights and
other
> crazy flying machines.
> Gliders are, after all, certified aircraft.
>
> Sure a parachute might also save you in case of structural failure, but
the
> vast majority of bail-outs were motivated by mid-air collisions.
> I only know of structural failures leading to bail-outs in factory
> test-flights and in older wooden gliders who had been previously repaired
> using unknown techniques, and end-up losing their tails, leading to
> bail-outs.
>
> Glider structural failures are extremely rare in real life outside of
these
> cases.
>
> Gliders don't break-up in flight unless they hit something.

Gldcomp

June 13th 04, 12:42 AM

Like I said, accidents like this are extremely rare.
If we look at the history of your old Open Cirrus, it probably had previous
damage history.
It wouldn't be a surprise if it had previously severed the tailcone in a
groundloop during an outlanding.
I know a few cases similar to yours, and all could be traced back to a
previous damage that was hidden and not well repaired.

Still, a rare event, and like I said, it is NOT the reason we wear a
parachute.
Airplanes break up in flight more often than gliders and power
pilots/passengers are not required to wear a parachute.

If we respect our flight envelopes, gliders don't break up in flight.
They are certified aircraft and are designed to withstand severe forces, as
long as we respect their limits.

"f.blair" > wrote in message
news:27Kyc.16387$2i5.5757@attbi_s52...
> I beg to differ with this last post. In a contest flight south of
> Littlefield, TX in 1988, the tail section of my Open Cirrus broke just in
> front of the horizontal stabilizer. At the nose of the glider went down
> with no response from the stick, I began to unbuckle. As the glider went
> inverted, I rolled out and successfully reached the ground with the help
of
> my big round parachute. I had encountered some severe turbulence, that in
> later discussions with Dick Johnson, he decided must have been some type
of
> horizontal, rotor type cloud. I was encountering severe updrafts then
> severe downdrafts. The whole glider was going up then down, not just the
> nose. I was basically just holding on waiting for it to stop. Went
through
> about 5-6 cycles of up then down, then it got real quiet and the nose
> started down and that was when I realized that the control stick did
> nothing, so I got out. The boom was broken, but the tail was attached by
> cables and a push rod. I watched it land in the field next to me, a
smooth,
> flat approach. The glider was inverted, but the tail section was upright.
> The only thing that was not bent during the landing was the T.E. probe
that
> was on the front edge of the vertical stabilizer. Gliders can have
> structural failures.
>
> It is not a good idea to say that 'something' will never happen.
>
> Still flying and loving it.
>
> Fred Blair
> Greater Houston Soaring Association
>
> Original Post:
> > Forget all the "I think this", "I think that" very common to
> rec.aviation.soaring.
>
> > Gliders don't fall appart in flight by themselves like ultralights and
> other
> > crazy flying machines.
> > Gliders are, after all, certified aircraft.
> >
> > Sure a parachute might also save you in case of structural failure, but
> the
> > vast majority of bail-outs were motivated by mid-air collisions.
> > I only know of structural failures leading to bail-outs in factory
> > test-flights and in older wooden gliders who had been previously
repaired
> > using unknown techniques, and end-up losing their tails, leading to
> > bail-outs.
> >
> > Glider structural failures are extremely rare in real life outside of
> these
> > cases.
> >
> > Gliders don't break-up in flight unless they hit something.
>
>
>
>

Bill Daniels

June 13th 04, 01:04 AM

When I read Fred's report of tail separation, my first thought was
pre-existing damage from a tail dolly that clamped the tail boom too
tightly. The hard landing/poor repair scenario works too.

Bill Daniels

"Gldcomp" > wrote in message
. com...
> Like I said, accidents like this are extremely rare.
> If we look at the history of your old Open Cirrus, it probably had
previous
> damage history.
> It wouldn't be a surprise if it had previously severed the tailcone in a
> groundloop during an outlanding.
> I know a few cases similar to yours, and all could be traced back to a
> previous damage that was hidden and not well repaired.
>
> Still, a rare event, and like I said, it is NOT the reason we wear a
> parachute.
> Airplanes break up in flight more often than gliders and power
> pilots/passengers are not required to wear a parachute.
>
> If we respect our flight envelopes, gliders don't break up in flight.
> They are certified aircraft and are designed to withstand severe forces,
as
> long as we respect their limits.
>
> "f.blair" > wrote in message
> news:27Kyc.16387$2i5.5757@attbi_s52...
> > I beg to differ with this last post. In a contest flight south of
> > Littlefield, TX in 1988, the tail section of my Open Cirrus broke just
in
> > front of the horizontal stabilizer. At the nose of the glider went down
> > with no response from the stick, I began to unbuckle. As the glider
went
> > inverted, I rolled out and successfully reached the ground with the help
> of
> > my big round parachute. I had encountered some severe turbulence, that
in
> > later discussions with Dick Johnson, he decided must have been some type
> of
> > horizontal, rotor type cloud. I was encountering severe updrafts then
> > severe downdrafts. The whole glider was going up then down, not just
the
> > nose. I was basically just holding on waiting for it to stop. Went
> through
> > about 5-6 cycles of up then down, then it got real quiet and the nose
> > started down and that was when I realized that the control stick did
> > nothing, so I got out. The boom was broken, but the tail was attached
by
> > cables and a push rod. I watched it land in the field next to me, a
> smooth,
> > flat approach. The glider was inverted, but the tail section was
upright.
> > The only thing that was not bent during the landing was the T.E. probe
> that
> > was on the front edge of the vertical stabilizer. Gliders can have
> > structural failures.
> >
> > It is not a good idea to say that 'something' will never happen.
> >
> > Still flying and loving it.
> >
> > Fred Blair
> > Greater Houston Soaring Association
> >
> > Original Post:
> > > Forget all the "I think this", "I think that" very common to
> > rec.aviation.soaring.
> >
> > > Gliders don't fall appart in flight by themselves like ultralights and
> > other
> > > crazy flying machines.
> > > Gliders are, after all, certified aircraft.
> > >
> > > Sure a parachute might also save you in case of structural failure,
but
> > the
> > > vast majority of bail-outs were motivated by mid-air collisions.
> > > I only know of structural failures leading to bail-outs in factory
> > > test-flights and in older wooden gliders who had been previously
> repaired
> > > using unknown techniques, and end-up losing their tails, leading to
> > > bail-outs.
> > >
> > > Glider structural failures are extremely rare in real life outside of
> > these
> > > cases.
> > >
> > > Gliders don't break-up in flight unless they hit something.
> >
> >
> >
> >
>
>

Finbar

June 13th 04, 05:43 PM

Gldcomp wrote:

>OF COURSE the rare bail-outs are motivated by collision.
>Gliders don't fall appart in flight by themselves like ultralights
and other
>crazy flying machines.
>Gliders are, after all, certified aircraft.

Really? Actually, midair structural failure (usually due to pilot
error) is much more common than midair collision (arguably always due
to pilot error) as a cause of fatal accidents (which is what the
following data are from). I can't think of any obvious reason why
there would be a bias making midairs more surviveable.

This is from a previous post on causes of fatal accidents.

-------------------------------------------------

People have done these studies often enough before, but the breakdown
of fatal accident causes is worth looking at.

I looked at 61 fatal accidents that occurred between 1990 and 2002.

12 accidents, or 20%, resulted from a stall (with or without spin) in
the landing approach.

There were 11 incidents (18%) of collision with terrain during the
in-flight phase, generally along ridgelines. 3 of these were observed
to involve stalling low above the ridgeline; most of the others were
not observed.

An astonishing 9 incidents, or 15%, resulted from in-flight structural
failures. Most involved main spar failure, usually with at least one
wing separating from the fuselage, apparently as a result of
over-stressing the aircraft in flight. 2, however, involved in-flight
control system failures; one where the control stick apparently broke
off (as I understand the report) and one where a swage on one of the
control cables failed.

5 incidents, 8%, resulted from the pilot being incapacitated by heart
attack, stroke, epileptic seizure, drug use, and one apparent
incapacitation of unknown cause (aircraft simply flew into the
ground).

Another 5 incidents resulted from spins from altitude without
recovery. These are difficult to explain, especially since some of
the pilots were highly experienced. However, one high-spin glider had
its CG clearly aft of limits.

There were 4 incidents each of
- elevator/tailplane not connected
- stall on takeoff (premature termination of tow or self-launch)
- collision with terrain while attempting to land (3 of the 4 were
landouts)

There were 2 incidents each of
- midair collision
- loss of control on takeoff
- pilot killed by wire during landing

And there was one incident in which it is clear the pilot attempted to
bail out (for reasons unknown) but was apparently incapacitated when
struck by the canopy.

Here are the things that struck me:

1. Sure enough, we have lots of landing-phase stall/spin fatalities
2. Reading between the lines a little, we probably have a very similar
number of ridge-soaring fatalities.
3. We don't talk much about overstressing the aircraft, but there's a
great deal of that going on.
4. Distraction seems to be a really big issue: if you lump the landing
phase and takeoff phase stall/spins together you get the picture.
Often (PTT, landout) the cause of the distraction is fairly obvious.
5. Sometimes it's just a day with your name on it: whether it's a
heart attack, a powerline or fence you didn't see, or a wire swage
(essentially un-inspectable) that fails. "Fate comes calling"
accidents seem to be about 20% of fatalities.

Gldcomp

June 13th 04, 07:13 PM

Maybe I need to clarify this in other words.
No legislative requirement was ever established to carry parachutes because
airplanes or gliders fall appart in normal flight.
This is a common beginner's instinctive fear, expecially during a recovery
from stall, that the wings will fold and they will drop down like a rock.
Some people get so stressed out and terrorized by the sensation of G's that
they will forever avoid more than 30 degrees of bank so they don't have to
tackle the Gs. There are a lot of pilots like that.
The simple truth is that airplanes and gliders don't do that, UNLESS WE FLY
OUTSIDE THE ENVELOPE (exceed VNE, G-loads, etc), or we sabotage it in some
other fashion such as an ill-executed repair, or controls not properly
connected upon assembly.

I never said one is more survivable than the other.
Notice again what I said : Structural failures is NOT the reason we are
required to wear parachutes (but of course, if they do occur, parachutes
will save the pilot just as well).

Midair Collision is the reason we are required to wear parachutes.
That's all I said.

"Finbar" > wrote in message
om...
> Gldcomp wrote:
>
> >OF COURSE the rare bail-outs are motivated by collision.
> >Gliders don't fall appart in flight by themselves like ultralights
> and other
> >crazy flying machines.
> >Gliders are, after all, certified aircraft.
>
> Really? Actually, midair structural failure (usually due to pilot
> error) is much more common than midair collision (arguably always due
> to pilot error) as a cause of fatal accidents (which is what the
> following data are from). I can't think of any obvious reason why
> there would be a bias making midairs more surviveable.
>
> This is from a previous post on causes of fatal accidents.
>
> -------------------------------------------------
>
> People have done these studies often enough before, but the breakdown
> of fatal accident causes is worth looking at.
>
> I looked at 61 fatal accidents that occurred between 1990 and 2002.
>
> 12 accidents, or 20%, resulted from a stall (with or without spin) in
> the landing approach.
>
> There were 11 incidents (18%) of collision with terrain during the
> in-flight phase, generally along ridgelines. 3 of these were observed
> to involve stalling low above the ridgeline; most of the others were
> not observed.
>
> An astonishing 9 incidents, or 15%, resulted from in-flight structural
> failures. Most involved main spar failure, usually with at least one
> wing separating from the fuselage, apparently as a result of
> over-stressing the aircraft in flight. 2, however, involved in-flight
> control system failures; one where the control stick apparently broke
> off (as I understand the report) and one where a swage on one of the
> control cables failed.
>
> 5 incidents, 8%, resulted from the pilot being incapacitated by heart
> attack, stroke, epileptic seizure, drug use, and one apparent
> incapacitation of unknown cause (aircraft simply flew into the
> ground).
>
> Another 5 incidents resulted from spins from altitude without
> recovery. These are difficult to explain, especially since some of
> the pilots were highly experienced. However, one high-spin glider had
> its CG clearly aft of limits.
>
> There were 4 incidents each of
> - elevator/tailplane not connected
> - stall on takeoff (premature termination of tow or self-launch)
> - collision with terrain while attempting to land (3 of the 4 were
> landouts)
>
> There were 2 incidents each of
> - midair collision
> - loss of control on takeoff
> - pilot killed by wire during landing
>
> And there was one incident in which it is clear the pilot attempted to
> bail out (for reasons unknown) but was apparently incapacitated when
> struck by the canopy.
>
> Here are the things that struck me:
>
> 1. Sure enough, we have lots of landing-phase stall/spin fatalities
> 2. Reading between the lines a little, we probably have a very similar
> number of ridge-soaring fatalities.
> 3. We don't talk much about overstressing the aircraft, but there's a
> great deal of that going on.
> 4. Distraction seems to be a really big issue: if you lump the landing
> phase and takeoff phase stall/spins together you get the picture.
> Often (PTT, landout) the cause of the distraction is fairly obvious.
> 5. Sometimes it's just a day with your name on it: whether it's a
> heart attack, a powerline or fence you didn't see, or a wire swage
> (essentially un-inspectable) that fails. "Fate comes calling"
> accidents seem to be about 20% of fatalities.

Bruce Greeff

June 13th 04, 09:33 PM

Let's introduce some common sense here.

Things can break, collide or in other ways ruin your day. We wear parachutes in
the hope that, one day, should we need to rely on something to save our lives
from a no longer flyable glider, the parachute might do the job. Who cares what
the most common cause of failure is, when considering using a primary safety device.

Some points -
My 33 year old Schempp-hirth glider is under 3000 hours total time (+-2200 at
present)- officially a toddler given the life extensions to 12000. I wonder how
many bits of damage and out of spec things there are on her. She has led an
eventful, "competition plane" life for the first decade of flying. Then spent
years being somewhat neglected and inexpertly flown by a succession of owners
who could only afford a cheap glider. And cheap maintenance I suspect...

I maintain the airframe carefully, inspect and renew what looks tired. I have
had it serviced by the professionals, who rate it as one of the best they have
seen - but I really can't be sure there is no problem lying undetected.

Pilots make mistakes, one of the most experienced pilots I have known wrecked a
Ventus A by getting too close to a CB. He used full airbrake, undercarriage out
and nose progressively steeper. Eventually the elevator folded gracefully onto
the fin. His comment was that, as he kneeled on the seat, it struck him that it
was seven years since he had packed his chute. He wondered if it would open.

Some years ago in Germany a pilot landed after three hours in his Spaatz. The
parachute was uncomfortable, and he discarded it before launching again. Half an
hour later he executed a loop, without noticing my friend and a passenger above
him. They pulled up, but he struck their fuselage with his wingtip - inverted.
Wood and fabric wingtip against steel frame had predictable results. They
watched the Spaatz spiral down from nearly 5000' AGL. He did not survive the impact.

My Pioneer 29' tri-conical flies with me, every time - lumps and all. And yes
that does include flights over five hours. It is 18 years old and getting due
for replacement, and has only ever been open in the riggers shop - personally I
like it that way. But maybe some day I get unlucky, or do something stupid.
Maybe some day it will save my life.

Gldcomp wrote:
> Maybe I need to clarify this in other words.
> No legislative requirement was ever established to carry parachutes because
> airplanes or gliders fall appart in normal flight.
> This is a common beginner's instinctive fear, expecially during a recovery
> from stall, that the wings will fold and they will drop down like a rock.
> Some people get so stressed out and terrorized by the sensation of G's that
> they will forever avoid more than 30 degrees of bank so they don't have to
> tackle the Gs. There are a lot of pilots like that.
> The simple truth is that airplanes and gliders don't do that, UNLESS WE FLY
> OUTSIDE THE ENVELOPE (exceed VNE, G-loads, etc), or we sabotage it in some
> other fashion such as an ill-executed repair, or controls not properly
> connected upon assembly.
>
> I never said one is more survivable than the other.
> Notice again what I said : Structural failures is NOT the reason we are
> required to wear parachutes (but of course, if they do occur, parachutes
> will save the pilot just as well).
>
> Midair Collision is the reason we are required to wear parachutes.
> That's all I said.
>
>
> "Finbar" > wrote in message
> om...
>
>>Gldcomp wrote:
>>
>>
>>>OF COURSE the rare bail-outs are motivated by collision.
>>>Gliders don't fall appart in flight by themselves like ultralights
>>
>>and other
>>
>>>crazy flying machines.
>>>Gliders are, after all, certified aircraft.
>>
>>Really? Actually, midair structural failure (usually due to pilot
>>error) is much more common than midair collision (arguably always due
>>to pilot error) as a cause of fatal accidents (which is what the
>>following data are from). I can't think of any obvious reason why
>>there would be a bias making midairs more surviveable.
>>
>>This is from a previous post on causes of fatal accidents.
>>
>>-------------------------------------------------
>>
>>People have done these studies often enough before, but the breakdown
>>of fatal accident causes is worth looking at.
>>
>>I looked at 61 fatal accidents that occurred between 1990 and 2002.
>>
>>12 accidents, or 20%, resulted from a stall (with or without spin) in
>>the landing approach.
>>
>>There were 11 incidents (18%) of collision with terrain during the
>>in-flight phase, generally along ridgelines. 3 of these were observed
>>to involve stalling low above the ridgeline; most of the others were
>>not observed.
>>
>>An astonishing 9 incidents, or 15%, resulted from in-flight structural
>>failures. Most involved main spar failure, usually with at least one
>>wing separating from the fuselage, apparently as a result of
>>over-stressing the aircraft in flight. 2, however, involved in-flight
>>control system failures; one where the control stick apparently broke
>>off (as I understand the report) and one where a swage on one of the
>>control cables failed.
>>
>>5 incidents, 8%, resulted from the pilot being incapacitated by heart
>>attack, stroke, epileptic seizure, drug use, and one apparent
>>incapacitation of unknown cause (aircraft simply flew into the
>>ground).
>>
>>Another 5 incidents resulted from spins from altitude without
>>recovery. These are difficult to explain, especially since some of
>>the pilots were highly experienced. However, one high-spin glider had
>>its CG clearly aft of limits.
>>
>>There were 4 incidents each of
>> - elevator/tailplane not connected
>> - stall on takeoff (premature termination of tow or self-launch)
>> - collision with terrain while attempting to land (3 of the 4 were
>>landouts)
>>
>>There were 2 incidents each of
>> - midair collision
>> - loss of control on takeoff
>> - pilot killed by wire during landing
>>
>>And there was one incident in which it is clear the pilot attempted to
>>bail out (for reasons unknown) but was apparently incapacitated when
>>struck by the canopy.
>>
>>Here are the things that struck me:
>>
>>1. Sure enough, we have lots of landing-phase stall/spin fatalities
>>2. Reading between the lines a little, we probably have a very similar
>>number of ridge-soaring fatalities.
>>3. We don't talk much about overstressing the aircraft, but there's a
>>great deal of that going on.
>>4. Distraction seems to be a really big issue: if you lump the landing
>>phase and takeoff phase stall/spins together you get the picture.
>>Often (PTT, landout) the cause of the distraction is fairly obvious.
>>5. Sometimes it's just a day with your name on it: whether it's a
>>heart attack, a powerline or fence you didn't see, or a wire swage
>>(essentially un-inspectable) that fails. "Fate comes calling"
>>accidents seem to be about 20% of fatalities.
>
>
>

Gldcomp

June 13th 04, 09:58 PM

Exactly, I couldn't agree more, the parachute may save you in many different
situations.
Most of them are not the reason we are required to wear them, otherwise,
power pilots and passengers would be required to wear one too.

BTW, I've never heard of anything like this before with a glass ship :
an elevator folding gracefully onto the fin...

I've flown in front of CBs most of my flying career and never once had to
fly outside the envelope.
But that aside... an elevator folding ?? it probably was damaged before and
not well repaired.

Has this accident been listed anywhere on the Web so that we could all look
at it ?

"Bruce Greeff" > wrote in message
...
>(................................)
> Pilots make mistakes, one of the most experienced pilots I have known
wrecked a
> Ventus A by getting too close to a CB. He used full airbrake,
undercarriage out
> and nose progressively steeper. Eventually the elevator folded gracefully
onto
> the fin. (...................................)

> Gldcomp wrote:
> > Maybe I need to clarify this in other words.
> > No legislative requirement was ever established to carry parachutes
because
> > airplanes or gliders fall appart in normal flight.
> > This is a common beginner's instinctive fear, expecially during a
recovery
> > from stall, that the wings will fold and they will drop down like a
rock.
> > Some people get so stressed out and terrorized by the sensation of G's
that
> > they will forever avoid more than 30 degrees of bank so they don't have
to
> > tackle the Gs. There are a lot of pilots like that.
> > The simple truth is that airplanes and gliders don't do that, UNLESS WE
FLY
> > OUTSIDE THE ENVELOPE (exceed VNE, G-loads, etc), or we sabotage it in
some
> > other fashion such as an ill-executed repair, or controls not properly
> > connected upon assembly.
> >
> > I never said one is more survivable than the other.
> > Notice again what I said : Structural failures is NOT the reason we are
> > required to wear parachutes (but of course, if they do occur, parachutes
> > will save the pilot just as well).
> >
> > Midair Collision is the reason we are required to wear parachutes.
> > That's all I said.

Finbar

June 13th 04, 11:35 PM

"Gldcomp" > wrote in message >...
> Maybe I need to clarify this in other words.
> No legislative requirement was ever established to carry parachutes because
> airplanes or gliders fall appart in normal flight.

Actually, the only legislative requirement (in the US, at least) to
carry parachutes is precisely because of the possibility of airplanes
or gliders falling apart in flight. You're right, it doesn't relate
to normal flight: it relates to flight with a bank angle exceeding 60
degrees or a pitch angle exceeding 30 degrees (nose up or down). If
only normal flight is intended, there's no legislative requirement to
carry a parachute at all.

> This is a common beginner's instinctive fear, expecially during a recovery
> from stall, that the wings will fold and they will drop down like a rock.

Agreed.

> The simple truth is that airplanes and gliders don't do that, UNLESS WE FLY
> OUTSIDE THE ENVELOPE (exceed VNE, G-loads, etc), or we sabotage it in some
> other fashion such as an ill-executed repair, or controls not properly
> connected upon assembly.

Sort of circular definition: if everything is as it's supposed to be,
nothing happens that shouldn't. But what you said a few posts back
was,

"Gliders don't fall appart in flight by themselves like ultralights
and other
crazy flying machines. Gliders are, after all, certified aircraft."

The safety doesn't come from certification, nor from disparaging other
aircraft, nor from hiding behind legislation. It comes from
respecting the engineering limits of the aircraft. Fly your glider
normally, within its normal flight parameters and, if it was properly
engineered and maintained, it will not come apart in flight. This is
also true of "ultralights and other crazy flying machines," by which I
assume you're referring to Sparrowhawks and helicopters in that order
;-) Certification does have value: it establishes that the aircraft's
design and construction, and its operating limitations, conform to
established engineering practices. Many non-certificated aircraft
also conform to those practices, but you have to find another way to
be sure of that. In either case, you have to maintain and operate
them properly also. Properly engineered and maintained aircraft,
flown within their limits, won't fall apart in flight.

>
> I never said one is more survivable than the other.

I didn't mean to suggest you had. I made the remark because I was
comparing fatal accident statistics. If one was more surviveable,
then my statistics would not be representative of structural failures
and midair collisions as a whole. However, I think they probably are,
in which case in-flight structural failures for any reason other than
collision are 4 - 5 TIMES more likely than in-flight structural
failures due to midair collisions.

> Notice again what I said : Structural failures is NOT the reason we are
> required to wear parachutes (but of course, if they do occur, parachutes
> will save the pilot just as well).
>
> Midair Collision is the reason we are required to wear parachutes.
> That's all I said.
>
>

Yes, and it's not in accordance with the facts. Let's review.

1. Structural failures in flight are extremely rare, as I'm sure you'd
agree. With even more incredibly rare exceptions relating to
maintenance, they are almost always caused by operating the aircraft
outside its design limits - either in terms of airspeed or aerodynamic
acceleration loads - or by imposing excessive structural loads during
a midair collision.

2. Midair collisions account for about 1 in 5 in-flight structural
failures. The rest occur for reasons other than midair collision.
Therefore, to the extent that we need to worry about in-flight
structural failure at all, collision is not the primary thing to worry
about: operating the aircraft within its normal limits is.

3. The FAA does require parachutes for "aerobatic" maneuvers,
precisely because of the increased risk of structural failure
resulting from exceeding airspeed or aerodynamic acceleration limits.
It does not require parachutes because of midair collision risks.

4. Glider contest organizers (not legislators) require parachutes
because of the risk of midair collision in high-density thermaling
situations.

For our beginner friend, the bottom line is this:

Yes, most of us wear parachutes, and it seems like a rather
conservative but sensible safety precaution. We do it because we're
aware that soaring brings us into thermals that may have other gliders
in them, increasing the risk of midair collisions. However, this is
mostly just something to make us all feel better, because actual
midair collisions that cause the aircraft to become uncontrollable are
even more rare than the aircraft breaking up in flight for some other
reason - and that's very, very, very rare!

tango4

June 14th 04, 04:54 AM

Q - Do gliders 'crash', break or collide?

A- Yes

Q - Could a parachute save the pilot in some of those incidents?

A - Yes

Conclusion - Wear a 'chute!

Q - But do I have to wear a chute legally?

A - Who gives a damn! It's just the *sensible* thing to do!

Ian

"." > wrote in message
om...
> I went for a ride in a glider many years ago and was immediately taken
with
> the whole experience. I have always wanted to fly and now have the time
to
> do it as I am finished with my skydiving career. Before I sell my rigs I
> wanted to ask a question. Do any of you wear pilot rigs? Before I trade
> some gear for a pilot rig....what is the reality of actually getting out
of
> a glider if you have a structural failure or something catastrophic? I am
a
> realist and can accept the fact there are inherent risks up there believe
> me, but I don't want to buy a rig if it's a mute point. Do any of you
wear
> rigs? Thanks for the advice.
>
>

Bruce Greeff

June 14th 04, 11:40 AM

Gldcomp wrote:
> Exactly, I couldn't agree more, the parachute may save you in many different
> situations.
> Most of them are not the reason we are required to wear them, otherwise,
> power pilots and passengers would be required to wear one too.
>
> BTW, I've never heard of anything like this before with a glass ship :
> an elevator folding gracefully onto the fin...
>
> I've flown in front of CBs most of my flying career and never once had to
> fly outside the envelope.
> But that aside... an elevator folding ?? it probably was damaged before and
> not well repaired.
>
<Big snip>

By his own admission he was so far past Vne I don't think it appropriate to
consider structural defect. The aircraft was virtually new as I understand it -
and a new design at the time. (so the crash was not reported on the internet.)

The failure mode of most elevators at speeds exceeding Vne will be downwards.

Why he flew close enough to a CB that he was unable to avoid it while remaining
inside the envelope is anybodies guess.

Bert Willing

June 14th 04, 02:04 PM

That doesn't make sense to me. At high speeds, the elevator produces lift so
in case of structural failure, the bits would go upwards.

--
Bert Willing

ASW20 "TW"

"Bruce Greeff" > a écrit dans le message de
...

> The failure mode of most elevators at speeds exceeding Vne will be
downwards.
>

Gldcomp

June 14th 04, 11:40 PM

"Bert Willing" > wrote in
message ...
> That doesn't make sense to me. At high speeds, the elevator produces lift
so
> in case of structural failure, the bits would go upwards.
>
> --
> Bert Willing
>
> ASW20 "TW"
>
Bert,

The elevator does produce lift, but in the opposite direction as the wings
(most of the time anyway).

Bert Willing

June 15th 04, 08:43 AM

You're right - the elevator produces lift (same direction as the wings) at
low speeds, not at high speeds. Got mixed up.

--
Bert Willing

ASW20 "TW"

"Gldcomp" > a écrit dans le message de
om...
> "Bert Willing" > wrote in
> message ...
> > That doesn't make sense to me. At high speeds, the elevator produces
lift
> so
> > in case of structural failure, the bits would go upwards.
> >
> > --
> > Bert Willing
> >
> > ASW20 "TW"
> >
> Bert,
>
> The elevator does produce lift, but in the opposite direction as the wings
> (most of the time anyway).
>
>

Gldcomp

June 15th 04, 03:03 PM

Bert,

It has little to do with airspeed. The position of the CG will determine the
force on the elevator.

"Bert Willing" > wrote in
message ...
> You're right - the elevator produces lift (same direction as the wings) at
> low speeds, not at high speeds. Got mixed up.
>
> --
> Bert Willing
>
> ASW20 "TW"
>
>
> "Gldcomp" > a écrit dans le message de
> om...
> > "Bert Willing" > wrote in
> > message ...
> > > That doesn't make sense to me. At high speeds, the elevator produces
> lift
> > so
> > > in case of structural failure, the bits would go upwards.
> > >
> > > --
> > > Bert Willing
> > >
> > > ASW20 "TW"
> > >
> > Bert,
> >
> > The elevator does produce lift, but in the opposite direction as the
wings
> > (most of the time anyway).
> >
> >
>
>

Bert Willing

June 15th 04, 04:07 PM

Not quite correct. At high angles of attack, the elevator produces lift and
at of angle of attack, it produces negative lift. The crossover (i.e. zero
lift, minimum drag) is a design criterium and is usually placed at the max
L/D angle of attack. But then, this will of course be influenced by a large
variation of the CG.

--
Bert Willing

ASW20 "TW"

"Gldcomp" > a écrit dans le message de
. com...
> Bert,
>
> It has little to do with airspeed. The position of the CG will determine
the
> force on the elevator.
>
>
> "Bert Willing" > wrote in
> message ...
> > You're right - the elevator produces lift (same direction as the wings)
at
> > low speeds, not at high speeds. Got mixed up.
> >
> > --
> > Bert Willing
> >
> > ASW20 "TW"
> >
> >
> > "Gldcomp" > a écrit dans le message de
> > om...
> > > "Bert Willing" > wrote
in
> > > message ...
> > > > That doesn't make sense to me. At high speeds, the elevator produces
> > lift
> > > so
> > > > in case of structural failure, the bits would go upwards.
> > > >
> > > > --
> > > > Bert Willing
> > > >
> > > > ASW20 "TW"
> > > >
> > > Bert,
> > >
> > > The elevator does produce lift, but in the opposite direction as the
> wings
> > > (most of the time anyway).
> > >
> > >
> >
> >
>
>

Andy Durbin

June 15th 04, 05:56 PM

"Bert Willing" > wrote in message >...
> You're right - the elevator produces lift (same direction as the wings) at
> low speeds, not at high speeds. Got mixed up.
>
> --
> Bert Willing
>
> ASW20 "TW"
>
>
> "Gldcomp" > a écrit dans le message de
> om...
> > "Bert Willing" > wrote in
> > message ...
> > > That doesn't make sense to me. At high speeds, the elevator produces
> lift
> so
> > > in case of structural failure, the bits would go upwards.
> > >
> > > --
> > > Bert Willing
> > >
> > > ASW20 "TW"
> > >
> > Bert,
> >
> > The elevator does produce lift, but in the opposite direction as the wings
> > (most of the time anyway).
> >
> >

Ok, so let me see if I've got this straight now. I cruising along at
60 kts in trim and elevator close to neutral. I want to go 140kts so
I push the stick forward, the elevator goes down, which pushes the
tail up, which pushes the nose goes down, I go faster. And all this is
because the elevator is producing more lift in the downward direction?

For a fixed stab with moving elevator don't we have to consider the
forces on both components separately to predict the failure mode?

Andy

John Giddy

June 15th 04, 10:22 PM

Andy Durbin wrote:
> "Bert Willing" > wrote
> in message >...
>> You're right - the elevator produces lift (same direction as the
>> wings) at low speeds, not at high speeds. Got mixed up.
>>
>> --
>> Bert Willing
>>
>> ASW20 "TW"
>>
>>
>> "Gldcomp" > a écrit dans le message de
>> om...
>>> "Bert Willing" >
>>> wrote in message ...
>>>> That doesn't make sense to me. At high speeds, the elevator
>>>> produces
>> lift
>> so
>>>> in case of structural failure, the bits would go upwards.
>>>>
>>>> --
>>>> Bert Willing
>>>>
>>>> ASW20 "TW"
>>>>
>>> Bert,
>>>
>>> The elevator does produce lift, but in the opposite direction as
>>> the wings (most of the time anyway).
>>>
>>>
>
> Ok, so let me see if I've got this straight now. I cruising along
at
> 60 kts in trim and elevator close to neutral. I want to go 140kts
so
> I push the stick forward, the elevator goes down, which pushes the
> tail up, which pushes the nose goes down, I go faster. And all this
is
> because the elevator is producing more lift in the downward
direction?
>
> For a fixed stab with moving elevator don't we have to consider the
> forces on both components separately to predict the failure mode?

I think we are confusing transient and steady forces here. The
overspeed problem occurs with the controls almost in neutral, but the
plane in a dive, where the speed builds up steadily. In this case the
tailplane will be generating an increasing downward force in relation
to the longitudinal axis of the aircraft. This downward force is to
counteract the forward rotation force generated by the wing. At a high
enough speed these forces will increase beyond the capacity of the
structure to support them.

The transient case is when a large control excursion is input at high
speed, and in this case the force on the tailplane could be in either
direction, depending on the direction of control input. However
downward total force is likely to be more severe in a pull-up than an
upward force in a push-over, since the contribution of the elevator
adds to the existing downward force in the first case and subtracts
from it in the push-over case.

That's my 2c worth...
Cheers, John G.

Eric Greenwell

June 16th 04, 06:23 AM

Andy Durbin wrote:

>>>The elevator does produce lift, but in the opposite direction as the wings
>>>(most of the time anyway).
>>>
>>>
>
>
> Ok, so let me see if I've got this straight now. I cruising along at
> 60 kts in trim and elevator close to neutral. I want to go 140kts so
> I push the stick forward, the elevator goes down, which pushes the
> tail up, which pushes the nose goes down, I go faster. And all this is
> because the elevator is producing more lift in the downward direction?

It is confusing! Here's what happens, simplified:

*The horizontal stabilizer (with the flap we call the "elevator") is
pushing down (at least at "higher" speeds - maybe not at 60 knots -
dependes on the glider)
*You push the stick forward
*the elevator flap goes down
*this _reduces_ the downward force of the horizontal stabilizer, but
doesn't elimanate it
*this allows the tail to rise

There is more to it than that, of course.

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

Eric Greenwell
Washington State
USA

Gldcomp

June 16th 04, 10:14 AM

Bert,

I'm sorry, you are not correct or not expressing yourself correctly.
I'm not expressing an oppinion here, I'm telling you how it is.

The CG is by design located ahead of the Neutral Point of the glider
(otherwise the glider would be uncontrollable), so, it has the overall
tendency to push the nose of the glider down, since the Neutral Point is the
place where all the Lift is acting.
To counteract this force, the tail planes are always pushing the tail DOWN,
thus keeping the forces balanced.
We vary the amount of down force produced by the tail planes by moving the
elevator with the stick.

When we move the CG aft, we bring it closer to the Neutral Point, which
reduced the required down force produced by the elevator.
In extremeley aft CG situations, the tailplanes MAY IN FACT produce an
overall UP force on the tail, but this is the exception, rather than the
rule.

The more forward the CG position, however, the more DOWN force is necessary
on the tail.
This is the very reason pilots try to place the CG aft in competition
gliders : so that the elevator doesn't have to produce quite so much DOWN
force on the tail. The result is improved climb because of this.

"Bert Willing" > wrote in
message ...
> Not quite correct. At high angles of attack, the elevator produces lift
and
> at of angle of attack, it produces negative lift. The crossover (i.e. zero
> lift, minimum drag) is a design criterium and is usually placed at the max
> L/D angle of attack. But then, this will of course be influenced by a
large
> variation of the CG.
>
> --
> Bert Willing
>
> ASW20 "TW"
>
>
> "Gldcomp" > a écrit dans le message de
> . com...
> > Bert,
> >
> > It has little to do with airspeed. The position of the CG will determine
> the
> > force on the elevator.
> >
> >
> > "Bert Willing" > wrote in
> > message ...
> > > You're right - the elevator produces lift (same direction as the
wings)
> at
> > > low speeds, not at high speeds. Got mixed up.
> > >
> > > --
> > > Bert Willing
> > >
> > > ASW20 "TW"
> > >
> > >
> > > "Gldcomp" > a écrit dans le message de
> > > om...
> > > > "Bert Willing" > wrote
> in
> > > > message ...
> > > > > That doesn't make sense to me. At high speeds, the elevator
produces
> > > lift
> > > > so
> > > > > in case of structural failure, the bits would go upwards.
> > > > >
> > > > > --
> > > > > Bert Willing
> > > > >
> > > > > ASW20 "TW"
> > > > >
> > > > Bert,
> > > >
> > > > The elevator does produce lift, but in the opposite direction as the
> > wings
> > > > (most of the time anyway).
> > > >
> > > >
> > >
> > >
> >
> >
>
>

Andreas Maurer

June 16th 04, 12:56 PM

On Wed, 16 Jun 2004 09:14:13 GMT, "Gldcomp" >
wrote:

>Bert,
>
>I'm sorry, you are not correct or not expressing yourself correctly.
>I'm not expressing an oppinion here, I'm telling you how it is.

Sorry to intrude, but Bert is correct. :)

The induced drag of a low aspect-ratio horizontal stab is
considerable, therefore the designer tries to minimize it at the speed
of max L/D - since L/D is still the main number to characterize the
performanc eof a glider, this is the number that needs to be
maximized.
The only case where induced drag is 0 is when the tail does not create
any Cl at all.

Situation at low speeds:
Don't forget that the center of pressure (CP) moves forward with
rising AoA, creating a nose-up momentum - and this needs to be
encountered by the tail (wich is therefore creating lift at speeds
below the speed of max. L/D). And vice versa.

>The more forward the CG position, however, the more DOWN force is necessary
>on the tail.
>This is the very reason pilots try to place the CG aft in competition
>gliders : so that the elevator doesn't have to produce quite so much DOWN
>force on the tail. The result is improved climb because of this.

The aerodynamical benefit of an aft CG is the fact that the tail
airfoil with upwards deflected elevator has got an extremely bad L/D
due to its negative camber. Less upwards elevator deflection (due to
aft CG) drastically improves the L/D of the tail.

Bye
Andreas

Bert Willing

June 16th 04, 12:57 PM

If you had made your statements for powered aircrafts, you would be
completely right. However, the design criterons for sailplanes are slightly
different because the airfoils used are different (well, today's airfoils
anyways).
The forces produced by the tailplane are fixed by the pitching coefficient
of the airfoil in the first place. At high angles of attack, the airfoil
pitches up which has to be compensated by a lift vector on the tailplane. As
you need to have the CG in front of the neutral point for stability reasons,
it reduces the required lift on the tailplane as the CG moves forward.

To use your words, this is not an opinion. A good textbook wood be "Concept
and design of Sailplanes" by Fred Thomas (the wording of the title may vary
as I just know the German title).

--
Bert Willing

ASW20 "TW"

"Gldcomp" > a écrit dans le message de
. com...
> Bert,
>
> I'm sorry, you are not correct or not expressing yourself correctly.
> I'm not expressing an oppinion here, I'm telling you how it is.
>
> The CG is by design located ahead of the Neutral Point of the glider
> (otherwise the glider would be uncontrollable), so, it has the overall
> tendency to push the nose of the glider down, since the Neutral Point is
the
> place where all the Lift is acting.
> To counteract this force, the tail planes are always pushing the tail
DOWN,
> thus keeping the forces balanced.
> We vary the amount of down force produced by the tail planes by moving the
> elevator with the stick.
>
> When we move the CG aft, we bring it closer to the Neutral Point, which
> reduced the required down force produced by the elevator.
> In extremeley aft CG situations, the tailplanes MAY IN FACT produce an
> overall UP force on the tail, but this is the exception, rather than the
> rule.
>
> The more forward the CG position, however, the more DOWN force is
necessary
> on the tail.
> This is the very reason pilots try to place the CG aft in competition
> gliders : so that the elevator doesn't have to produce quite so much DOWN
> force on the tail. The result is improved climb because of this.
>
>
>
> "Bert Willing" > wrote in
> message ...
> > Not quite correct. At high angles of attack, the elevator produces lift
> and
> > at of angle of attack, it produces negative lift. The crossover (i.e.
zero
> > lift, minimum drag) is a design criterium and is usually placed at the
max
> > L/D angle of attack. But then, this will of course be influenced by a
> large
> > variation of the CG.
> >
> > --
> > Bert Willing
> >
> > ASW20 "TW"
> >
> >
> > "Gldcomp" > a écrit dans le message de
> > . com...
> > > Bert,
> > >
> > > It has little to do with airspeed. The position of the CG will
determine
> > the
> > > force on the elevator.
> > >
> > >
> > > "Bert Willing" > wrote
in
> > > message ...
> > > > You're right - the elevator produces lift (same direction as the
> wings)
> > at
> > > > low speeds, not at high speeds. Got mixed up.
> > > >
> > > > --
> > > > Bert Willing
> > > >
> > > > ASW20 "TW"
> > > >
> > > >
> > > > "Gldcomp" > a écrit dans le message de
> > > > om...
> > > > > "Bert Willing" >
wrote
> > in
> > > > > message ...
> > > > > > That doesn't make sense to me. At high speeds, the elevator
> produces
> > > > lift
> > > > > so
> > > > > > in case of structural failure, the bits would go upwards.
> > > > > >
> > > > > > --
> > > > > > Bert Willing
> > > > > >
> > > > > > ASW20 "TW"
> > > > > >
> > > > > Bert,
> > > > >
> > > > > The elevator does produce lift, but in the opposite direction as
the
> > > wings
> > > > > (most of the time anyway).
> > > > >
> > > > >
> > > >
> > > >
> > >
> > >
> >
> >
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>

Bert Willing

June 16th 04, 01:00 PM

Had a look at Amazon: The Fundamentals of Sailplane Design, Fred Thomas &
Judah Milgram

--
Bert Willing

ASW20 "TW"

"Gldcomp" > a écrit dans le message de
. com...
> Bert,
>
> I'm sorry, you are not correct or not expressing yourself correctly.
> I'm not expressing an oppinion here, I'm telling you how it is.
>
> The CG is by design located ahead of the Neutral Point of the glider
> (otherwise the glider would be uncontrollable), so, it has the overall
> tendency to push the nose of the glider down, since the Neutral Point is
the
> place where all the Lift is acting.
> To counteract this force, the tail planes are always pushing the tail
DOWN,
> thus keeping the forces balanced.
> We vary the amount of down force produced by the tail planes by moving the
> elevator with the stick.
>
> When we move the CG aft, we bring it closer to the Neutral Point, which
> reduced the required down force produced by the elevator.
> In extremeley aft CG situations, the tailplanes MAY IN FACT produce an
> overall UP force on the tail, but this is the exception, rather than the
> rule.
>
> The more forward the CG position, however, the more DOWN force is
necessary
> on the tail.
> This is the very reason pilots try to place the CG aft in competition
> gliders : so that the elevator doesn't have to produce quite so much DOWN
> force on the tail. The result is improved climb because of this.
>
>
>
> "Bert Willing" > wrote in
> message ...
> > Not quite correct. At high angles of attack, the elevator produces lift
> and
> > at of angle of attack, it produces negative lift. The crossover (i.e.
zero
> > lift, minimum drag) is a design criterium and is usually placed at the
max
> > L/D angle of attack. But then, this will of course be influenced by a
> large
> > variation of the CG.
> >
> > --
> > Bert Willing
> >
> > ASW20 "TW"
> >
> >
> > "Gldcomp" > a écrit dans le message de
> > . com...
> > > Bert,
> > >
> > > It has little to do with airspeed. The position of the CG will
determine
> > the
> > > force on the elevator.
> > >
> > >
> > > "Bert Willing" > wrote
in
> > > message ...
> > > > You're right - the elevator produces lift (same direction as the
> wings)
> > at
> > > > low speeds, not at high speeds. Got mixed up.
> > > >
> > > > --
> > > > Bert Willing
> > > >
> > > > ASW20 "TW"
> > > >
> > > >
> > > > "Gldcomp" > a écrit dans le message de
> > > > om...
> > > > > "Bert Willing" >
wrote
> > in
> > > > > message ...
> > > > > > That doesn't make sense to me. At high speeds, the elevator
> produces
> > > > lift
> > > > > so
> > > > > > in case of structural failure, the bits would go upwards.
> > > > > >
> > > > > > --
> > > > > > Bert Willing
> > > > > >
> > > > > > ASW20 "TW"
> > > > > >
> > > > > Bert,
> > > > >
> > > > > The elevator does produce lift, but in the opposite direction as
the
> > > wings
> > > > > (most of the time anyway).
> > > > >
> > > > >
> > > >
> > > >
> > >
> > >
> >
> >
>
>

Andy Durbin

June 16th 04, 04:04 PM

Eric Greenwell > wrote in message > It is confusing! Here's what happens, simplified:
>
> *The horizontal stabilizer (with the flap we call the "elevator") is
> pushing down (at least at "higher" speeds - maybe not at 60 knots -
> dependes on the glider)
> *You push the stick forward
> *the elevator flap goes down
> *this _reduces_ the downward force of the horizontal stabilizer, but
> doesn't elimanate it
> *this allows the tail to rise
>
> There is more to it than that, of course.

If it is confusing it is only because a previous poster made specific
reference to elevator forces when perhaps they meant the net force
acting on the horizontal stabilizer.

Parts is parts but they all have names.

Andy

Gldcomp

June 17th 04, 06:12 AM

"Andreas Maurer" > wrote in message
...
> On Wed, 16 Jun 2004 09:14:13 GMT, "Gldcomp" >
> wrote:
>
>
> Sorry to intrude, but Bert is correct. :)
>
> The induced drag of a low aspect-ratio horizontal stab is
> considerable, therefore the designer tries to minimize it at the speed
> of max L/D - since L/D is still the main number to characterize the
> performanc eof a glider, this is the number that needs to be
> maximized.
> The only case where induced drag is 0 is when the tail does not create
> any Cl at all.
>
> Situation at low speeds:
> Don't forget that the center of pressure (CP) moves forward with
> rising AoA, creating a nose-up momentum - and this needs to be
> encountered by the tail (wich is therefore creating lift at speeds
> below the speed of max. L/D). And vice versa.

Correction : The tail is generating LESS negative lift.

> >The more forward the CG position, however, the more DOWN force is
necessary
> >on the tail.
> >This is the very reason pilots try to place the CG aft in competition
> >gliders : so that the elevator doesn't have to produce quite so much DOWN
> >force on the tail. The result is improved climb because of this.
>
> The aerodynamical benefit of an aft CG is the fact that the tail
> airfoil with upwards deflected elevator has got an extremely bad L/D
> due to its negative camber. Less upwards elevator deflection (due to
> aft CG) drastically improves the L/D of the tail.

Exactly. And this is because the tail generates less negative lift.

nowhere

June 17th 04, 06:40 AM

1: A parachute is not very expensive (relative to the other things you
may buy as you get into soaring)

2: Most ships have seats designed to take a parachute (I assume this
is a result of the fact that chutes are mandatory in contests) so you
usually either need to wear a chute or use some cushions. I have found
that in most gliders a good chute is more comfortable than cushions.

3: These points being taken into account, why would you not wear a
chute? Maybe you will never have the opportunity to use it (I
certainly hope I never do!). Maybe you wouldn't be able to get out if
you nedded to. However maybe you WILL need to bail out and maybe you
WILL be successful in doing so. No matter what happens wearing a chute
gives you another option and has no real drawbacks.

4: Just think how stupid you would feel if you DID need a chute and
didin't have one.

5: If you and your ship end up down in the wilderness and have to wait
a day or longer to get rescued all that nylon could be a useful thing
to have on hand.

If you can try out a number of different types of chutes in your
glider to find out which suits you and your ship best, do it. My club
has nearly a dozen chutes and after trying them out I bought a
National backpack because it fits perfectly into the seat recess of my
ASW15b. It's as comfortable as lying in bed! On the other hand, when
flying my club's Grobs, I used a bigger Security chute because they
raise me up a bit so I can see out better. In the backseat of our L13
and L23 I use these huge ex-military chutes we have because they raise
me up and push me forward so my head isn't as buried in the wing root
as it would be with a backpack chute.

Bert Willing

June 17th 04, 08:02 AM

As I said: get a textbook, and don't confuse powered aircraft with gliders.

--
Bert Willing

ASW20 "TW"

"Gldcomp" > a écrit dans le message de
m...
>
> "Andreas Maurer" > wrote in message
> ...
> > On Wed, 16 Jun 2004 09:14:13 GMT, "Gldcomp" >
> > wrote:
> >
> >
> > Sorry to intrude, but Bert is correct. :)
> >
> > The induced drag of a low aspect-ratio horizontal stab is
> > considerable, therefore the designer tries to minimize it at the speed
> > of max L/D - since L/D is still the main number to characterize the
> > performanc eof a glider, this is the number that needs to be
> > maximized.
> > The only case where induced drag is 0 is when the tail does not create
> > any Cl at all.
> >
> > Situation at low speeds:
> > Don't forget that the center of pressure (CP) moves forward with
> > rising AoA, creating a nose-up momentum - and this needs to be
> > encountered by the tail (wich is therefore creating lift at speeds
> > below the speed of max. L/D). And vice versa.
>
> Correction : The tail is generating LESS negative lift.
>
> > >The more forward the CG position, however, the more DOWN force is
> necessary
> > >on the tail.
> > >This is the very reason pilots try to place the CG aft in competition
> > >gliders : so that the elevator doesn't have to produce quite so much
DOWN
> > >force on the tail. The result is improved climb because of this.
> >
> > The aerodynamical benefit of an aft CG is the fact that the tail
> > airfoil with upwards deflected elevator has got an extremely bad L/D
> > due to its negative camber. Less upwards elevator deflection (due to
> > aft CG) drastically improves the L/D of the tail.
>
> Exactly. And this is because the tail generates less negative lift.
>
>

Gldcomp

June 17th 04, 09:29 AM

Bert,

You should do that yourself.
You all seem to be confusing how the forces interact.

The tailplanes can produce positive lift in extreme aft CG positions,
nothing to do with low speeds.

"Bert Willing" > wrote in
message ...
> As I said: get a textbook, and don't confuse powered aircraft with
gliders.
>
> --
> Bert Willing
>
> ASW20 "TW"
>
>
> "Gldcomp" > a écrit dans le message de
> m...
> >
> > "Andreas Maurer" > wrote in message
> > ...
> > > On Wed, 16 Jun 2004 09:14:13 GMT, "Gldcomp" >
> > > wrote:
> > >
> > >
> > > Sorry to intrude, but Bert is correct. :)
> > >
> > > The induced drag of a low aspect-ratio horizontal stab is
> > > considerable, therefore the designer tries to minimize it at the speed
> > > of max L/D - since L/D is still the main number to characterize the
> > > performanc eof a glider, this is the number that needs to be
> > > maximized.
> > > The only case where induced drag is 0 is when the tail does not create
> > > any Cl at all.
> > >
> > > Situation at low speeds:
> > > Don't forget that the center of pressure (CP) moves forward with
> > > rising AoA, creating a nose-up momentum - and this needs to be
> > > encountered by the tail (wich is therefore creating lift at speeds
> > > below the speed of max. L/D). And vice versa.
> >
> > Correction : The tail is generating LESS negative lift.
> >
> > > >The more forward the CG position, however, the more DOWN force is
> > necessary
> > > >on the tail.
> > > >This is the very reason pilots try to place the CG aft in competition
> > > >gliders : so that the elevator doesn't have to produce quite so much
> DOWN
> > > >force on the tail. The result is improved climb because of this.
> > >
> > > The aerodynamical benefit of an aft CG is the fact that the tail
> > > airfoil with upwards deflected elevator has got an extremely bad L/D
> > > due to its negative camber. Less upwards elevator deflection (due to
> > > aft CG) drastically improves the L/D of the tail.
> >
> > Exactly. And this is because the tail generates less negative lift.
> >
> >
>
>