Use of weak links

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

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 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

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

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

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

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.

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

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 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