Do your straps up tightly for winch launches!

The UK Air Accident Investigation Branch (AAIB) has
recently published a report on a fatal accident involving
a DG600 sailplane back in 2005.

The circumstances were that the DG600 took a winch
launch, and rotated into an unusually steep climb after
lift off. This was enough to slow down a slightly underpowered
winch to the extent that the glider stalled and flicked
into a spin. The pilot was killed in the ensuing crash.

The experienced pilot was the owner of the DG600 and
maintained it himself as a BGA inspector. It was assessed
from the wreckage that the glider was correctly rigged
and that all the controls were properly connected.
The only anomaly found was that the ASI static was
connected to the Total Energy probe, which might have
caused the ASI to misread. However tests showed that
this would only cause minor errors.

The shoulder straps were found to be somewhat loose
although, as the glider crashed inverted, this may
have been as a result of the crash. It was concluded
that the most likely cause of this accident was that
the pilot had not sufficiently tightened his shoulder
straps and had slid backwards up the seat, which caused
him to inadvertently pull back on the stick in the
process.

I should point out that I had a somewhat similar experience
when I took my first winch launch in a DG101 sailplane,
and was only just about able to retain control with
my fingertips at full stretch. My feet where well off
the rudder pedals! DG single seaters have a very reclined
seat position and the shoulder straps seem to be mounted
a bit too far up.

Can I recommend most strongly that you do your straps
up really tightly and set the rudder pedals at least
a couple of notches nearer for a winch launch, especially
if the sailplane has a well reclined seat. Also only
use very firm seat cushions if these are required.

Derek Copeland

Good advice Derek!

And if your seat back has adjustable 'arms', consider how those arms
will react under increased load and/or bumps, and take appropriate
steps to lock them in properly, or add support. Especially if you use a
more 'forward' position for the seat back.

Bob

Derek Copeland wrote:
The UK Air Accident Investigation Branch (AAIB) has
recently published a report on a fatal accident involving
a DG600 sailplane back in 2005.

The circumstances were that the DG600 took a winch
launch, and rotated into an unusually steep climb after
lift off. This was enough to slow down a slightly underpowered
winch to the extent that the glider stalled and flicked
into a spin. The pilot was killed in the ensuing crash.

The experienced pilot was the owner of the DG600 and
maintained it himself as a BGA inspector. It was assessed
from the wreckage that the glider was correctly rigged
and that all the controls were properly connected.
The only anomaly found was that the ASI static was
connected to the Total Energy probe, which might have
caused the ASI to misread. However tests showed that
this would only cause minor errors.

The shoulder straps were found to be somewhat loose
although, as the glider crashed inverted, this may
have been as a result of the crash. It was concluded
that the most likely cause of this accident was that
the pilot had not sufficiently tightened his shoulder
straps and had slid backwards up the seat, which caused
him to inadvertently pull back on the stick in the
process.

I should point out that I had a somewhat similar experience
when I took my first winch launch in a DG101 sailplane,
and was only just about able to retain control with
my fingertips at full stretch. My feet where well off
the rudder pedals! DG single seaters have a very reclined
seat position and the shoulder straps seem to be mounted
a bit too far up.

Can I recommend most strongly that you do your straps
up really tightly and set the rudder pedals at least
a couple of notches nearer for a winch launch, especially
if the sailplane has a well reclined seat. Also only
use very firm seat cushions if these are required.

Derek Copeland

At 17:00 16 October 2006, Derek Copeland wrote:
The only anomaly found was that the ASI static was
connected to the Total Energy probe, which might have
caused the ASI to misread. However tests showed that
this would only cause minor errors.

How was this conclusion reached? I wouldn't call doubling
the ASI reading a minor error. Or did you mean that
the ASI was connected to a Prandtl tube static instead
of fuselage static?

Derek Copeland wrote:
The UK Air Accident Investigation Branch (AAIB) has
recently published a report on a fatal accident involving
a DG600 sailplane back in 2005.
snip
The only anomaly found was that the ASI static was
connected to the Total Energy probe, which might have
caused the ASI to misread. However tests showed that
this would only cause minor errors.

This seems completely wrong to me. The TE probe should produce a
pressure below static equal to the dynamic pressure, so the
differential pressure to the ASI would be doubled, and the ASI would
read high by 70%. I would not consider this a minor error!

I would seriously question the test results, and the report's
conclusions based on this.

"Derek Copeland" wrote in
message ...
The UK Air Accident Investigation Branch (AAIB) has
recently published a report on a fatal accident involving
a DG600 sailplane back in 2005.
snip
Can I recommend most strongly that you do your straps
up really tightly and set the rudder pedals at least
a couple of notches nearer for a winch launch, especially
if the sailplane has a well reclined seat. Also only
use very firm seat cushions if these are required.


I've had a similar "feet off the pedals experience" in a Std Cirrus when I
visited another club with a high power winch. My club, at that time, was
using reverse pulley auto tow so I'd never experienced a high acceleration
winch launch. I'm fortunate that I'm 6'3" so didn't slide too far back
before my head hit the canopy frame. I was thus able to keep my hand on the
stick.

The problem in that glider, and I suspect others, is that the shoulder
straps don't stop you sliding backwards regardless of how tight they are.
Unless the straps are attached to a point below your shoulders they can't
stop you. The other problem in the Std Cirrus is the lack of upholstery on
the seat pan, making it easy to slide on. My solution was to sit on a thin
rubber mat which stopped all movement.

Stephen

The ASI should be connected to a fuselage static, but
in the case of the accident glider it was connected
to some sort of double pronged European Total energy
(TE) probe in parallel with the varios.

T.E. probes produce a small amount of negative pressure
which increases with airspeed and thereby compensates
the vario for the height gains or losses associated
with speed changes. i.e converts it from a Vertical
Speed Indicator to a soaring Vario.

An ASI works by comparing pitot pressure with static
pressure, so reducing the static pressure will as you
say increase the ASI reading. However the glider had
been flown in this configuration for some time, so
the pilot would have been used to any errors produced.
The AAIB actually set up a rig with the same configuration
and found that the errors where quite small. Presumably
the high pressure generated by the pitot was much greater
than the low pressure generated by the TE probe.

If you want to be really pedantic, the shoulder straps
were actually found to be undone and too long after
the accident, but they may have slipped and then released
during the crash. There is however at least a possibility
that the pilot may have failed to secure the shoulder
straps before taking the launch.

As I have also slipped back in the cockpit of a DG
glider when I didn't quite tighten the shoulder straps
enough for a winch launch, this seems the most reasonable
explanation for this accident to me, and doesn't change
the basic recommendations.

Derek Copeland


At 11:06 17 October 2006, Doug Haluza wrote:

Derek Copeland wrote:
The UK Air Accident Investigation Branch (AAIB) has
recently published a report on a fatal accident involving
a DG600 sailplane back in 2005.

The only anomaly found was that the ASI static was
connected to the Total Energy probe, which might have
caused the ASI to misread. However tests showed that
this would only cause minor errors.

This seems completely wrong to me. The TE probe should
produce a
pressure below static equal to the dynamic pressure,
so the
differential pressure to the ASI would be doubled,
and the ASI would
read high by 70%. I would not consider this a minor
error!

I would seriously question the test results, and the
report's
conclusions based on this.

Derek Copeland wrote:
snip
T.E. probes produce a small amount of negative pressure
which increases with airspeed

Actually an ideal TE probe creates a "negative" differential pressure
exactly equal to the positive differential pressure of the pitot tube
(relative to static). If the ASI was connected to Pitot and TE (instead
of static) then the ASI would read 70% high, because dynamic pressure
is related to airspeed squarred.

An ASI works by comparing pitot pressure with static
pressure, so reducing the static pressure will as you
say increase the ASI reading. However the glider had
been flown in this configuration for some time, so
the pilot would have been used to any errors produced.

No way he compensated for a 70% high reading.

The AAIB actually set up a rig with the same configuration
and found that the errors where quite small. Presumably
the high pressure generated by the pitot was much greater
than the low pressure generated by the TE probe.

This is not correct. Either the explanation is wrong or there was a
problem with the test.

At 11:06 17 October 2006, Doug Haluza wrote:

Derek Copeland wrote:
The UK Air Accident Investigation Branch (AAIB) has
recently published a report on a fatal accident involving
a DG600 sailplane back in 2005.

The only anomaly found was that the ASI static was
connected to the Total Energy probe, which might have
caused the ASI to misread. However tests showed that
this would only cause minor errors.

This seems completely wrong to me. The TE probe should
produce a
pressure below static equal to the dynamic pressure,
so the
differential pressure to the ASI would be doubled,
and the ASI would
read high by 70%. I would not consider this a minor
error!

I would seriously question the test results, and the
report's
conclusions based on this.

Wouldn't the exact effect depend on the relative areas
of the pot pitot and the usually very small holes in
the T.E. probe? The AAIB are normally very thorough
in their investigations, so I am happy to believe them,
and that this error was not the primary cause of the
accident. Neither am I recommending that you should
connect your instruments up in this way.

Derek Copeland

At 01:54 18 October 2006, Doug Haluza wrote:

Derek Copeland wrote:

T.E. probes produce a small amount of negative pressure
which increases with airspeed

Actually an ideal TE probe creates a 'negative' differential
pressure
exactly equal to the positive differential pressure
of the pitot tube
(relative to static). If the ASI was connected to Pitot
and TE (instead
of static) then the ASI would read 70% high, because
dynamic pressure
is related to airspeed squarred.

An ASI works by comparing pitot pressure with static
pressure, so reducing the static pressure will as
you
say increase the ASI reading. However the glider had
been flown in this configuration for some time, so
the pilot would have been used to any errors produced.

No way he compensated for a 70% high reading.

The AAIB actually set up a rig with the same configuration
and found that the errors where quite small. Presumably
the high pressure generated by the pitot was much
greater
than the low pressure generated by the TE probe.

This is not correct. Either the explanation is wrong
or there was a
problem with the test.

At 11:06 17 October 2006, Doug Haluza wrote:

Derek Copeland wrote:
The UK Air Accident Investigation Branch (AAIB) has
recently published a report on a fatal accident involving
a DG600 sailplane back in 2005.

The only anomaly found was that the ASI static was
connected to the Total Energy probe, which might
have
caused the ASI to misread. However tests showed that
this would only cause minor errors.

This seems completely wrong to me. The TE probe should
produce a
pressure below static equal to the dynamic pressure,
so the
differential pressure to the ASI would be doubled,
and the ASI would
read high by 70%. I would not consider this a minor
error!

I would seriously question the test results, and the
report's
conclusions based on this.

Derek Copeland wrote:
Wouldn't the exact effect depend on the relative areas
of the pot pitot and the usually very small holes in
the T.E. probe? The AAIB are normally very thorough
in their investigations, so I am happy to believe them,
and that this error was not the primary cause of the
accident. Neither am I recommending that you should
connect your instruments up in this way.

No, the area of the openings would not matter, unless there was a
significant leak.

If your description is correct, then I would not assume that the
primary cause was the straps, which as you point out could not be
conclusively determined due to post impact damage. Can you check the
report again and make sure you have correctly reported the results?

Doug,

the reading of an ASI is very rarely connected to winch launch accidents,
and certainly not in the initial climb.
Sliding back in the seat (or movement of a seatpan) during initial rotation
has already claimed a number of lives.

Bert

"Doug Haluza" wrote in message
oups.com...

Derek Copeland wrote:
Wouldn't the exact effect depend on the relative areas
of the pot pitot and the usually very small holes in
the T.E. probe? The AAIB are normally very thorough
in their investigations, so I am happy to believe them,
and that this error was not the primary cause of the
accident. Neither am I recommending that you should
connect your instruments up in this way.

No, the area of the openings would not matter, unless there was a
significant leak.

If your description is correct, then I would not assume that the
primary cause was the straps, which as you point out could not be
conclusively determined due to post impact damage. Can you check the
report again and make sure you have correctly reported the results?