Glider accident while filming commercial in 2011. NTSB Report updated

Bill

With all due respect - how many winch launches do you have in a Ka8?
(Substitute all sorts of very light, early high wing wood and fabric.)

At .5g, and at 1g?

Personally, I would prefer to watch than do, and I would prefer to not
have to watch either.
Have watched the over rotation with full down elevator from over
enthusiastic winch...

Been there - assume I must be an old wife.

Bruce

On 2013/07/01 5:44 PM, Bill D wrote:
Nigel, I read your post and it's mostly an "old wives tale".

Yes, gliders lower their tails which can be an issue on hard surfaces so someone holds them down as seen in the PW-5 video. On turf, it's a non-issue. However, it has nothing to do with acceleration causing premature uncommanded rotation. The tailwheel on the ground prevents it. Glider's don't "shoot into the air" or do anything else inappropriate under 1G acceleration. It's been thoroughly flight tested.

On Monday, July 1, 2013 8:58:00 AM UTC-6, Nigel Pocock wrote:
If Bill D could be bothered to read my posting before spouting a reply he

wouls see that I had started the launch with full forward stick in both

cases.

Hard acceration with these gliders can cause the tail to hit the ground

hard - not safe. To avoid this the tail of the K8s are usually held down

for the launch. Too hard acceration can cause the glider to shoot into the

air and immediately into a 45 degree climb despite the stick position. If

the rope breaks at this point you have too little height to recover. Hence

the winch driver will give slower initial acceleration with these types.

By regained control I mean the elevator having any effect. Until then you

are just a passenger.

I was always taught with ground launch to keep it straight and level until

the glider lifts off in a shallow climb. When a safe speed had been reached

to rotate steadily into a full climb. At any point in this process you can

still recover and land safely using the correct procedures - as taught be

both the german and british systems.





At 14:42 29 June 2013, Bill D wrote:

On Saturday, June 29, 2013 8:22:46 AM UTC-6, Nigel Pocock wrote:

Excessive initial ecceleration can cause problems with certain types. I

=20

have experienced it with 2 types.=20

=20

PW5 with stick fully forward at the start of the launch. Hard

acceleratio=

n

=20

caused the glider to rotate from the nose wheel to the tail wheel and

=20

rocket into the air. I only managed to regain control at about 50ft.

=20

The other one is the K8. Light glider, high wing. Similar problem.

=20

=20

=20

If slow acceleration is a safety problem what about the ground run and

ta=

ke

=20

off with aerotow using belly hooks, and autotows?



K8's and PW-5's, as with all "nose dragger's, are supposed to rotate back

o=

nto their tail wheels. What do you mean exactly by "regained control"?

Yo=

u're still with us so, presumably, it worked. With those gliders you

shoul=

d have started the ground roll with the stick full forward.



Aero tow with a CG hook isn't safe as discussed elsewhere on this forum.

H=

owever a tug can't generate the forces a winch can so a wing drop induced

g=

round loop likely won't be as severe.




--
Bruce Greeff
T59D #1771

On Tuesday, July 2, 2013 10:55:40 AM UTC-6, BruceGreeff wrote:
Bill

With all due respect - how many winch launches do you have in a Ka8?

(Substitute all sorts of very light, early high wing wood and fabric.)
At .5g, and at 1g?

100's maybe 1000's At .5G I'll complain to the winch operator asking for more acceleration since it's unsafe. 1G is much safer.

Have watched the over rotation with full down elevator from over enthusiastic winch...

I haven't and I don't believe you have either because it doesn't happen. In fact CS-22 (JAR-22) Paragraph CS 22.152(4) expressly forbids forward pressure during winch launch for gliders.

However, people THINK it happens. Google the term "head-up illusion". It says in part, quote:

"Somatogravic illusions are caused by linear accelerations effecting the utricle and the saccule of the vestibular system. The head-up illusion involves a sudden forward linear acceleration during level flight where the pilot perceives the illusion that the nose of the aircraft is pitching up."

This explains 100% of the "uncommanded pitch-up under acceleration" stories..

You guys need to stop telling each other stories and do some basic reading on the subject.

Hi Nigel,

On Mon, 01 Jul 2013 14:58:00 +0000, Nigel Pocock
wrote:

If Bill D could be bothered to read my posting before spouting a reply he
wouls see that I had started the launch with full forward stick in both
cases.

Really bad mistake. Will make you want to change your pants after you
trtied this in a glider with full-flying elevator. NO glider will take
off with the stick full nose-down if the CG is halfways right.

Hard acceration with these gliders can cause the tail to hit the ground
hard - not safe.

Safe. Happens all the time, this is what the glider is designed for.


To avoid this the tail of the K8s are usually held down
for the launch. Too hard acceration can cause the glider to shoot into the
air and immediately into a 45 degree climb despite the stick position.

Absolutely not.

If
the rope breaks at this point you have too little height to recover. Hence
the winch driver will give slower initial acceleration with these types.
By regained control I mean the elevator having any effect. Until then you
are just a passenger.

Absolutely not.



Really sorry to contradict, but the dangers you are describing are
simply not true (or, rather, caused by bad training).


Even if the tail hits the ground more or less hard (which is easy to
avoid by applying power smoothly), the glider takes off at a speed
where elevator control is always perfectly sufficient to control the
pitch up momentum. If the wing flies fast enough to lift the glider,
the elevator flies fast enough to prevent pitch up - if the elevator
is kept in the correct position.

In case you did not know this: Elevator size of at least any German
designed glider is certified (and verified) that there is always 100%
elevator authority to prevent pitch up.

If the acceleration pushes back the hand that is holding the stick
(or, by using a soft cushion, the whole pilot moves backwards), things
look differerent...


In my club we've been doing winch launches for the last 60 years now,
with about 200.000 winch launches. ***Not one single accident*** due
to the causes you describe. Hundreds of pilots,hundreds of student
pilots, hundreds of winch drivers, dozens of instructors, half a dozen
of different winches from an 120 hp V8 engines to 280 hp turbo
Diesel. Gliders range from Spatz, Ka-6, Ka-8, to ASH-25.

Not one single accident.

And no, we do not push the tails of our Ka-8s down.
I've seen morre winch launches that I care to count where the gound
run was less than 6 ft. (ft - not yards!). Naught to 40 mph in less
than a second.


*Any* too-steep winch launch that I ever saw during the last 30 years
was caused by nose-up elevator at the moment of lift off. Any.




I was always taught with ground launch to keep it straight and level until
the glider lifts off in a shallow climb. When a safe speed had been reached
to rotate steadily into a full climb. At any point in this process you can
still recover and land safely using the correct procedures - as taught be
both the german and british systems.

The German system teaches to keep the stick in the recommended
(trimmed) position. If done halfways properly, any glider will launch
itself and rotate into the climb smoothly ***without any elevator
input***.
Works like a charm for absolutely any glider, be it an L--Spatz, a
Ka-8 or a heavy ASH-25.

An absolute no-no is launching with full nose-down elevator as you are
doing it. Makes a smooth transition into the climb really hard and
often leads to over-controlling.



Cheers from Germany
Andreas


p.s.
The only case where the elevator is not able to control a nose-up
rotation of the glider is, if a full-flying elevator is pushed fully
forward, therefore stalling the complete horizontal tail.

Thanks, Andreas. I hope the Brits are reading it.


On Monday, July 1, 2013 6:33:02 PM UTC-6, Andreas Maurer wrote:
Hi Nigel,



On Mon, 01 Jul 2013 14:58:00 +0000, Nigel Pocock

wrote:



If Bill D could be bothered to read my posting before spouting a reply he

wouls see that I had started the launch with full forward stick in both

cases.



Really bad mistake. Will make you want to change your pants after you

trtied this in a glider with full-flying elevator. NO glider will take

off with the stick full nose-down if the CG is halfways right.



Hard acceration with these gliders can cause the tail to hit the ground

hard - not safe.



Safe. Happens all the time, this is what the glider is designed for.





To avoid this the tail of the K8s are usually held down

for the launch. Too hard acceration can cause the glider to shoot into the

air and immediately into a 45 degree climb despite the stick position.



Absolutely not.



If

the rope breaks at this point you have too little height to recover. Hence

the winch driver will give slower initial acceleration with these types.

By regained control I mean the elevator having any effect. Until then you

are just a passenger.



Absolutely not.







Really sorry to contradict, but the dangers you are describing are

simply not true (or, rather, caused by bad training).





Even if the tail hits the ground more or less hard (which is easy to

avoid by applying power smoothly), the glider takes off at a speed

where elevator control is always perfectly sufficient to control the

pitch up momentum. If the wing flies fast enough to lift the glider,

the elevator flies fast enough to prevent pitch up - if the elevator

is kept in the correct position.



In case you did not know this: Elevator size of at least any German

designed glider is certified (and verified) that there is always 100%

elevator authority to prevent pitch up.



If the acceleration pushes back the hand that is holding the stick

(or, by using a soft cushion, the whole pilot moves backwards), things

look differerent...





In my club we've been doing winch launches for the last 60 years now,

with about 200.000 winch launches. ***Not one single accident*** due

to the causes you describe. Hundreds of pilots,hundreds of student

pilots, hundreds of winch drivers, dozens of instructors, half a dozen

of different winches from an 120 hp V8 engines to 280 hp turbo

Diesel. Gliders range from Spatz, Ka-6, Ka-8, to ASH-25.



Not one single accident.



And no, we do not push the tails of our Ka-8s down.

I've seen morre winch launches that I care to count where the gound

run was less than 6 ft. (ft - not yards!). Naught to 40 mph in less

than a second.





*Any* too-steep winch launch that I ever saw during the last 30 years

was caused by nose-up elevator at the moment of lift off. Any.









I was always taught with ground launch to keep it straight and level until

the glider lifts off in a shallow climb. When a safe speed had been reached

to rotate steadily into a full climb. At any point in this process you can

still recover and land safely using the correct procedures - as taught be

both the german and british systems.



The German system teaches to keep the stick in the recommended

(trimmed) position. If done halfways properly, any glider will launch

itself and rotate into the climb smoothly ***without any elevator

input***.

Works like a charm for absolutely any glider, be it an L--Spatz, a

Ka-8 or a heavy ASH-25.



An absolute no-no is launching with full nose-down elevator as you are

doing it. Makes a smooth transition into the climb really hard and

often leads to over-controlling.







Cheers from Germany

Andreas





p.s.

The only case where the elevator is not able to control a nose-up

rotation of the glider is, if a full-flying elevator is pushed fully

forward, therefore stalling the complete horizontal tail.

I have in excess of 4000 winch launches in many types of Glider includung
K8's. I am also current on our clubs K18 which is very much a tail dragger.
I am also not partuculary light. I have ot lost control but on every K18
launch I need to use nearly full forward stick to prevent over rotation
AFTER lift off at uk rates of acceleration.

Terry Walsh


At 14:53 02 July 2013, Bill D wrote:
Thanks, Andreas. I hope the Brits are reading it.


On Monday, July 1, 2013 6:33:02 PM UTC-6, Andreas Maurer wrote:
Hi Nigel,



On Mon, 01 Jul 2013 14:58:00 +0000, Nigel Pocock

wrote:



If Bill D could be bothered to read my posting before spouting a reply
he

wouls see that I had started the launch with full forward stick in
both

cases.



Really bad mistake. Will make you want to change your pants after you

trtied this in a glider with full-flying elevator. NO glider will take

off with the stick full nose-down if the CG is halfways right.



Hard acceration with these gliders can cause the tail to hit the
ground

hard - not safe.



Safe. Happens all the time, this is what the glider is designed for.





To avoid this the tail of the K8s are usually held down

for the launch. Too hard acceration can cause the glider to shoot into
the

air and immediately into a 45 degree climb despite the stick position.



Absolutely not.



If

the rope breaks at this point you have too little height to recover.
Hence

the winch driver will give slower initial acceleration with these
types.

By regained control I mean the elevator having any effect. Until then
you

are just a passenger.



Absolutely not.







Really sorry to contradict, but the dangers you are describing are

simply not true (or, rather, caused by bad training).





Even if the tail hits the ground more or less hard (which is easy to

avoid by applying power smoothly), the glider takes off at a speed

where elevator control is always perfectly sufficient to control the

pitch up momentum. If the wing flies fast enough to lift the glider,

the elevator flies fast enough to prevent pitch up - if the elevator

is kept in the correct position.



In case you did not know this: Elevator size of at least any German

designed glider is certified (and verified) that there is always 100%

elevator authority to prevent pitch up.



If the acceleration pushes back the hand that is holding the stick

(or, by using a soft cushion, the whole pilot moves backwards), things

look differerent...





In my club we've been doing winch launches for the last 60 years now,

with about 200.000 winch launches. ***Not one single accident*** due

to the causes you describe. Hundreds of pilots,hundreds of student

pilots, hundreds of winch drivers, dozens of instructors, half a dozen

of different winches from an 120 hp V8 engines to 280 hp turbo

Diesel. Gliders range from Spatz, Ka-6, Ka-8, to ASH-25.



Not one single accident.



And no, we do not push the tails of our Ka-8s down.

I've seen morre winch launches that I care to count where the gound

run was less than 6 ft. (ft - not yards!). Naught to 40 mph in less

than a second.





*Any* too-steep winch launch that I ever saw during the last 30 years

was caused by nose-up elevator at the moment of lift off. Any.









I was always taught with ground launch to keep it straight and level
until

the glider lifts off in a shallow climb. When a safe speed had been
reached

to rotate steadily into a full climb. At any point in this process you
can

still recover and land safely using the correct procedures - as taught
be

both the german and british systems.



The German system teaches to keep the stick in the recommended

(trimmed) position. If done halfways properly, any glider will launch

itself and rotate into the climb smoothly ***without any elevator

input***.

Works like a charm for absolutely any glider, be it an L--Spatz, a

Ka-8 or a heavy ASH-25.



An absolute no-no is launching with full nose-down elevator as you are

doing it. Makes a smooth transition into the climb really hard and

often leads to over-controlling.







Cheers from Germany

Andreas





p.s.

The only case where the elevator is not able to control a nose-up

rotation of the glider is, if a full-flying elevator is pushed fully

forward, therefore stalling the complete horizontal tail.

On Tuesday, July 2, 2013 12:42:58 PM UTC-6, Terry Walsh wrote:
I have in excess of 4000 winch launches in many types of Glider includung

K8's. I am also current on our clubs K18 which is very much a tail dragger.

I am also not partuculary light. I have ot lost control but on every K18

launch I need to use nearly full forward stick to prevent over rotation

AFTER lift off at uk rates of acceleration.



Terry Walsh





At 14:53 02 July 2013, Bill D wrote:

Thanks, Andreas. I hope the Brits are reading it.





On Monday, July 1, 2013 6:33:02 PM UTC-6, Andreas Maurer wrote:

Hi Nigel,







On Mon, 01 Jul 2013 14:58:00 +0000, Nigel Pocock



wrote:







If Bill D could be bothered to read my posting before spouting a reply

he



wouls see that I had started the launch with full forward stick in

both



cases.







Really bad mistake. Will make you want to change your pants after you



trtied this in a glider with full-flying elevator. NO glider will take



off with the stick full nose-down if the CG is halfways right.







Hard acceration with these gliders can cause the tail to hit the

ground



hard - not safe.







Safe. Happens all the time, this is what the glider is designed for.











To avoid this the tail of the K8s are usually held down



for the launch. Too hard acceration can cause the glider to shoot into

the



air and immediately into a 45 degree climb despite the stick position.







Absolutely not.







If



the rope breaks at this point you have too little height to recover.

Hence



the winch driver will give slower initial acceleration with these

types.



By regained control I mean the elevator having any effect. Until then

you



are just a passenger.







Absolutely not.















Really sorry to contradict, but the dangers you are describing are



simply not true (or, rather, caused by bad training).











Even if the tail hits the ground more or less hard (which is easy to



avoid by applying power smoothly), the glider takes off at a speed



where elevator control is always perfectly sufficient to control the



pitch up momentum. If the wing flies fast enough to lift the glider,



the elevator flies fast enough to prevent pitch up - if the elevator



is kept in the correct position.







In case you did not know this: Elevator size of at least any German



designed glider is certified (and verified) that there is always 100%



elevator authority to prevent pitch up.







If the acceleration pushes back the hand that is holding the stick



(or, by using a soft cushion, the whole pilot moves backwards), things



look differerent...











In my club we've been doing winch launches for the last 60 years now,



with about 200.000 winch launches. ***Not one single accident*** due



to the causes you describe. Hundreds of pilots,hundreds of student



pilots, hundreds of winch drivers, dozens of instructors, half a dozen



of different winches from an 120 hp V8 engines to 280 hp turbo



Diesel. Gliders range from Spatz, Ka-6, Ka-8, to ASH-25.







Not one single accident.







And no, we do not push the tails of our Ka-8s down.



I've seen morre winch launches that I care to count where the gound



run was less than 6 ft. (ft - not yards!). Naught to 40 mph in less



than a second.











*Any* too-steep winch launch that I ever saw during the last 30 years



was caused by nose-up elevator at the moment of lift off. Any.



















I was always taught with ground launch to keep it straight and level

until



the glider lifts off in a shallow climb. When a safe speed had been

reached



to rotate steadily into a full climb. At any point in this process you

can



still recover and land safely using the correct procedures - as taught

be



both the german and british systems.







The German system teaches to keep the stick in the recommended



(trimmed) position. If done halfways properly, any glider will launch



itself and rotate into the climb smoothly ***without any elevator



input***.



Works like a charm for absolutely any glider, be it an L--Spatz, a



Ka-8 or a heavy ASH-25.







An absolute no-no is launching with full nose-down elevator as you are



doing it. Makes a smooth transition into the climb really hard and



often leads to over-controlling.















Cheers from Germany



Andreas











p.s.



The only case where the elevator is not able to control a nose-up



rotation of the glider is, if a full-flying elevator is pushed fully



forward, therefore stalling the complete horizontal tail.





Why do these stories come exclusively from the UK? No one else seems to have the problem. Maybe the laws of aerodynamics and physics work differently there.

Hi Andreas

200,000 winch launches without a single incident? Not one cable break,
dropped wing, weak link overload? I would be amazed if this were so.

If you have managed that many launches, with the wide variety of
equipment, and never damaged a glider, that is impressive and laudable.

I have to take issue with you - though it is only a personal opinion.

Glider hitting the tail on the ground on launch - you say no problem
ever. Well anecdotal evidence does not prove a theory. So let me
introduce a "Black Swan" for you. I have repaired a Zugfogel 3 that
returned from a nice cross country, with the rudder base split from end
to end. Pilot was warned that his tail had hit the runway on a snatched
launch, he was confident that it was no problem as it had never caused
damage before, and the strike was "not that hard". He got lucky, there
was still a couple of centimetres of fabric holding it together by the
time he landed.

From an engineering point of view I doubt you would find any designer
who would agree that his glider's tail was designed to strike the runway
firmly hundreds of times. Maybe all German runways are soft deep grass,
but I doubt it.

I am not sure on your assertion that all German designed gliders are
designed to have full elevator authority at all design airspeeds. There
is a fair body of research on kiting on aerotow (at much greater speeds
than initial launch) and I recall it included a wide range of various
manufacturers aircraft. The same happens on winch.

So - if the acceleration is such that the couple caused by the vertical
distance between the hook and the CG exceeds the available controlling
couple that the elevator can generate, the aircraft will rotate
uncontrollably. That is why many gliders drop their tail on the take off
run. If you say you have gliders banging the tail down on launch then
you are saying that you are exceeding the controllable range of the
aircraft.

From a weight and balance point of view - light pilots tend to have
more problem that heavy - if the CG is aft the tendency to over rotate
is greater. From a physics point of view high wing + upright pilot tends
to have a higher rotational couple for any given longitudinal
acceleration.

If the acceleration through this uncontrollable part of the regime
happens entirely on the ground, then the glider reaches sufficient speed
for elevator authority with the ground contact preventing undesirable
rotation. If the launch is (a little slower) close to the limit as the
glider leaves the ground, the reduction in drag as the wheel and cable
lift, can give the little extra acceleration. Then the glider is
climbing strongly, and the tail is rotating downward as the pilot moves
the stick forward. If the tail hits the runway you have stressed the
airframe, and possibly damaged the rudder. If the rate of climb is high
enough that the tail misses the runway, you are at a very high angle of
climb, at relatively low speed at very low height. If your equipment is
less than perfect and something goes wrong the consequences get a lot
more serious if you have too low energy.

Do agree on two points:

You should not have the stick in an extreme position during the launch.

All flying tails will easily stall - when elevators are at big
deflections and low airspeed (as will some other pre JAR22 gliders).
Then some time later when the AoA changes and the control un-stalls you
will get a big unexpected force.
Recipe for trouble. Again, anecdotes do not prove the physics, but I
have watched a light pilot in a Std Cirrus do this and overfly the cable
chute in the ensuing back release. Interestingly he was adamant that
this was the right way to do things despite evidence that it was not the
safest approach.

Perhaps we have to agree to disagree. One thing I am certain of though,
the process and experience has to be predictable and consistent. There
are enough other variables involved.
We prefer a controlled three second acceleration to maximum launch
speed. That gives a reasonably controlled 2s ground run and much lower
initial acceleration - and the correctly trimmed glider does as it is
designed to do, and flies off without pilot input.


--
Bruce Greeff
T59D #1771

Hi Bruce,

I think we agree nearly 100%.
You describe the physics just as I would do, however, I'd like to add
a couple of comments.


On Tue, 02 Jul 2013 20:25:03 +0200, BruceGreeff
wrote:

Hi Andreas

200,000 winch launches without a single incident? Not one cable break,
dropped wing, weak link overload? I would be amazed if this were so.

200.000 launches without any uncontrolled pitch up caused by
insufficient elevator authority.

Of course plenty of the typical winch-launch incidents, fortunately no
bad crashes so far.


Glider hitting the tail on the ground on launch - you say no problem
ever. Well anecdotal evidence does not prove a theory. So let me
introduce a "Black Swan" for you.

Well... oldtimers are a different case, aren't they?

From an engineering point of view I doubt you would find any designer
who would agree that his glider's tail was designed to strike the runway
firmly hundreds of times. Maybe all German runways are soft deep grass,
but I doubt it.

I think that grass runways are an important factor here - I'd estimate
that 99.999 of the winch launches in Germany take place on grass
runways. I doubt that anyone who ever heard a Ka-8 tail crash onto a
concrete runway would not try to find a way to prevent that.

Anyway, winch drivers try to provide soft acceleration (we are using
the same standard 3 second 0.5g acceleration as you do), but from time
to time a catapult launch simply happens.

The tail always drops to the ground during initial acceleration, but
in nearly all cases this is relatively soft - definiteloy softer than
any landing.

I am not sure on your assertion that all German designed gliders are
designed to have full elevator authority at all design airspeeds. There
is a fair body of research on kiting on aerotow (at much greater speeds
than initial launch) and I recall it included a wide range of various
manufacturers aircraft. The same happens on winch.

They really are. Do the maths - even the extremely small tails of
an ASW-27 have plenty of lift to control any pitch-up momentum caused
by the tow rope. At least if the correct weak-link is used.
If the latter is (as it seems to become en vogue these days) much
stronger than certified, the bets are off.

Kiting on aerotow is an entirely different matter.
The problem there was not the inability to get the nose of the glider
down, the problem was the very quick climb that followed a nose-up
input on the stick.
If the pilot reacts halfways quickly, he is always able to arrest the
kiting (as proven by thousands of successful aerotows in belly-hook
only Ka-6s each year).

So - if the acceleration is such that the couple caused by the vertical
distance between the hook and the CG exceeds the available controlling
couple that the elevator can generate, the aircraft will rotate
uncontrollably. That is why many gliders drop their tail on the take off
run.

I disagree.
They all drop the tail, don't they?

As long as the glider is slower than liftoff speed, there is of course
insufficient aorodynamic force on the elevator, and of course the
glider drops its tail if there's a halfways decent acceleration. At
liftoff speed it would easily be possible to push the tail up with
forward stick.

I don't think I have ever seen a winch launch in person where the tail
was not on the ground.



If the acceleration through this uncontrollable part of the regime
happens entirely on the ground, then the glider reaches sufficient speed
for elevator authority with the ground contact preventing undesirable
rotation.

Indeed. This is what ahppens 100% of the time in my opinion.
And once airborne, it is the elevator authority that prevents pitch
up.



If the launch is (a little slower) close to the limit as the
glider leaves the ground, the reduction in drag as the wheel and cable
lift, can give the little extra acceleration. Then the glider is
climbing strongly, and the tail is rotating downward as the pilot moves
the stick forward.

Sorry, I cannot imagine the situation you are describing.

What I have seen is this:
- Airspeed too slow
- Winch driver gets notified and immediately increases power
- Increasing winch power causes nose-up rotation
- Pilot's reaction is too slow and too late
- So when he finally reacts, he has to arrest the nose-up rotation
first before he can lower his nose
- Things get interesting


If the tail hits the runway you have stressed the
airframe, and possibly damaged the rudder.

I dare to state that a proper held-off landing with the tail first
generates much greater forces in most cases.

How are you teaching the winch launch?
Here in Germany it is taught that the correct lift off occurs with
main wheel and tail at the same time.

All flying tails will easily stall - when elevators are at big
deflections and low airspeed (as will some other pre JAR22 gliders).

I think these flying tails (early LS-1's and Cirrus are typical
candidates) are the root of most myths of "uncontrolled pitch up
despite stick fully forward".

Perhaps we have to agree to disagree. One thing I am certain of though,
the process and experience has to be predictable and consistent. There
are enough other variables involved.

I absolutely agree.
But I honestly think that winch launching is not as difficult or
angerous as many people try to make it.


We prefer a controlled three second acceleration to maximum launch
speed. That gives a reasonably controlled 2s ground run and much lower
initial acceleration - and the correctly trimmed glider does as it is
designed to do, and flies off without pilot input.

This is exactly the same way we are doing things.


Cheers
Andreas

On Tuesday, July 2, 2013 11:25:03 AM UTC-7, BruceGreeff wrote:

From an engineering point of view I doubt you would find any designer
who would agree that his glider's tail was designed to strike the runway
firmly hundreds of times. Maybe all German runways are soft deep grass,
but I doubt it.

Bruce, what are we wagering here again?

Thanks, Bob K.
http://www.hpaircraft.com/hp-24

On Saturday, June 29, 2013 8:22:46 AM UTC-6, Nigel Pocock wrote:
Excessive initial ecceleration can cause problems with certain types. I

have experienced it with 2 types.

PW5 with stick fully forward at the start of the launch. Hard acceleration

caused the glider to rotate from the nose wheel to the tail wheel and

rocket into the air. I only managed to regain control at about 50ft.

The other one is the K8. Light glider, high wing. Similar problem.



If slow acceleration is a safety problem what about the ground run and take

off with aerotow using belly hooks, and autotows?

Here's a PW-5 winch launch done right. Note the 1 second ground roll.
http://www.youtube.com/watch?v=IseFvZXK7Dw

Here's a K8 also with a one second ground roll.
http://www.youtube.com/watch?v=ict8W0Q5ZpA

Both of these launches were at accelerations greater than 1G. Neither showed an "uncommanded" pitch up. So, neither the gliders nor the acceleration are a problem.