KA6E and Foka 4 comparable metal ships - Laister Nugget LP15

My club has some problems with a Ka-8. It seems the gluing of the spar
and the torsion box has been done with better glue than that of the
ribs. It has been done with another glue type: dark brown for the
former (probably Aerodux), yellow/very light brown for the latter
(Kaurit?). The latter type of glue seems to fail easily nowadays.

However, metal structures are known to fail, too, and often without
warning, by metal fatigue. Normally, sailplanes are made over strong in
critical metal components, just to allow for this phenomenon, but it's
not foolproof.

Let me get this straight, you're complaining that the LP15's cockpit
is too big? That's a complaint I have not heard before about any
glider.

And yet, the Schempp-Hirth people are producing their "a" model
fuselage (Discus a, Ventus a) for that reason, some competition pilots
complaining that by making their cockpits too big (like the Standard
Cirrus), they were wasting possible aerodynamical advantages... These
fuselages are advertised for slim pilots not bigger than 1.75 m.


--
stephanevdv
------------------------------------------------------------------------
Posted via OziPilots Online [ http://www.OziPilotsOnline.com.au ]
- A website for Australian Pilots regardless of when, why, or what they fly -

stephanevdv wrote:
My club has some problems with a Ka-8. It seems the gluing of the spar
and the torsion box has been done with better glue than that of the
ribs. It has been done with another glue type: dark brown for the
former (probably Aerodux), yellow/very light brown for the latter
(Kaurit?). The latter type of glue seems to fail easily nowadays.
There was / is a general AD out for the Ka range of gliders to check all of the
joints (presumably where the lighter glue is) To my knowledge there have been
three failures of Ka wings due to glue joint failure. Two were on overpowered
winch launches, the third one the pilot lost much of his starboard wing behind
the airbrakes in flight, but landed safely. This appears to be a problem
specific to the glue used on these gliders, their storage conditions and their
structure.

Phenolic glues, like the more modern composites have a very long life. All
phenolic resins are black or brown, strong but not terribly flexible. The latest
epoxy resins are enormously strong, and seem to have indefinite life. They glue
buildings together with the stuff these days.

The main indicators of glue problems seem to be if the joints have been subject
to moisture over a long time.


However, metal structures are known to fail, too, and often without
warning, by metal fatigue. Normally, sailplanes are made over strong in
critical metal components, just to allow for this phenomenon, but it's
not foolproof.


Let me get this straight, you're complaining that the LP15's cockpit
is too big? That's a complaint I have not heard before about any
glider.


And yet, the Schempp-Hirth people are producing their "a" model
fuselage (Discus a, Ventus a) for that reason, some competition pilots
complaining that by making their cockpits too big (like the Standard
Cirrus), they were wasting possible aerodynamical advantages... These
fuselages are advertised for slim pilots not bigger than 1.75 m.

And I am eternally grateful to Klaus Holighaus for the armchair in my Std
Cirrus, even if it loses a little on L/D...


--
stephanevdv
------------------------------------------------------------------------
Posted via OziPilots Online [ http://www.OziPilotsOnline.com.au ]
- A website for Australian Pilots regardless of when, why, or what they fly -



--
Bruce Greeff
Std Cirrus #57
I'm no-T at the address above.

In message , Bruce
writes
stephanevdv wrote:
My club has some problems with a Ka-8. It seems the gluing of the spar
and the torsion box has been done with better glue than that of the
ribs. It has been done with another glue type: dark brown for the
former (probably Aerodux), yellow/very light brown for the latter
(Kaurit?). The latter type of glue seems to fail easily nowadays.
The light brown glue is similar to casein. There were some produced
with both but most were one or the other. The dark brown aerodux ones
are later.
There was / is a general AD out for the Ka range of gliders to check
all of the joints (presumably where the lighter glue is) To my
knowledge there have been three failures of Ka wings due to glue joint
failure. Two were on overpowered winch launches, the third one the
pilot lost much of his starboard wing behind the airbrakes in flight,
but landed safely. This appears to be a problem specific to the glue
used on these gliders, their storage conditions and their structure.

The earlier Ka gliders used a glue called Kaulac or Kaurit (Forgive the
spelling as I can't remember the correct one). This was similar to
casein with all of the drawbacks that casein has. If they are stored
damp then they will, after some time fail. At some point in the Ka6
production they switched to Aerodux, or something like it, and the glue
won't fail until a long time after the wood.

Recently in the uk there have been a series of mandatory inspections for
all early Ka (K4, 6, 7, 8 don't know about 13) types. This was
triggered in part by a fatal accident involving a Ka7, some of the
checks preceded this. These checks haven't, as far as I know, thrown up
many problems and the most likely causes of most problems have been
traced to bodged repairs rather than glue/wood deterioration.

I have just repaired/rebuilt a 1952 aircraft (T31) that had several
bodged repairs made from Aerodux but through poor joint prep the joints
were very weak. In older aircraft that have accumulated repairs this is
a more likely source of failure rather than the original construction.

Phenolic glues, like the more modern composites have a very long life.
All phenolic resins are black or brown, strong but not terribly
flexible. The latest epoxy resins are enormously strong, and seem to
have indefinite life. They glue buildings together with the stuff these
days.


The main indicators of glue problems seem to be if the joints have been
subject to moisture over a long time.

Yes, the point of failure has changed over time though. With pre
synthetic glues the most likely failure was the glue itself (glue rot
and so on) whilst today it is more likely to be the wood through damp or
poor glue adhesion through poor joint preparation.

Cheers

Robin

However, metal structures are known to fail, too, and often without
warning, by metal fatigue. Normally, sailplanes are made over strong in
critical metal components, just to allow for this phenomenon, but it's
not foolproof.


Let me get this straight, you're complaining that the LP15's cockpit
is too big? That's a complaint I have not heard before about any
glider.
And yet, the Schempp-Hirth people are producing their "a" model
fuselage (Discus a, Ventus a) for that reason, some competition pilots
complaining that by making their cockpits too big (like the Standard
Cirrus), they were wasting possible aerodynamical advantages... These
fuselages are advertised for slim pilots not bigger than 1.75 m.

And I am eternally grateful to Klaus Holighaus for the armchair in my
Std Cirrus, even if it loses a little on L/D...

--
stephanevdv
------------------------------------------------------------------------
Posted via OziPilots Online [ http://www.OziPilotsOnline.com.au ]
- A website for Australian Pilots regardless of when, why, or what they fly -




--
Robin Birch