Use of weak links

[Paul[_7_]]

Currently the club that I am part of don't seem to be too concerned about
the safety aspects of using the correct weak links for winch launching
and I'd like to know how safe it is.

Currently I see two issues with the winch launching:

1. Sometimes a weak link is not used at all. The gliders are attached
directly to the winch cable (via drogue chute and various connectors).

2. When a weak link is included in the cable (only a primary link - no
reserve link) it is used for all glider types (G102 Astir, G103 Twin II,
ASW20, LS4) and I'm not even sure what the breaking strain is. My guess
is it's a Tost #1 black (1000 daN) weak link but that's hard to tell
because its weathered and the protective sleeve obscures the Tost number.
The weak link is never changed between glider types.

According to what I have read (glider manuals and Tost manual) the
maximum winch load that should be exerted on most of the single seaters
is 500 daN and on the G103 Twin II it's 750 daN.

Am I being paranoid about safety? Are weak links not that important for
safe winch launching?

I took the matter up with the safety officer who said I need to take it
up with the CFI but I'd like to get some advice and input before I engage
with the CFI over the matter.
I'm new to soaring so I don't know it all.

Thanks

[GM]

On Jun 2, 4:43*am, Paul > wrote:
> Currently the club that I am part of don't seem to be too concerned about
> the safety aspects of using the correct weak links for winch launching
> and I'd like to know how safe it is.
>
> Currently I see two issues with the winch launching:
>
> 1. Sometimes a weak link is not used at all. The gliders are attached
> directly to the winch cable (via drogue chute and various connectors).
>
> 2. When a weak link is included in the cable (only a primary link - no
> reserve link) it is used for all glider types (G102 Astir, G103 Twin II,
> ASW20, LS4) and I'm not even sure what the breaking strain is. My guess
> is it's a Tost #1 black (1000 daN) weak link but that's hard to tell
> because its weathered and the protective sleeve obscures the Tost number.
> The weak link is never changed between glider types.
>
> According to what I have read (glider manuals and Tost manual) the
> maximum winch load that should be exerted on most of the single seaters
> is 500 daN and on the G103 Twin II it's 750 daN.
>
> Am I being paranoid about safety? Are weak links not that important for
> safe winch launching?
>
> I took the matter up with the safety officer who said I need to take it
> up with the CFI but I'd like to get some advice and input before I engage
> with the CFI over the matter.
> I'm new to soaring so I don't know it all.
>
> Thanks

Paul,
I am horrified to read this kind of message!! The weaklinks are an
essential safety device to avoid overstressing the glider. Please go
to http://www.tost.de/evers/edefault.htm and research the proper set-
up of the winch launch tackle.
There is a very active discussion group on the internet (winchdesign
on yahoo) trying to revive winch launching in the US in a safe way.
Any accident due to ignorance will give the insurance companies more
reason to choke off these effort! Contact me via PM off-line if you
need more info.
Uli Neumann

[Cats]

On Jun 2, 9:43*am, Paul > wrote:
> Currently the club that I am part of don't seem to be too concerned about
> the safety aspects of using the correct weak links for winch launching
> and I'd like to know how safe it is.
>
> Currently I see two issues with the winch launching:
>
> 1. Sometimes a weak link is not used at all. The gliders are attached
> directly to the winch cable (via drogue chute and various connectors).
>
> 2. When a weak link is included in the cable (only a primary link - no
> reserve link) it is used for all glider types (G102 Astir, G103 Twin II,
> ASW20, LS4) and I'm not even sure what the breaking strain is. My guess
> is it's a Tost #1 black (1000 daN) weak link but that's hard to tell
> because its weathered and the protective sleeve obscures the Tost number.
> The weak link is never changed between glider types.
>
> According to what I have read (glider manuals and Tost manual) the
> maximum winch load that should be exerted on most of the single seaters
> is 500 daN and on the G103 Twin II it's 750 daN.
>
> Am I being paranoid about safety? Are weak links not that important for
> safe winch launching?
>
> I took the matter up with the safety officer who said I need to take it
> up with the CFI but I'd like to get some advice and input before I engage
> with the CFI over the matter.
> I'm new to soaring so I don't know it all.
>
> Thanks

Scary. I fly in the UK, we always use a weak link, what strength to
use is stated by the BGA:
http://www.gliding.co.uk/bgainfo/technical/datasheets/weaklinks.pdf

As it shows, the black weak link is OK for the glass two-seaters but
not the single-seaters. (sorry it includes some Skylaunch stuff as
well)

Also:
http://www.gliding.co.uk/bgainfo/safety/safewinchlaunching.htm

BTW we never use a backup weak link - if you rig it so it doesn't take
a shock load when the main one fails then it will be taking strain
itself and so makes the weak link too strong, if you rig it so it's
not taking any strain then the shock load is likely to make it fail as
well.

[T8]

On Jun 2, 4:43*am, Paul > wrote:
> Currently the club that I am part of don't seem to be too concerned about
> the safety aspects of using the correct weak links for winch launching
> and I'd like to know how safe it is.
>
> Currently I see two issues with the winch launching:
>
> 1. Sometimes a weak link is not used at all. The gliders are attached
> directly to the winch cable (via drogue chute and various connectors).
>
> 2. When a weak link is included in the cable (only a primary link - no
> reserve link) it is used for all glider types (G102 Astir, G103 Twin II,
> ASW20, LS4) and I'm not even sure what the breaking strain is. My guess
> is it's a Tost #1 black (1000 daN) weak link but that's hard to tell
> because its weathered and the protective sleeve obscures the Tost number.
> The weak link is never changed between glider types.
>
> According to what I have read (glider manuals and Tost manual) the
> maximum winch load that should be exerted on most of the single seaters
> is 500 daN and on the G103 Twin II it's 750 daN.
>
> Am I being paranoid about safety? Are weak links not that important for
> safe winch launching?
>
> I took the matter up with the safety officer who said I need to take it
> up with the CFI but I'd like to get some advice and input before I engage
> with the CFI over the matter.
> I'm new to soaring so I don't know it all.
>
> Thanks

Here's hoping that the signal to noise ratio of a one on one
conversation with your CFI is better than that on r.a.s. (see
concurrent thread on altimeter settings, for example :-)).

Yours is a reasonable question that deserves a reasonable response.
My $0.02: you are not being 'paranoid' about anything.

-Evan Ludeman / T8

[Paul[_7_]]

On Wed, 02 Jun 2010 04:28:31 -0700, T8 wrote:
> Here's hoping that the signal to noise ratio of a one on one
> conversation with your CFI is better than that on r.a.s. (see concurrent
> thread on altimeter settings, for example :-)).
>
> Yours is a reasonable question that deserves a reasonable response. My
> $0.02: you are not being 'paranoid' about anything.
>
> -Evan Ludeman / T8


Thanks for the input everyone.

I'll take the matter up with my CFI and if not successful will stick to
aerotows while the rest of the club can risk their lives using the winch.

[Tim Mara]

unbelievable! especially since a weak link is such an easy thing to add,
especially for ground launching!
you might be quite amazed at the numbers of pilots who call me asking what
the "proper weak link" should be when it is such a fundamental question and
one that every prospective student pilot needs to know even before taking a
practical test for a private pilot certificate!

using the TOST weak links is easy and the reserve weak link makes a lot of
sense since ALL weak links fatigue in time and become weaker before actually
breaking.the idea of the reserve weak link is so that when this happened and
the main weak link fails from fatigue the reserve link will hold under
normal loads and the launch is still completed without an actual failure but
the broke link is then visible for the next launch (we check these before
each launch .right? ((you are supposed to) and you know then to replace the
broken link before continuing with another launch. simple to use, and even
simpler to change from one weak link strength to another as needed by using
the notch connectors or similar attachment.you can see more on my website
page http://wingsandwheels.com/page30.htm

regards
Tim Mara

Please visit the Wings & Wheels website at www.wingsandwheels.com


"T8" > wrote in message
...
On Jun 2, 4:43 am, Paul > wrote:
> Currently the club that I am part of don't seem to be too concerned about
> the safety aspects of using the correct weak links for winch launching
> and I'd like to know how safe it is.
>
> Currently I see two issues with the winch launching:
>
> 1. Sometimes a weak link is not used at all. The gliders are attached
> directly to the winch cable (via drogue chute and various connectors).
>
> 2. When a weak link is included in the cable (only a primary link - no
> reserve link) it is used for all glider types (G102 Astir, G103 Twin II,
> ASW20, LS4) and I'm not even sure what the breaking strain is. My guess
> is it's a Tost #1 black (1000 daN) weak link but that's hard to tell
> because its weathered and the protective sleeve obscures the Tost number.
> The weak link is never changed between glider types.
>
> According to what I have read (glider manuals and Tost manual) the
> maximum winch load that should be exerted on most of the single seaters
> is 500 daN and on the G103 Twin II it's 750 daN.
>
> Am I being paranoid about safety? Are weak links not that important for
> safe winch launching?
>
> I took the matter up with the safety officer who said I need to take it
> up with the CFI but I'd like to get some advice and input before I engage
> with the CFI over the matter.
> I'm new to soaring so I don't know it all.
>
> Thanks

Here's hoping that the signal to noise ratio of a one on one
conversation with your CFI is better than that on r.a.s. (see
concurrent thread on altimeter settings, for example :-)).

Yours is a reasonable question that deserves a reasonable response.
My $0.02: you are not being 'paranoid' about anything.

-Evan Ludeman / T8

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[bildan]

On Jun 2, 2:43*am, Paul > wrote:
> Currently the club that I am part of don't seem to be too concerned about
> the safety aspects of using the correct weak links for winch launching
> and I'd like to know how safe it is.
>
> Currently I see two issues with the winch launching:
>
> 1. Sometimes a weak link is not used at all. The gliders are attached
> directly to the winch cable (via drogue chute and various connectors).
>
> 2. When a weak link is included in the cable (only a primary link - no
> reserve link) it is used for all glider types (G102 Astir, G103 Twin II,
> ASW20, LS4) and I'm not even sure what the breaking strain is. My guess
> is it's a Tost #1 black (1000 daN) weak link but that's hard to tell
> because its weathered and the protective sleeve obscures the Tost number.
> The weak link is never changed between glider types.
>
> According to what I have read (glider manuals and Tost manual) the
> maximum winch load that should be exerted on most of the single seaters
> is 500 daN and on the G103 Twin II it's 750 daN.
>
> Am I being paranoid about safety? Are weak links not that important for
> safe winch launching?
>
> I took the matter up with the safety officer who said I need to take it
> up with the CFI but I'd like to get some advice and input before I engage
> with the CFI over the matter.
> I'm new to soaring so I don't know it all.
>
> Thanks

You are not alone. There is a terrible casualness about weak links
out there.

The FAR's are clear. FAR 91.9(a) says if your glider has an Aircraft
Flight Manual which is part of the airworthiness documentation, you
must operate in compliance with that manual. AFM will mandate a
precise (+or- 10%) weak link for both aero tow AND winch launch. As a
practical matter, the best way to comply is to use a steel Tost weak
link. Knots and bits of rope just don't make the grade.

Not using the correct weak link is not only an FAR violation, it
violates common sense. Operators are NOT free to choose their own
weak links.

[Andy[_1_]]

On Jun 2, 1:43*am, Paul > wrote:
> 1. Sometimes a weak link is not used at all. The gliders are attached
> directly to the winch cable (via drogue chute and various connectors).

I can only hope there is some part of the connect system has been
designed to function as the weak link and that you don't understand
how it was designed the work. The alternative is that your club has
decided it's quite ok for the wings to depart the glider during a
launch.

You must understand the cable system and know that it is compatible
with your glider's limitations before you accept a launch. Your
concerns are valid.

Andy

[sisu1a]

> Am I being paranoid about safety? Are weak links not that important for
> safe winch launching?
>
> I took the matter up with the safety officer who said I need to take it
> up with the CFI but I'd like to get some advice and input before I engage
> with the CFI over the matter.
> I'm new to soaring so I don't know it all.
>
> Thanks

Not paranoid, and not only are the weak links CRITICAL for safe winch
launching, so is the rest of the preamble (called a 'strop', or
'trace'), which usually consists of the launch cable terminating with
a stiffened 3-10m section (air compressor hose slipped over rope/cable
is very commonly employed here) after the parachute, with the weaklink
on the winch side of the strop so the pilot to be able to see it (part
of pre-takeoff checklist for winchlaunch= weaklink type/condition...)
from the cockpit. Reason for the stiffened section is to keep it from
being able to snarl up on the landing gear or other non-releasable
bits of glider should the glider get jerked forward slightly before
actually launching.

http://www.tost.de/evers/eprod53/eprod53.htm -weaklinks
http://www.tost.de/evers/eprod54/eprod54.htm -preamble/chutes

There is no need to reinvent the wheel here, so hopefully your club
shapes up on this non-negotiable item so the safety nazis won't need
to descend upon your operation for an intervention since this can
screw us all... seriously.

-Paul (Hanson)

ps. your never 'know it all', but if you stay a perpetual student
you'll prolly get closer than anyone that thinks they do...

pps. If the 'safety officer' deferred this to the CFI, then what's the
point of a safety officer?
makes me think: "safety officer... ur doing it wrong"
http://knowyourmeme.com/photos/26271
http://knowyourmeme.com/photos/6727
http://knowyourmeme.com/photos/6816
http://knowyourmeme.com/photos/1520
http://knowyourmeme.com/photos/1240

[Brian[_1_]]

On Jun 2, 9:31*am, Andy > wrote:
> On Jun 2, 1:43*am, Paul > wrote:
>
> > 1. Sometimes a weak link is not used at all. The gliders are attached
> > directly to the winch cable (via drogue chute and various connectors).
>
> I can only hope there is some part of the connect system has been
> designed to function as the weak link and that you don't understand
> how it was designed the work. *The alternative is that your club has
> decided it's quite ok for the wings to depart the glider during a
> launch.
>
> You must understand the cable system and know that it is compatible
> with your glider's limitations before you accept a launch. *Your
> concerns are valid.
>
> Andy

IMO it is easily a violation of FAR 91.13(a) careless and reckless
operation and if there is ever a launching incident that the FAA
investigates and it is found that NO weak link is being used when one
is required I am sure someone will end up with a suspended license at
best.

I hope Andy is correct and there really is a system in place that you
are just not aware of so discuss it with your CFI.

However it is important to understand that while the weak link is a
critical part of the launch system, it will take more that missing to
have “wings fall off the airplane” The weak link is just a portion of
the complete safety system. And while it may be possible to damage the
structure of the aircraft, mostly likely the Tow hook or related
structure, the wings will stay on the aircraft unless other safety
mechanisms are ignored as well.

Specifically what I am saying is that unless you are exceeding the
Maximum Winch Launch speed of the glider it should be impossible to
overstress the wings as the wing will stall before exceeding maximum
structural load of the aircraft.

Brian

[Brian Whatcott]

Paul wrote:
> Currently the club that I am part of don't seem to be too concerned about
> the safety aspects of using the correct weak links for winch launching
> and I'd like to know how safe it is.
>
> Currently I see two issues with the winch launching:
>
> 1. Sometimes a weak link is not used at all. The gliders are attached
> directly to the winch cable (via drogue chute and various connectors).
>
> 2. When a weak link is included in the cable (only a primary link - no
> reserve link) it is used for all glider types (G102 Astir, G103 Twin II,
> ASW20, LS4) and I'm not even sure what the breaking strain is. My guess
> is it's a Tost #1 black (1000 daN) weak link but that's hard to tell
> because its weathered and the protective sleeve obscures the Tost number.
> The weak link is never changed between glider types.
>
> According to what I have read (glider manuals and Tost manual) the
> maximum winch load that should be exerted on most of the single seaters
> is 500 daN and on the G103 Twin II it's 750 daN.
>
> Am I being paranoid about safety? Are weak links not that important for
> safe winch launching?
>
> I took the matter up with the safety officer who said I need to take it
> up with the CFI but I'd like to get some advice and input before I engage
> with the CFI over the matter.
> I'm new to soaring so I don't know it all.
>
> Thanks

The FARs have a rule for it. If I recall: 80 to 200% of ...(forget which
weight/force...)
Darn it!

Brian W

[[email protected]]

On Jun 2, 8:31*pm, brian whatcott > wrote:
> Paul wrote:
> > Currently the club that I am part of don't seem to be too concerned about
> > the safety aspects of using the correct weak links for winch launching
> > and I'd like to know how safe it is.
>
> > Currently I see two issues with the winch launching:
>
> > 1. Sometimes a weak link is not used at all. The gliders are attached
> > directly to the winch cable (via drogue chute and various connectors).
>
> > 2. When a weak link is included in the cable (only a primary link - no
> > reserve link) it is used for all glider types (G102 Astir, G103 Twin II,
> > ASW20, LS4) and I'm not even sure what the breaking strain is. My guess
> > is it's a Tost #1 black (1000 daN) weak link but that's hard to tell
> > because its weathered and the protective sleeve obscures the Tost number.

[Karen]

> I took the matter up with the safety officer who said I need to take it
> up with the CFI but I'd like to get some advice and input before I engage
> with the CFI over the matter.
> I'm new to soaring so I don't know it all.
>
> Thanks

And exactly why is some CFIG the last word on what is OK or safe?

Winching without a weak link is right up there on the suppidity list
with downwind ground launches or tail-scrapping vaults into the air
instead of gradual rotations. All of which we have observed by so-
called "experienced" CFI's some of whom have turned out to have
relatively little experience or worse have practiced bad habits for
years.

Interesting that a newbe has to come on the field, point out the
emperor has no clothes to the soaring sages and bring it to light on a
dicussion group for common sense and support.

BTW. See the preliminary findings on Sandhill Soaring's winch mishap
that took a life a year ago.

Winch cables can be too strong and break things inside the aircraft,
long before the wings come off; or way too fragile and introduce an
unexpected surprise.

http://www.livingstondaily.com/article/20100602/NEWS01/6020302/Malfunction+blamed+for+fatal+glider+accident

Michael

[bildan]

On Jun 2, 6:31*pm, brian whatcott > wrote:
> Paul wrote:
> > Currently the club that I am part of don't seem to be too concerned about
> > the safety aspects of using the correct weak links for winch launching
> > and I'd like to know how safe it is.
>
> > Currently I see two issues with the winch launching:
>
> > 1. Sometimes a weak link is not used at all. The gliders are attached
> > directly to the winch cable (via drogue chute and various connectors).
>
> > 2. When a weak link is included in the cable (only a primary link - no
> > reserve link) it is used for all glider types (G102 Astir, G103 Twin II,
> > ASW20, LS4) and I'm not even sure what the breaking strain is. My guess
> > is it's a Tost #1 black (1000 daN) weak link but that's hard to tell
> > because its weathered and the protective sleeve obscures the Tost number.

[bildan]

On Jun 2, 2:43*am, Paul > wrote:
> Currently the club that I am part of don't seem to be too concerned about
> the safety aspects of using the correct weak links for winch launching
> and I'd like to know how safe it is.
>
> Currently I see two issues with the winch launching:
>
> 1. Sometimes a weak link is not used at all. The gliders are attached
> directly to the winch cable (via drogue chute and various connectors).
>
> 2. When a weak link is included in the cable (only a primary link - no
> reserve link) it is used for all glider types (G102 Astir, G103 Twin II,
> ASW20, LS4) and I'm not even sure what the breaking strain is. My guess
> is it's a Tost #1 black (1000 daN) weak link but that's hard to tell
> because its weathered and the protective sleeve obscures the Tost number.
> The weak link is never changed between glider types.
>
> According to what I have read (glider manuals and Tost manual) the
> maximum winch load that should be exerted on most of the single seaters
> is 500 daN and on the G103 Twin II it's 750 daN.
>
> Am I being paranoid about safety? Are weak links not that important for
> safe winch launching?
>
> I took the matter up with the safety officer who said I need to take it
> up with the CFI but I'd like to get some advice and input before I engage
> with the CFI over the matter.
> I'm new to soaring so I don't know it all.
>
> Thanks

Paul, that you would question safety procedures in this way suggests
you will have a long and illustrious career as a glider pilot. I only
wish others would do the same.

I propose your club bring in outside experts for a winch clinic.

Bill D

[Tim Mara]

80-200% for aero-towing *
100-200% for ground launching *
of max certificated gross weight *
tim
-
Please visit the Wings & Wheels website at www.wingsandwheels.com



> wrote in message
...
On Jun 2, 8:31 pm, brian whatcott > wrote:
> Paul wrote:
> > Currently the club that I am part of don't seem to be too concerned
> > about
> > the safety aspects of using the correct weak links for winch launching
> > and I'd like to know how safe it is.
>
> > Currently I see two issues with the winch launching:
>
> > 1. Sometimes a weak link is not used at all. The gliders are attached
> > directly to the winch cable (via drogue chute and various connectors).
>
> > 2. When a weak link is included in the cable (only a primary link - no
> > reserve link) it is used for all glider types (G102 Astir, G103 Twin II,
> > ASW20, LS4) and I'm not even sure what the breaking strain is. My guess
> > is it's a Tost #1 black (1000 daN) weak link but that's hard to tell
> > because its weathered and the protective sleeve obscures the Tost
> > number.
> > The weak link is never changed between glider types.
>
> > According to what I have read (glider manuals and Tost manual) the
> > maximum winch load that should be exerted on most of the single seaters
> > is 500 daN and on the G103 Twin II it's 750 daN.
>
> > Am I being paranoid about safety? Are weak links not that important for
> > safe winch launching?
>
> > I took the matter up with the safety officer who said I need to take it
> > up with the CFI but I'd like to get some advice and input before I
> > engage
> > with the CFI over the matter.
> > I'm new to soaring so I don't know it all.
>
> > Thanks
>
> The FARs have a rule for it. If I recall: 80 to 200% of ...(forget which
> weight/force...)
> Darn it!
>
> Brian W- Hide quoted text -
>
> - Show quoted text -

Check what that applies to. I predict you will see it relates to aero
towing.
UH

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[Brian Whatcott]

Brian wrote:
/snip/
> Specifically what I am saying is that unless you are exceeding the
> Maximum Winch Launch speed of the glider it should be impossible to
> overstress the wings as the wing will stall before exceeding maximum
> structural load of the aircraft.
>
> Brian
>

This is a perfectly sound argument in many phases of flight.
But a tow capable of exerting enough force on a stalled structure
will certainly break it. A winch need not relax when a wing stalls....
Visualize an airframe being hauled along at an AoA of 90 degrees,
to exaggerate this point...

Brian W

[Andreas Maurer]

On Thu, 03 Jun 2010 19:43:46 -0500, brian whatcott
> wrote:


>> Specifically what I am saying is that unless you are exceeding the
>> Maximum Winch Launch speed of the glider it should be impossible to
>> overstress the wings as the wing will stall before exceeding maximum
>> structural load of the aircraft.
>>
>> Brian
>>
>
>This is a perfectly sound argument in many phases of flight.
> But a tow capable of exerting enough force on a stalled structure
>will certainly break it. A winch need not relax when a wing stalls....
>Visualize an airframe being hauled along at an AoA of 90 degrees,
>to exaggerate this point...

This won't break the wing spars either.

As long as the IAS is below VA (in other words: in the green range of
the airspeed indicator), no control input at all can damage the glider
- the definition of VA is that this is the speed under which a high
speed stall will prevent exceeding the maximum g-load. So, as long as
you are slower than VA, you are safe.

(Of course - combined control inputs can indeed break the structure
even below VA, usually by torsional load on the tail boom by a
deflected rudder at speeds close to VA combined with significant yaw
angle.)


The problem of exceeding the Maximum Winch Launch speed is not the
wing, but the attachment of the tow hook to the fuselage structure.
Pretty hard to explain why you landed with the belly hook missing...


Cheers
Andreas
Bye
Andreas

[Andreas Maurer]

On Thu, 3 Jun 2010 14:38:51 -0400, "Tim Mara" >
wrote:

>80-200% for aero-towing *
>100-200% for ground launching *
>of max certificated gross weight *

Most amazing.
This violates the POHs of all the gliders I know.

Cheers
Andreas

Bye
Andreas

[Chris Nicholas[_2_]]

For clarity, did the original poster mean Chief Flying Instructor by
"CFI" (UK and some other countries' usage), or "some CFIG” as another
(USA?) poster thought?

Either way, what is the safety officer doing, not caring and deferring
to the the CFI whoever it is?

Chris N.

[Darryl Ramm]

On Jun 4, 10:15*am, Chris Nicholas > wrote:
> For clarity, did the original poster mean Chief Flying Instructor by
> "CFI" (UK and some other countries' usage), *or "some CFIG” as another
> (USA?) poster thought?
>
> Either way, what is the safety officer doing, not caring and deferring
> to the the CFI whoever it is?
>
> Chris N.

The original message was from South Africa. Presumably the OP meant
Chief Flying Instructor.

Darryl

[Andy[_1_]]

On Jun 4, 6:27*am, Andreas Maurer > wrote:

>As long as the IAS is below VA (in other words: in the green range of
>the airspeed indicator), no control input at all can damage the glider

Are you sure about that? It was my understanding the Va is never
marked in the ASI and that the top of the green arc is the maximum
operating speed in rough air. Va may be lower than that.

Andy

[Tony[_5_]]

On Jun 4, 1:53*pm, Andy > wrote:
> On Jun 4, 6:27*am, Andreas Maurer > wrote:
>
> >As long as the IAS is below VA (in other words: in the green range of
> >the airspeed indicator), no control input at all can damage the glider
>
> Are you sure about that? *It was my understanding the Va is never
> marked in the ASI and that the top of the green arc is the maximum
> operating speed in rough air. Va may be lower than that.
>
> Andy

andy - that is correct

[Brian[_1_]]

On Jun 3, 6:43*pm, brian whatcott > wrote:
> Brian wrote:
>
> /snip/
>
> > Specifically what I am saying is that unless you are exceeding the
> > Maximum Winch Launch speed of the glider it should be impossible to
> > overstress the wings as the wing will stall before exceeding maximum
> > structural load of the aircraft.
>
> > Brian
>
> This is a perfectly sound argument in many phases of flight.
> * But a *tow capable of exerting enough force on a stalled structure
> will certainly break it. A winch need not relax when a wing stalls....
> Visualize an airframe being hauled along at an AoA of 90 degrees,
> to exaggerate this point...
>
> Brian W

While technically correct, in practice it probably isn't much of a
factor.
For my 750lb glider with a 120sq.ft. of wing rated for 6g's and as 1g
stall speed of 40 mph the 6g stall speed is 97mph.
For the flat plate drag of the wing area to exceed 6g's on the wing a
120mph is required by my calculation, which means the winch operator
is going to have be pulling me at 120mph since I am stalled and no
longer have any angular acceleration.

A 200% weak link should break at 69mph if I understand it correctly
(3G load) Interestingly IIRC my max ground launch speed is 69mph.

Brian C.

[Mike Schumann]

On 6/2/2010 7:23 AM, Paul wrote:
> On Wed, 02 Jun 2010 04:28:31 -0700, T8 wrote:
>> Here's hoping that the signal to noise ratio of a one on one
>> conversation with your CFI is better than that on r.a.s. (see concurrent
>> thread on altimeter settings, for example :-)).
>>
>> Yours is a reasonable question that deserves a reasonable response. My
>> $0.02: you are not being 'paranoid' about anything.
>>
>> -Evan Ludeman / T8
>
>
> Thanks for the input everyone.
>
> I'll take the matter up with my CFI and if not successful will stick to
> aerotows while the rest of the club can risk their lives using the winch.

Weak links are there to protect the structural integrity of the glider.
If your club is not using weak links, they may be damaging the glider,
which might not be obvious. You are still putting yourself at risk if
you are flying a club glider that may have been damaged, regardless of
whether you are winch launching or using aero tows.

--
Mike Schumann

[Brian Whatcott]

Andreas Maurer wrote:
> On Thu, 03 Jun 2010 19:43:46 -0500, brian whatcott
> > wrote:
>
>
>>> Specifically what I am saying is that unless you are exceeding the
>>> Maximum Winch Launch speed of the glider it should be impossible to
>>> overstress the wings as the wing will stall before exceeding maximum
>>> structural load of the aircraft.
>>>
>>> Brian
>>>
>> This is a perfectly sound argument in many phases of flight.
>> But a tow capable of exerting enough force on a stalled structure
>> will certainly break it. A winch need not relax when a wing stalls....
>> Visualize an airframe being hauled along at an AoA of 90 degrees,
>> to exaggerate this point...
>
> This won't break the wing spars either.
>
> As long as the IAS is below VA (in other words: in the green range of
> the airspeed indicator), no control input at all can damage the glider
> - the definition of VA is that this is the speed under which a high
> speed stall will prevent exceeding the maximum g-load. So, as long as
> you are slower than VA, you are safe.
>
> (Of course - combined control inputs can indeed break the structure
> even below VA, usually by torsional load on the tail boom by a
> deflected rudder at speeds close to VA combined with significant yaw
> angle.)
>
>
> The problem of exceeding the Maximum Winch Launch speed is not the
> wing, but the attachment of the tow hook to the fuselage structure.
> Pretty hard to explain why you landed with the belly hook missing...
>
>
> Cheers
> Andreas
> Bye
> Andreas

Better to think twice and write once.

For instance, how does your ASI indicate at 90 deg AoA ?
If an airframe is designed for 1.5 (the design factor)
times limit load (often 4 g)
then if it is pulled with a force exceeding this, at high AoA,
wing breakage is guaranteed.

Sincerely

Brian W

[Brian Whatcott]

Andreas Maurer wrote:
> On Thu, 3 Jun 2010 14:38:51 -0400, "Tim Mara" >
> wrote:
>
>> 80-200% for aero-towing *
>> 100-200% for ground launching *
>> of max certificated gross weight *
>
> Most amazing.
> This violates the POHs of all the gliders I know.
>
> Cheers
> Andreas
>
> Bye
> Andreas

There you go again, Andreas :-)
The thread indicated that the regs specify:
poh, or if not specified, the other.

Better to think twice and write once

Brian W

[Brian Whatcott]

Brian wrote:
> On Jun 3, 6:43 pm, brian whatcott > wrote:
>> Brian wrote:
>>
>> /snip/
>>
>>> Specifically what I am saying is that unless you are exceeding the
>>> Maximum Winch Launch speed of the glider it should be impossible to
>>> overstress the wings as the wing will stall before exceeding maximum
>>> structural load of the aircraft.
>>> Brian
>> This is a perfectly sound argument in many phases of flight.
>> But a tow capable of exerting enough force on a stalled structure
>> will certainly break it. A winch need not relax when a wing stalls....
>> Visualize an airframe being hauled along at an AoA of 90 degrees,
>> to exaggerate this point...
>>
>> Brian W
>
> While technically correct, in practice it probably isn't much of a
> factor.
> For my 750lb glider with a 120sq.ft. of wing rated for 6g's and as 1g
> stall speed of 40 mph the 6g stall speed is 97mph.
> For the flat plate drag of the wing area to exceed 6g's on the wing a
> 120mph is required by my calculation, which means the winch operator
> is going to have be pulling me at 120mph since I am stalled and no
> longer have any angular acceleration.
>
> A 200% weak link should break at 69mph if I understand it correctly
> (3G load) Interestingly IIRC my max ground launch speed is 69mph.
>
> Brian C.
>
>
There is plenty I don't know about gliders. That you believe a glider is
designed for 6g limit loads for example. I thought the load limit was
lower, on condition parachutes are worn?
But then, there's plenty I don't know about sailplane design...

Brian W

[Andy[_1_]]

On Jun 4, 6:54*pm, brian whatcott > wrote:
> I thought the load limit was
> lower, on condition parachutes are worn?

Do any sailplanes require a parachute to be worn as a condition of
operation. I don't know of any. Schleicher required equipment for
my glider is a parachute or a cushion of a specified thickness.

Andy

[bildan]

On Jun 4, 7:41*pm, brian whatcott > wrote:
> Andreas Maurer wrote:
> > On Thu, 03 Jun 2010 19:43:46 -0500, brian whatcott
> > > wrote:
>
> >>> Specifically what I am saying is that unless you are exceeding the
> >>> Maximum Winch Launch speed of the glider it should be impossible to
> >>> overstress the wings as the wing will stall before exceeding maximum
> >>> structural load of the aircraft.
>
> >>> Brian
>
> >> This is a perfectly sound argument in many phases of flight.
> >> *But a *tow capable of exerting enough force on a stalled structure
> >> will certainly break it. A winch need not relax when a wing stalls....
> >> Visualize an airframe being hauled along at an AoA of 90 degrees,
> >> to exaggerate this point...
>
> > This won't break the wing spars either.
>
> > As long as the IAS is below VA (in other words: in the green range of
> > the airspeed indicator), no control input at all can damage the glider
> > - the definition of VA is that this is the speed under which a high
> > speed stall will prevent exceeding the maximum g-load. So, as long as
> > you are slower than VA, you are safe.
>
> > (Of course - combined control inputs can indeed break the structure
> > even below VA, usually by torsional load on the tail boom by a
> > deflected rudder at speeds close to VA combined with significant yaw
> > angle.)
>
> > The problem of exceeding the Maximum Winch Launch speed is not the
> > wing, but the attachment of the tow hook to the fuselage structure.
> > Pretty hard to explain why you landed with the belly hook missing...
>
> > Cheers
> > Andreas
> > Bye
> > Andreas
>
> Better to think twice and write once.
>
> For instance, how does your ASI indicate at 90 deg AoA ?
> If an airframe is designed for 1.5 (the design factor)
> * times limit load (often 4 g)
> then if it is pulled with a force exceeding this, at high AoA,
> * wing breakage is guaranteed.
>
> Sincerely
>
> Brian W

Back to the OP question.

It's absolute insanity to winch launch a glider with anything but the
exact weak link demanded by the POH. There's simply no wiggle room -
you have to do what the manual says. However, with that link, there's
zero risk of overloading the wing structure. (If the POH doesn't
specify a winch weak link, I wouldn't winch launch the glider.)

While you're at it, buy a "preamble" from W&W (Tost) or Klaus Fey's
(www.eqip.de) and don't try to cobble up one with rope, hardware store
carabiners and a surplus 'chute. There's some real safety issues with
how these things are put together you don't want to learn the hard way.

[Brian Whatcott]

brian whatcott wrote:
>/snip/
> For instance, how does your ASI indicate at 90 deg AoA ?
> If an airframe is designed for 1.5 (the design factor)
> times limit load (often 4 g)
> then if it is pulled with a force exceeding this, at high AoA,
> wing breakage is guaranteed.
>
> Sincerely
>
> Brian W

I received a private note that mentioned that gliders may well
be built to 6+g limit loads and that parachutes are not
mandatory - with some notable exceptions.
Where DO I get my preconceptions? :-)

Brian W

[Brian Whatcott]

Andy wrote:
> On Jun 4, 6:54 pm, brian whatcott > wrote:
>> I thought the load limit was
>> lower, on condition parachutes are worn?
>
> Do any sailplanes require a parachute to be worn as a condition of
> operation. I don't know of any. Schleicher required equipment for
> my glider is a parachute or a cushion of a specified thickness.
>
> Andy

I was way off base, by all accounts. I hear they can be required for
competition or aerobatics...

Brian W

[jcarlyle]

I understand completely the need for a weak link when ground launching
- it's there to protect the glider's structural integrity. The need
for a weak link for aerotow was less obvious to me. Searching the web
it became clear that an aerotow weak link is there to try to protect
the tow pilot. In case a glider "kites", the tow pilot has a much
better chance of survival if the tow rope breaks, as there's a history
of the tow plane's release not working in this case.

Despite this laudable purpose, I've never seen an aerotow weak link
used in my (admittedly limited) experience at some 10 airports in the
US. Maybe I've missed the weak links - are they attached at the tow
plane's tow hook? I think, though, most US glider operators use tow
rope with a breaking strength of 80 to 200% of max certified operating
weight of the glider, instead of a weak leak.

Just out of curiousity (really not trying to start something), are
there US gliderports that use aerotow weak links?

-John

[Frank Whiteley]

On Jun 5, 3:09*pm, jcarlyle > wrote:
> I understand completely the need for a weak link when ground launching
> - it's there to protect the glider's structural integrity. The need
> for a weak link for aerotow was less obvious to me. Searching the web
> it became clear that an aerotow weak link is there to try to protect
> the tow pilot. In case a glider "kites", the tow pilot has a much
> better chance of survival if the tow rope breaks, as there's a history
> of the tow plane's release not working in this case.
>
> Despite this laudable purpose, I've never seen an aerotow weak link
> used in my (admittedly limited) experience at some 10 airports in the
> US. Maybe I've missed the weak links - are they attached at the tow
> plane's tow hook? I think, though, most US glider operators use tow
> rope with a breaking strength of 80 to 200% of max certified operating
> weight of the glider, instead of a weak leak.
>
> Just out of curiousity (really not trying to start something), are
> there US gliderports that use aerotow weak links?
>
> -John

Yes.

[Andreas Maurer]

On Fri, 04 Jun 2010 20:41:48 -0500, brian whatcott
> wrote:


>For instance, how does your ASI indicate at 90 deg AoA ?
>If an airframe is designed for 1.5 (the design factor)
> times limit load (often 4 g)
>then if it is pulled with a force exceeding this, at high AoA,
> wing breakage is guaranteed.


Sorry Brian,

I have to admit I don't understand what you mean.
What do you want to say with that 90 deg AoA?


My point was that a force exceeding the design load is simply not
possible below VA, no matter how high AoA is.

[Andreas Maurer]

On Fri, 4 Jun 2010 11:53:04 -0700 (PDT), Andy >
wrote:

>On Jun 4, 6:27*am, Andreas Maurer > wrote:
>
>>As long as the IAS is below VA (in other words: in the green range of
>>the airspeed indicator), no control input at all can damage the glider
>
>Are you sure about that? It was my understanding the Va is never
>marked in the ASI and that the top of the green arc is the maximum
>operating speed in rough air. Va may be lower than that.

You are absolutely correct - the maximum operating speed in rough air
might be different from Va.


But:
Usually (at least in German gliders) only Va is marked on the ASI (top
of the green arc).

Example ASK-21:
Va 180 kp/h (top of green arc)
Maximum operating speed in rough air 200 kp/h (not marked in ASI).

It might well be possible that it's different for other gliders, but
so far I cannot remember haviong flown one.

[Brian Whatcott]

Andreas Maurer wrote:

> I have to admit I don't understand what you mean.
> What do you want to say with that 90 deg AoA?

That AoA makes your IAS observation rather difficult?
:-)

Brian W

[Brian[_1_]]

On Jun 5, 6:22*pm, Andreas Maurer > wrote:
> On Fri, 04 Jun 2010 20:41:48 -0500, brian whatcott

> Sorry Brian,
>
> I have to admit I don't understand what you mean.
> What do you want to say with that 90 deg AoA?
>
> My point was that a force exceeding the design load is simply not
> possible below VA, no matter how high AoA is.

Andreas,

What Brian W,was trying to say is that it is possible to overload the
wing by simply by the flat plate drag on the wing when it is attached
to the winch. Think of the plane just falling with no horizontal speed
(90deg Angle of Attack). With it not attached to the winch it would
reach a terminal velocity and limit the amount of load that is applied
to the wings. With it attached to the winch it could exceed it's
terminal velocity and apply additional load to the wings, perhaps
enough to fail the structure.

My gut feeling is that it would take quite a bit of vertical velocity
to fail the wing, but I tried applying my admittedly limited math
skills to it and came up with about 120mph to apply 6g's load to
fairly typical single place glider. This was a lower velocity than I
expected but still pretty unreasonable to think it is possible in that
it would mean that the winch operator is pulling the cable in at
120mph.

Brian C.

[Andreas Maurer]

On Sun, 6 Jun 2010 07:21:57 -0700 (PDT), Brian >
wrote:

>What Brian W,was trying to say is that it is possible to overload the
>wing by simply by the flat plate drag on the wing when it is attached
>to the winch. Think of the plane just falling with no horizontal speed
>(90deg Angle of Attack). With it not attached to the winch it would
>reach a terminal velocity and limit the amount of load that is applied
>to the wings. With it attached to the winch it could exceed it's
>terminal velocity and apply additional load to the wings, perhaps
>enough to fail the structure.

Ahhh.... I start to see the light.
A 90 degree AoA is, of course, a situation that can happen easily if
the pilot makes the slightest mistake.... lol.



>My gut feeling is that it would take quite a bit of vertical velocity
>to fail the wing, but I tried applying my admittedly limited math
>skills to it and came up with about 120mph to apply 6g's load to
>fairly typical single place glider. This was a lower velocity than I
>expected but still pretty unreasonable to think it is possible in that
>it would mean that the winch operator is pulling the cable in at
>120mph.

If you are attached to a winch cable at an AoA of 90 degrees, being
pulled towards the winch with 120 mph, I am pretty sure that a broken
wing spar is one of your minor problems.

[Scott Lamont]

Isn't the CG hook going to back release long before 90 degree AoA
anyway? It will release based on the angle between the wire and the
glider not the AoA...maybe 60 degrees AoA?

Scott

[bildan]

On Jun 6, 2:19*pm, Scott Lamont > wrote:
> Isn't the CG hook going to back release long before 90 degree AoA
> anyway? It will release based on the angle between the wire and the
> glider not the AoA...maybe 60 degrees AoA?
>
> Scott

70 degrees is typical.

[Andreas Maurer]

On Sun, 6 Jun 2010 13:19:11 -0700 (PDT), Scott Lamont
> wrote:

>Isn't the CG hook going to back release long before 90 degree AoA
>anyway? It will release based on the angle between the wire and the
>glider not the AoA...maybe 60 degrees AoA?

Sure - you are correct.

But you are not going to reach 90 degrees AoA anyway - I haven't
measured what AoA is possible in a glider if ypou pul back fully, but
I doubt that it's more than 30 degrees.

[Brian[_1_]]

>
> If you are attached to a winch cable at an AoA of 90 degrees, being
> pulled towards the winch with 120 mph, I am pretty sure that a broken
> wing spar is one of your minor problems.

True the 90deg AOA was justa theoritical way to look at the loads on
a stalled wing.

The point is that to have a wing separate you are going to have to
have defeated at least two safety features such as the weak link and
exceeding the maximum winch launch speed.

Brian

[John Smith]

Brian wrote:
> True the 90deg AOA was justa theoritical way to look at the loads on
> a stalled wing.

As soon as the wing stalls, the load decreases.

[Brian Whatcott]

John Smith wrote:
> Brian wrote:
>> True the 90deg AOA was justa theoritical way to look at the loads on
>> a stalled wing.
>
> As soon as the wing stalls, the load decreases.

Oh, really?

Brian W

[Brian[_1_]]

On Jun 6, 5:54*pm, John Smith > wrote:
> Brian wrote:
> > True the 90deg AOA *was justa theoritical way to look at the loads on
> > a stalled wing.
>
> As soon as the wing stalls, the load decreases.

Yes it decreases, but there is some load on it still. Even a stalled
wings produces some lift just not nearly as much as a flying wing.

Brian C.

[ZZ]

Paul
I am a CFIG and I know very little about winch launching
gliders...never done it. What I do know is how difficult it is for a
newbie to challenge their CFI or their captain or in general, challenge
authority over aviation saftey issues.

I applaud you sir for doing so.

Another Paul
ZZ







On 6/2/2010 1:43 AM, Paul wrote:
> Currently the club that I am part of don't seem to be too concerned about
> the safety aspects of using the correct weak links for winch launching
> and I'd like to know how safe it is.
>
> Currently I see two issues with the winch launching:
>
> 1. Sometimes a weak link is not used at all. The gliders are attached
> directly to the winch cable (via drogue chute and various connectors).
>
> 2. When a weak link is included in the cable (only a primary link - no
> reserve link) it is used for all glider types (G102 Astir, G103 Twin II,
> ASW20, LS4) and I'm not even sure what the breaking strain is. My guess
> is it's a Tost #1 black (1000 daN) weak link but that's hard to tell
> because its weathered and the protective sleeve obscures the Tost number.
> The weak link is never changed between glider types.
>
> According to what I have read (glider manuals and Tost manual) the
> maximum winch load that should be exerted on most of the single seaters
> is 500 daN and on the G103 Twin II it's 750 daN.
>
> Am I being paranoid about safety? Are weak links not that important for
> safe winch launching?
>
> I took the matter up with the safety officer who said I need to take it
> up with the CFI but I'd like to get some advice and input before I engage
> with the CFI over the matter.
> I'm new to soaring so I don't know it all.
>
> Thanks

[Brian Whatcott]

Brian wrote:
> On Jun 6, 5:54 pm, John Smith > wrote:
>> Brian wrote:
>>> True the 90deg AOA was justa theoritical way to look at the loads on
>>> a stalled wing.
>> As soon as the wing stalls, the load decreases.
>
> Yes it decreases, but there is some load on it still. Even a stalled
> wings produces some lift just not nearly as much as a flying wing.
>
> Brian C.

How about drag?

B

[Andreas Maurer]

On Mon, 07 Jun 2010 05:20:48 -0500, brian whatcott
> wrote:

>Brian wrote:
>> On Jun 6, 5:54 pm, John Smith > wrote:
>>> Brian wrote:
>>>> True the 90deg AOA was justa theoritical way to look at the loads on
>>>> a stalled wing.
>>> As soon as the wing stalls, the load decreases.
>>
>> Yes it decreases, but there is some load on it still. Even a stalled
>> wings produces some lift just not nearly as much as a flying wing.
>>
>> Brian C.
>
>How about drag?

Forget the drag - you cannot go fast enough with 90 degrees AoA to
produce any significant amount of drag.

Even if you did - the horizontal tail would make sure that your nose
is going to be pointed forward again.

Your 90 degrees AoA is not ging to happen in real life.


Cheers
Andreas

Bye
Andreas

[John Smith]

Andreas Maurer wrote:
> Forget the drag - you cannot go fast enough with 90 degrees AoA to
> produce any significant amount of drag.

I'd rather say that with a 90° AoA you have *only* drag.

[Martin Gregorie[_5_]]

On Mon, 07 Jun 2010 13:54:50 +0200, Andreas Maurer wrote:

> On Mon, 07 Jun 2010 05:20:48 -0500, brian whatcott
> > wrote:
>
>>Brian wrote:
>>> On Jun 6, 5:54 pm, John Smith > wrote:
>>>> Brian wrote:
>>>>> True the 90deg AOA was justa theoritical way to look at the loads
>>>>> on a stalled wing.
>>>> As soon as the wing stalls, the load decreases.
>>>
>>> Yes it decreases, but there is some load on it still. Even a stalled
>>> wings produces some lift just not nearly as much as a flying wing.
>>>
>>> Brian C.
>>
>>How about drag?
>
> Forget the drag - you cannot go fast enough with 90 degrees AoA to
> produce any significant amount of drag.
>
There's another point that hasn't been mentioned - many winches can't
pull in cable at anything like Vwinch for most gliders, e.g. most single
seaters have a Vwinch of 65kts or higher but I'm told our Supacat's
maximum cable speed is 55 kts.

This doesn't mean that it can't break gliders: try this thought
experiment. Launch without a weak link, wait until the glider is at 60-70
degrees from the winch and ramp the winch up to full power to cause a
gross overspeed. This is the situation that will put maximum load on the
wings and it is the situation where the weak link is designed to fail.

At least one of these things is very likely to happen:
(1) the pilot pulls the bung
(2) a back release, if the glider gets far enough overhead of the winch
(3) the hook gets pulled out of the glider
(4) the wings break
(5) the cable snaps

arranged in increasing severity and (my guess) decreasing probability
since I think that one of the less severe events will happen before the
more severe ones.

Some time back during a rainstorm our then CFI gave a talk about how the
various airframe limits are set. I remember him saying that Vwinch is 95%
of the speed at which the wing's maximum design loading is reached when
the glider is overhead the winch with the stick fully back.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[Cats]

On Jun 7, 3:41*pm, Martin Gregorie >
wrote:
> On Mon, 07 Jun 2010 13:54:50 +0200, Andreas Maurer wrote:
> > On Mon, 07 Jun 2010 05:20:48 -0500, brian whatcott
> > > wrote:
>
> >>Brian wrote:
> >>> On Jun 6, 5:54 pm, John Smith > wrote:
> >>>> Brian wrote:
> >>>>> True the 90deg AOA *was justa theoritical way to look at the loads
> >>>>> on a stalled wing.
> >>>> As soon as the wing stalls, the load decreases.
>
> >>> Yes it decreases, but there is some load on it still. Even a stalled
> >>> wings produces some lift just not nearly as much as a flying wing.
>
> >>> Brian C.
>
> >>How about drag?
>
> > Forget the drag - you cannot go fast enough with 90 degrees AoA to
> > produce any significant amount of drag.
>
> There's another point that hasn't been mentioned - many winches can't
> pull in cable at anything like Vwinch for most gliders, e.g. most single
> seaters have a Vwinch of 65kts or higher but I'm told our Supacat's
> maximum cable speed is 55 kts.
>
> This doesn't mean that it can't break gliders: try this thought
> experiment. Launch without a weak link, wait until the glider is at 60-70
> degrees from the winch and ramp the winch up to full power to cause a
> gross overspeed. This is the situation that will put maximum load on the
> wings and it is the situation where the weak link is designed to fail.
>
> At least one of these things is very likely to happen:
> (1) the pilot pulls the bung
> (2) a back release, if the glider gets far enough overhead of the winch
> (3) the hook gets pulled out of the glider
> (4) the wings break
> (5) the cable snaps
>
> arranged in increasing severity and (my guess) decreasing probability
> since I think that one of the less severe events will happen before the
> more severe ones.
<snip>

Think I'd place cable snaps at #3, hook gets pulled out at #4 and
wings break at #5 on the grounds that we practise cable breaks, the
hook pulling out shouldn't affect *this* flight and wings breaking
certainly will.

[Martin Gregorie[_5_]]

On Mon, 07 Jun 2010 08:42:16 -0700, Cats wrote:

> On Jun 7, 3:41Â*pm, Martin Gregorie >
> wrote:
>> On Mon, 07 Jun 2010 13:54:50 +0200, Andreas Maurer wrote:
>> > On Mon, 07 Jun 2010 05:20:48 -0500, brian whatcott
>> > > wrote:
>>
>> >>Brian wrote:
>> >>> On Jun 6, 5:54 pm, John Smith > wrote:
>> >>>> Brian wrote:
>> >>>>> True the 90deg AOA Â*was justa theoritical way to look at the
>> >>>>> loads on a stalled wing.
>> >>>> As soon as the wing stalls, the load decreases.
>>
>> >>> Yes it decreases, but there is some load on it still. Even a
>> >>> stalled wings produces some lift just not nearly as much as a
>> >>> flying wing.
>>
>> >>> Brian C.
>>
>> >>How about drag?
>>
>> > Forget the drag - you cannot go fast enough with 90 degrees AoA to
>> > produce any significant amount of drag.
>>
>> There's another point that hasn't been mentioned - many winches can't
>> pull in cable at anything like Vwinch for most gliders, e.g. most
>> single seaters have a Vwinch of 65kts or higher but I'm told our
>> Supacat's maximum cable speed is 55 kts.
>>
>> This doesn't mean that it can't break gliders: try this thought
>> experiment. Launch without a weak link, wait until the glider is at
>> 60-70 degrees from the winch and ramp the winch up to full power to
>> cause a gross overspeed. This is the situation that will put maximum
>> load on the wings and it is the situation where the weak link is
>> designed to fail.
>>
>> At least one of these things is very likely to happen: (1) the pilot
>> pulls the bung
>> (2) a back release, if the glider gets far enough overhead of the winch
>> (3) the hook gets pulled out of the glider
>> (4) the wings break
>> (5) the cable snaps
>>
>> arranged in increasing severity and (my guess) decreasing probability
>> since I think that one of the less severe events will happen before the
>> more severe ones.
> <snip>
>
> Think I'd place cable snaps at #3, hook gets pulled out at #4 and wings
> break at #5 on the grounds that we practise cable breaks, the hook
> pulling out shouldn't affect *this* flight and wings breaking certainly
> will.
>
I was being pessimistic and assuming a new 3/16" steel cable is being
used and made a guestimate that a new cable is stronger than a set of
used glider wings. I'd certainly expect the hook to pull out before the
spars snapped. I've taken my hook out for a thorough clean-up and have a
pretty good idea of what its bolted to!

I'm also assuming that a less severe event occurrence will reduce the
load and prevent the more severe events from happening. e.g. pulling the
hook out will prevent the spar or cable from breaking.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[Derek C]

On Jun 4, 2:27*pm, Andreas Maurer > wrote:
> On Thu, 03 Jun 2010 19:43:46 -0500, brian whatcott
>
> > wrote:
> >> Specifically what I am saying is that unless you are exceeding the
> >> Maximum Winch Launch speed of the glider it should be impossible to
> >> overstress the wings as the wing will stall before exceeding maximum
> >> structural load of the aircraft.
>
> >> Brian
>
> >This is a perfectly sound argument in many phases of flight.
> > *But a *tow capable of exerting enough force on a stalled structure
> >will certainly break it. A winch need not relax when a wing stalls....
> >Visualize an airframe being hauled along at an AoA of 90 degrees,
> >to exaggerate this point...
>
> This won't break the wing spars either.
>
> As long as the IAS is below VA (in other words: in the green range of
> the airspeed indicator), no control input at all can damage the glider
> - the definition of VA is that this is the speed under which a high
> speed stall will prevent exceeding the maximum g-load. So, as long as
> you are slower than VA, you are safe.
>
> (Of course - combined control inputs can indeed break the structure
> even below VA, usually by torsional load on the tail boom by a
> deflected rudder at speeds close to VA combined with significant yaw
> angle.)
>
> The problem of exceeding the Maximum Winch Launch speed is not the
> wing, but the attachment of the tow hook to the fuselage structure.
> Pretty hard to explain why you landed with the belly hook missing...
>
> Cheers
> Andreas
> Bye
> Andreas

Hi Andreas,

I thought you would know better that that! Gliders have a lower
maximum winch launching speed than Va called Vw. This is because the
pull is applied as a point load in the centre of the fuselage and,
unlike in the manoeuvring case, there is no g unloading. Essentially
the cable is pulling the fuselage down while the wings are providing
large amounts of upward lift, which puts a large bending moment on the
mainspar. This is fairly obvious if you watch a floppy winged glider
being winch launched, when the wings bend quite alarmingly, especially
near the top of the launch when the forces are most opposed. The
recommended weak link is set by by the designer so that it fails well
before the mainspar does. It is possible that other bits of structure
such as the hook mounting will fail first. The only cases where I have
known this happen were to old wooden gliders where the wood has become
slightly rotten in the hook area.

Essentially the weak link acts as a fuse that breaks before the glider
does. Generally to damage a glider you would have to hit a sharp-edged
gust while pulling back hard against a powerful winch, near the top of
the launch, with an overstrength weak link, and exceeding VW, all at
the same time.

Derek Copeland

[bildan]

> Some time back during a rainstorm our then CFI gave a talk about how the
> various airframe limits are set. I remember him saying that Vwinch is 95%
> of the speed at which the wing's maximum design loading is reached when
> the glider is overhead the winch with the stick fully back.
>
> --
> martin@ * | Martin Gregorie
> gregorie. | Essex, UK
> org * * * |

Your CFI may have said that but there's no engineering data or
certification specifications to back it up.

There's no chance of overstressing an airworthy glider on a winch
launch when using the correct weak link.

[Martin Gregorie[_5_]]

On Mon, 07 Jun 2010 12:21:31 -0700, bildan wrote:

>> Some time back during a rainstorm our then CFI gave a talk about how
>> the various airframe limits are set. I remember him saying that Vwinch
>> is 95% of the speed at which the wing's maximum design loading is
>> reached when the glider is overhead the winch with the stick fully
>> back.
>>
>> --
>> martin@ Â* | Martin Gregorie
>> gregorie. | Essex, UK
>> org Â* Â* Â* |
>
> Your CFI may have said that but there's no engineering data or
> certification specifications to back it up.
>
He was talking us through JAR 22 at the time and JAR 22.583 looks pretty
prescriptive to me.

> There's no chance of overstressing an airworthy glider on a winch launch
> when using the correct weak link.
>
Maybe so but note that JAR 22.583 defines the max weak link strength as
the *lesser* of 83% of structural damage limit or max achievable lift
with full up elevator and JAR 22.585 says the hook must withstand the
larger of 125% of the weak link breaking load and the glider's MTOW.

I agree that 22.583 and 22.585 taken together guarantee no damage if the
right weak link is used, but I'd remind you that this discussion was
triggered by a question about a club that was winching with NO weak link.
JAR 22.583 has no guarantee against overstressing the glider under those
conditions because it specifically says that its OK to design a glider
for a weak link that breaks at a lower load than the wing can generate
with full up elevator. Unless there's a clause somewhere else in JAR 22
that would prevent it, this implies that a compliant glider can be broken
by pulling the stick back during an overspeed if it is winched on an
incorrect weak link.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[Brian Whatcott]

John Smith wrote:
> Andreas Maurer wrote:
>> Forget the drag - you cannot go fast enough with 90 degrees AoA to
>> produce any significant amount of drag.
>
> I'd rather say that with a 90° AoA you have *only* drag.

Quite. Cd reaches its peak (around 2) at 90 deg AoA, a notably bell
shaped curve 0 - 180 deg AoA

Cl peaks around 15, drops then rises again to peak around 45 deg AoA
falling to zero round 90 AoA according to some NASA trials of several
representative airfoils.

It was written of several WWI incidents, that a falling leaf full stall
could sometimes be walked away from.
In those machines, going fast was not a prerequisite.

Brian W

[Martin Gregorie[_5_]]

On Mon, 07 Jun 2010 20:55:46 +0000, Martin Gregorie wrote:

> On Mon, 07 Jun 2010 12:21:31 -0700, bildan wrote:
>
>>> Some time back during a rainstorm our then CFI gave a talk about how
>>> the various airframe limits are set. I remember him saying that Vwinch
>>> is 95% of the speed at which the wing's maximum design loading is
>>> reached when the glider is overhead the winch with the stick fully
>>> back.
>>>
>>> --
>>> martin@ Â* | Martin Gregorie
>>> gregorie. | Essex, UK
>>> org Â* Â* Â* |
>>
>> Your CFI may have said that but there's no engineering data or
>> certification specifications to back it up.
>>
> He was talking us through JAR 22 at the time and JAR 22.583 looks pretty
> prescriptive to me.
>
>> There's no chance of overstressing an airworthy glider on a winch
>> launch when using the correct weak link.
>>
> Maybe so but note that JAR 22.583 defines the max weak link strength as
> the *lesser* of 83% of structural damage limit or max achievable lift
> with full up elevator and JAR 22.585 says the hook must withstand the
> larger of 125% of the weak link breaking load and the glider's MTOW.
>
> I agree that 22.583 and 22.585 taken together guarantee no damage if the
> right weak link is used, but I'd remind you that this discussion was
> triggered by a question about a club that was winching with NO weak
> link. JAR 22.583 has no guarantee against overstressing the glider under
> those conditions because it specifically says that its OK to design a
> glider for a weak link that breaks at a lower load than the wing can
> generate with full up elevator. Unless there's a clause somewhere else
> in JAR 22 that would prevent it, this implies that a compliant glider
^^^^^^^^^^^^^^^^^^
> can be broken by pulling the stick back during an overspeed if it is
^^^^^^
> winched on an incorrect weak link.

This should read "it is possible for some compliant gliders to be".


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[Brian Whatcott]

Martin Gregorie wrote:
/snip/
>>
> I was being pessimistic and assuming a new 3/16" steel cable is being
> used and made a guestimate that a new cable is stronger than a set of
> used glider wings. I'd certainly expect the hook to pull out before the
> spars snapped. I've taken my hook out for a thorough clean-up and have a
> pretty good idea of what its bolted to!
>
> I'm also assuming that a less severe event occurrence will reduce the
> load and prevent the more severe events from happening. e.g. pulling the
> hook out will prevent the spar or cable from breaking.
>
>

Strength, according to this supplier:
Long URL:
http://www.ematerialhandling.com/materialhandling/stainless_steel/cable/stainless_steel_cable.htm

TinyURL format:
http://tinyurl.com/6ztmkh

3/16 diam. stainless cable

Construction: 1X19
Material: 304 316
Weight/1000ft 72 lb
wkg load limit 940 lb 854
breaking load 4700 lb 4270

Construction: 7X7
Weight/1000ft 62 lb
wkg 740 670
brk 3700 3350

Construction: 7X19
Wt/1000ft 65 lb
wkg 740 642
brk 3700 3210

(I believe galvanized is usually a little stronger?)

Supposing that sailplanes are designed to meet 6g limit loads,
the most flexible 316 stainless 7X19 cable would break
when transmitting a 6g load to an airframe capable
of reacting over 535 lb at 1g (6 X 535 = 3215 lb)

Brian W

[Grider Pirate]

On Jun 7, 5:32*pm, Martin Gregorie >
wrote:
> On Mon, 07 Jun 2010 20:55:46 +0000, Martin Gregorie wrote:
> > On Mon, 07 Jun 2010 12:21:31 -0700, bildan wrote:
>
> >>> Some time back during a rainstorm our then CFI gave a talk about how
> >>> the various airframe limits are set. I remember him saying that Vwinch
> >>> is 95% of the speed at which the wing's maximum design loading is
> >>> reached when the glider is overhead the winch with the stick fully
> >>> back.
>
> >>> --
> >>> martin@ * | Martin Gregorie
> >>> gregorie. | Essex, UK
> >>> org * * * |
>
> >> Your CFI may have said that but there's no engineering data or
> >> certification specifications to back it up.
>
> > He was talking us through JAR 22 at the time and JAR 22.583 looks pretty
> > prescriptive to me.
>
> >> There's no chance of overstressing an airworthy glider on a winch
> >> launch when using the correct weak link.
>
> > Maybe so but note that JAR 22.583 defines the max weak link strength as
> > the *lesser* of 83% of structural damage limit or max achievable lift
> > with full up elevator and JAR 22.585 says the hook must withstand the
> > larger of 125% of the weak link breaking load and the glider's MTOW.
>
> > I agree that 22.583 and 22.585 taken together guarantee no damage if the
> > right weak link is used, but I'd remind you that this discussion was
> > triggered by a question about a club that was winching with NO weak
> > link. JAR 22.583 has no guarantee against overstressing the glider under
> > those conditions because it specifically says that its OK to design a
> > glider for a weak link that breaks at a lower load than the wing can
> > generate with full up elevator. Unless there's a clause somewhere else
> > in JAR 22 that would prevent it, this implies that a compliant glider
>
> * * * * * * * * * * * * * * * * * * * * * * * * * * *^^^^^^^^^^^^^^^^^^
>
> > can be broken by pulling the stick back during an overspeed if it is
> * ^^^^^^
> > winched on an incorrect weak link.
>
> This should read "it is possible for some compliant gliders to be".
>
> --
> martin@ * | Martin Gregorie
> gregorie. | Essex, UK
> org * * * |- Hide quoted text -
>
> - Show quoted text -

Right, the point, if I'm not mistaken, is to USE A WEAK LINK (of the
correct breaking strength).

[Bruce]

On 2010/06/07 07:00 PM, Martin Gregorie wrote:
> On Mon, 07 Jun 2010 08:42:16 -0700, Cats wrote:
>
>> On Jun 7, 3:41 pm, Martin >
>> wrote:
>>> On Mon, 07 Jun 2010 13:54:50 +0200, Andreas Maurer wrote:
>>>> On Mon, 07 Jun 2010 05:20:48 -0500, brian whatcott
>>>> > wrote:
>>>
>>>>> Brian wrote:
>>>>>> On Jun 6, 5:54 pm, John > wrote:
>>>>>>> Brian wrote:
>>>>>>>> True the 90deg AOA was justa theoritical way to look at the
>>>>>>>> loads on a stalled wing.
>>>>>>> As soon as the wing stalls, the load decreases.
>>>
>>>>>> Yes it decreases, but there is some load on it still. Even a
>>>>>> stalled wings produces some lift just not nearly as much as a
>>>>>> flying wing.
>>>
>>>>>> Brian C.
>>>
>>>>> How about drag?
>>>
>>>> Forget the drag - you cannot go fast enough with 90 degrees AoA to
>>>> produce any significant amount of drag.
>>>
>>> There's another point that hasn't been mentioned - many winches can't
>>> pull in cable at anything like Vwinch for most gliders, e.g. most
>>> single seaters have a Vwinch of 65kts or higher but I'm told our
>>> Supacat's maximum cable speed is 55 kts.
>>>
>>> This doesn't mean that it can't break gliders: try this thought
>>> experiment. Launch without a weak link, wait until the glider is at
>>> 60-70 degrees from the winch and ramp the winch up to full power to
>>> cause a gross overspeed. This is the situation that will put maximum
>>> load on the wings and it is the situation where the weak link is
>>> designed to fail.
>>>
>>> At least one of these things is very likely to happen: (1) the pilot
>>> pulls the bung
>>> (2) a back release, if the glider gets far enough overhead of the winch
>>> (3) the hook gets pulled out of the glider
>>> (4) the wings break
>>> (5) the cable snaps
>>>
>>> arranged in increasing severity and (my guess) decreasing probability
>>> since I think that one of the less severe events will happen before the
>>> more severe ones.
>> <snip>
>>
>> Think I'd place cable snaps at #3, hook gets pulled out at #4 and wings
>> break at #5 on the grounds that we practise cable breaks, the hook
>> pulling out shouldn't affect *this* flight and wings breaking certainly
>> will.
>>
> I was being pessimistic and assuming a new 3/16" steel cable is being
> used and made a guestimate that a new cable is stronger than a set of
> used glider wings. I'd certainly expect the hook to pull out before the
> spars snapped. I've taken my hook out for a thorough clean-up and have a
> pretty good idea of what its bolted to!
>
> I'm also assuming that a less severe event occurrence will reduce the
> load and prevent the more severe events from happening. e.g. pulling the
> hook out will prevent the spar or cable from breaking.
>
>
Interestingly we actually had some engineer members intrigued by this go
and measure the ultimate strength of the winch cable in use.

So - dyneema is another case entirely, and I have no data for
multistrand cable joined with ferrules - but 2 metric ton breaking
strain single strand wire broke reliably at ~900kg at the knot joining
it to the ring on the weak link.

Ergo it is pretty redundant putting a black Tost weak link on.

Not suggesting that no weak link is a good idea, just that the chances
of simple mechanical failure on the cable is higher than you think.
Especially after the wire gets abraded and work hardened.

If you work out the weight of the cable hanging from the hook - it will
seldom exceed 150Kg. Most of the force vector on the hook is from the
winch pulling. In the limiting case this is pulling straight down. At
this point the winch effectively becomes a sling load. I have witnessed
a ham fisted combination of winch driver and Blanik L13 pilot do this.
The vertical component was sufficient to momentarily lift one side of
the winch off the ground. Clear air under the wheel and both jacks.

The Blanik was no doubt way above Vwinch and pulling back heroically to
slow things down.

The resultant massive birdsnest came from the cable failing at the
attachment to the yoke - not from the blue weak link.

--- news://freenews.netfront.net/ - complaints: ---

[Frank Whiteley]

On Jun 7, 6:53*pm, brian whatcott > wrote:
> Martin Gregorie wrote:
>
> /snip/
>
>
>
> > I was being pessimistic and assuming a new 3/16" steel cable is being
> > used and made a guestimate that a new cable is stronger than a set of
> > used glider wings. I'd certainly expect the hook to pull out before the
> > spars snapped. I've taken my hook out for a thorough clean-up and have a
> > pretty good idea of what its bolted to!
>
> > I'm also assuming that a less severe event occurrence will reduce the
> > load and prevent the more severe events from happening. e.g. pulling the
> > hook out will prevent the spar or cable from breaking.
>
> Strength, according to this supplier:
> Long URL:http://www.ematerialhandling.com/materialhandling/stainless_steel/cab...
>
> TinyURL format:http://tinyurl.com/6ztmkh
>
> 3/16 diam. stainless cable
>
> Construction: 1X19
> Material: * * * * * 304 * * * * 316
> Weight/1000ft * * * *72 lb
> wkg load limit * * *940 lb * * *854
> breaking load * * *4700 lb * * 4270
>
> Construction: 7X7
> Weight/1000ft * * * * 62 lb
> wkg * * * * * * * * *740 * * * *670
> brk * * * * * * * * 3700 * * * 3350
>
> Construction: 7X19
> Wt/1000ft * * * * * * 65 lb
> wkg * * * * * * * * *740 * * * *642
> brk * * * * * * * * 3700 * * * 3210
>
> (I believe galvanized is usually a little stronger?)
>
> Supposing that sailplanes are designed to meet 6g limit loads,
> the most flexible 316 stainless 7X19 cable would break
> * when transmitting a 6g load to an airframe capable
> of reacting over 535 lb at 1g * (6 X 535 = 3215 lb)
>
> Brian W

Brian,

1x19 is seldom used, if ever. 7/7 5/32" (4.8lbs/100ft) or
3/16" (6.1lbs/100ft), or metric equivalent, is most commonly used
steel wire rope. Typically the product known as Galvanized Aircraft
Steel Wire Rope. A few places use solid wire. Never heard of
stainless in use, likely due to cost. Tends to be more expensive and
more brittle than the other. Rule of thumb for fatigue reduction is
roller/guide radius 60x the wire diameter. However, the SSA plan
underwriter (last I heard) is not providing liability insurance upon
renewal for use of steel wire rope. Synthetic Dyneema or Spectra
based rope products (or heavier poly ropes in some cases) are the
used. They are as strong or stronger than steel for the same
diameter, easily spiced, have no recoil and less mass so are more
safely handled, and have high UV tolerance. I believe Amsteel Blue
to be the superior product considering strength and longevity. It's
at least 4x the price of steel wire rope.

Rule of thumb, apart from the manufacturers limits, for winch weak
links is 1.3 x AUW. This is close to the charts, see the datasheets
link below.

See
http://www.gliding.co.uk/bgainfo/safety/safewinchlaunching.htm

and the data sheets for glider by make/model

http://www.gliding.co.uk/bgainfo/technical/datasheets.htm

This is UK info, but quite useful.

Frank W

[Frank Whiteley]

On Jun 7, 10:38*pm, Bruce > wrote:
> On 2010/06/07 07:00 PM, Martin Gregorie wrote:
>
> > On Mon, 07 Jun 2010 08:42:16 -0700, Cats wrote:
>
> >> On Jun 7, 3:41 pm, Martin >
> >> wrote:
> >>> On Mon, 07 Jun 2010 13:54:50 +0200, Andreas Maurer wrote:
> >>>> On Mon, 07 Jun 2010 05:20:48 -0500, brian whatcott
> >>>> > *wrote:
>
> >>>>> Brian wrote:
> >>>>>> On Jun 6, 5:54 pm, John > *wrote:
> >>>>>>> Brian wrote:
> >>>>>>>> True the 90deg AOA *was justa theoritical way to look at the
> >>>>>>>> loads on a stalled wing.
> >>>>>>> As soon as the wing stalls, the load decreases.
>
> >>>>>> Yes it decreases, but there is some load on it still. Even a
> >>>>>> stalled wings produces some lift just not nearly as much as a
> >>>>>> flying wing.
>
> >>>>>> Brian C.
>
> >>>>> How about drag?
>
> >>>> Forget the drag - you cannot go fast enough with 90 degrees AoA to
> >>>> produce any significant amount of drag.
>
> >>> There's another point that hasn't been mentioned - many winches can't
> >>> pull in cable at anything like Vwinch for most gliders, e.g. most
> >>> single seaters have a Vwinch of 65kts or higher but I'm told our
> >>> Supacat's maximum cable speed is 55 kts.
>
> >>> This doesn't mean that it can't break gliders: try this thought
> >>> experiment. Launch without a weak link, wait until the glider is at
> >>> 60-70 degrees from the winch and ramp the winch up to full power to
> >>> cause a gross overspeed. This is the situation that will put maximum
> >>> load on the wings and it is the situation where the weak link is
> >>> designed to fail.
>
> >>> At least one of these things is very likely to happen: (1) the pilot
> >>> pulls the bung
> >>> (2) a back release, if the glider gets far enough overhead of the winch
> >>> (3) the hook gets pulled out of the glider
> >>> (4) the wings break
> >>> (5) the cable snaps
>
> >>> arranged in increasing severity and (my guess) decreasing probability
> >>> since I think that one of the less severe events will happen before the
> >>> more severe ones.
> >> <snip>
>
> >> Think I'd place cable snaps at #3, hook gets pulled out at #4 and wings
> >> break at #5 on the grounds that we practise cable breaks, the hook
> >> pulling out shouldn't affect *this* flight and wings breaking certainly
> >> will.
>
> > I was being pessimistic and assuming a new 3/16" steel cable is being
> > used and made a guestimate that a new cable is stronger than a set of
> > used glider wings. I'd certainly expect the hook to pull out before the
> > spars snapped. I've taken my hook out for a thorough clean-up and have a
> > pretty good idea of what its bolted to!
>
> > I'm also assuming that a less severe event occurrence will reduce the
> > load and prevent the more severe events from happening. e.g. pulling the
> > hook out will prevent the spar or cable from breaking.
>
> Interestingly we actually had some engineer members intrigued by this go
> and measure the ultimate strength of the winch cable in use.
>
> So - dyneema is another case entirely, and I have no data for
> multistrand cable joined with ferrules - but 2 metric ton breaking
> strain single strand wire broke reliably at ~900kg at the knot joining
> it to the ring on the weak link.
>
> Ergo it is pretty redundant putting a black Tost weak link on.
>
> Not suggesting that no weak link is a good idea, just that the chances
> of simple mechanical failure on the cable is higher than you think.
> Especially after the wire gets abraded and work hardened.
>
> If you work out the weight of the cable hanging from the hook - it will
> seldom exceed 150Kg. Most of the force vector on the hook is from the
> winch pulling. In the limiting case this is pulling straight down. At
> this point the winch effectively becomes a sling load. I have witnessed
> a ham fisted combination of winch driver and Blanik L13 pilot do this.
> The vertical component was sufficient to momentarily lift one side of
> the winch off the ground. Clear air under the wheel and both jacks.
>
> The Blanik was no doubt way above Vwinch and pulling back heroically to
> slow things down.
>
> The resultant massive birdsnest came from the cable failing at the
> attachment to the yoke - not from the blue weak link.
>
> --- news://freenews.netfront.net/ - complaints: ---

Stainless, copper, and aluminum sleeves can produce 100% strength if
machine swaged and 95% when properly hand swaged. They are swaged in
pairs about 12 inches apart so slippage can be seen visually. I've
had the back end of an XJ-6 Jag lifted off the ground by an L-13 on
auto tow and one side of a winch lifted off the ground by an L-23.
IIRC, red links in use on both.

Frank Whiteley

[Derek C]

On Jun 8, 5:49*am, Frank Whiteley > wrote:
> On Jun 7, 6:53*pm, brian whatcott > wrote:
>
>
>
>
>
> > Martin Gregorie wrote:
>
> > /snip/
>
> > > I was being pessimistic and assuming a new 3/16" steel cable is being
> > > used and made a guestimate that a new cable is stronger than a set of
> > > used glider wings. I'd certainly expect the hook to pull out before the
> > > spars snapped. I've taken my hook out for a thorough clean-up and have a
> > > pretty good idea of what its bolted to!
>
> > > I'm also assuming that a less severe event occurrence will reduce the
> > > load and prevent the more severe events from happening. e.g. pulling the
> > > hook out will prevent the spar or cable from breaking.
>
> > Strength, according to this supplier:
> > Long URL:http://www.ematerialhandling.com/materialhandling/stainless_steel/cab...
>
> > TinyURL format:http://tinyurl.com/6ztmkh
>
> > 3/16 diam. stainless cable
>
> > Construction: 1X19
> > Material: * * * * * 304 * * * * 316
> > Weight/1000ft * * * *72 lb
> > wkg load limit * * *940 lb * * *854
> > breaking load * * *4700 lb * * 4270
>
> > Construction: 7X7
> > Weight/1000ft * * * * 62 lb
> > wkg * * * * * * * * *740 * * * *670
> > brk * * * * * * * * 3700 * * * 3350
>
> > Construction: 7X19
> > Wt/1000ft * * * * * * 65 lb
> > wkg * * * * * * * * *740 * * * *642
> > brk * * * * * * * * 3700 * * * 3210
>
> > (I believe galvanized is usually a little stronger?)
>
> > Supposing that sailplanes are designed to meet 6g limit loads,
> > the most flexible 316 stainless 7X19 cable would break
> > * when transmitting a 6g load to an airframe capable
> > of reacting over 535 lb at 1g * (6 X 535 = 3215 lb)
>
> > Brian W
>
> Brian,
>
> 1x19 is seldom used, if ever. *7/7 5/32" (4.8lbs/100ft) or
> 3/16" (6.1lbs/100ft), or metric equivalent, is most commonly used
> steel wire rope. Typically the product known as Galvanized Aircraft
> Steel Wire Rope. *A few places use solid wire. *Never heard of
> stainless in use, likely due to cost. *Tends to be more expensive and
> more brittle than the other. *Rule of thumb for fatigue reduction is
> roller/guide radius 60x the wire diameter. *However, the SSA plan
> underwriter (last I heard) is not providing liability insurance upon
> renewal for use of steel wire rope. *Synthetic Dyneema or Spectra
> based rope products (or heavier poly ropes in some cases) are the
> used. *They are as strong or stronger than steel for the same
> diameter, easily spiced, have no recoil and less mass so are more
> safely handled, and have high UV tolerance. * I believe Amsteel Blue
> to be the superior product considering strength and longevity. *It's
> at least 4x the price of steel wire rope.
>
> Rule of thumb, apart from the manufacturers limits, for winch weak
> links is 1.3 x AUW. *This is close to the charts, see the datasheets
> link below.
>
> Seehttp://www.gliding.co.uk/bgainfo/safety/safewinchlaunching.htm
>
> and the data sheets for glider by make/model
>
> http://www.gliding.co.uk/bgainfo/technical/datasheets.htm
>
> This is UK info, but quite useful.
>
> Frank W- Hide quoted text -
>
> - Show quoted text -

What's wrong with UK data? We do more than 2/3rd of our glider
launches by winch, so hopefully we know what we are doing by now!

Derek Copeland

[Derek C]

It is better not to use a reserve weak link. This requires a doubled
link which have to be of different designs, The main link has two
round holes and the reserve has one slightly slotted hole. We had a
fatality in the UK where somebody inadvertantly fitted two main links
to the carrier, which effectively doubled the strength of the weak
link, and then a glider had a mainspar failure during the launch on a
rather windy rough day. See:

http://www.aaib.gov.uk/sites/aaib/publications/bulletins/october_1996/eon_502118.cfm

There was some evidence that the wood/metal composite mainspar was
slightly corroded in this glider, but it is still unlikely that it
would have failed if launched on the correct weak link.

If you want to avoid weak link breaks using a single link, perhaps you
should change the link after 100 launches, or monitor its condition.
The Tost links have a hole drilled in them, like a tensile test piece,
and this will show signs of distorting or cracking before it fails.

Derek Copeland


On Jun 2, 2:53*pm, "Tim Mara" > wrote:
> unbelievable! especially since a weak link is such an easy thing to add,
> especially for ground launching!
> you might be quite amazed at the numbers of pilots who call me asking what
> the "proper weak link" should be when it is such a fundamental question and
> one that every prospective student pilot needs to know even before taking a
> practical test for a private pilot certificate!
>
> using the TOST weak links is easy and the reserve weak link makes a lot of
> sense since ALL weak links fatigue in time and become weaker before actually
> breaking.the idea of the reserve weak link is so that when this happened and
> the main weak link fails from fatigue the reserve link will hold under
> normal loads and the launch is still completed without an actual failure but
> the broke link is then visible for the next launch (we check these before
> each launch .right? ((you are supposed to) and you know then to replace the
> broken link before continuing with another launch. simple to use, and even
> simpler to change from one weak link strength to another as needed by using
> the notch connectors or similar attachment.you can see more on my website
> pagehttp://wingsandwheels.com/page30.htm
>
> regards
> Tim Mara
>
> Please visit the Wings & Wheels website atwww.wingsandwheels.com
>
> "T8" > wrote in message
>
> ...
> On Jun 2, 4:43 am, Paul > wrote:
>
>
>
>
>
> > Currently the club that I am part of don't seem to be too concerned about
> > the safety aspects of using the correct weak links for winch launching
> > and I'd like to know how safe it is.
>
> > Currently I see two issues with the winch launching:
>
> > 1. Sometimes a weak link is not used at all. The gliders are attached
> > directly to the winch cable (via drogue chute and various connectors).
>
> > 2. When a weak link is included in the cable (only a primary link - no
> > reserve link) it is used for all glider types (G102 Astir, G103 Twin II,
> > ASW20, LS4) and I'm not even sure what the breaking strain is. My guess
> > is it's a Tost #1 black (1000 daN) weak link but that's hard to tell
> > because its weathered and the protective sleeve obscures the Tost number.