Buying a glider, advice on type and prices

On Tuesday, August 30, 2016 at 11:53:20 PM UTC+12, Dan Daly wrote:
The site says something like approved life of 3000 hours with extensions so maybe that's the one that's now been upgraded to 12,000 hours. (will check) That's one reason I was looking for a more recent model in case GRP gliders do have problems in later life. Just about anything will outlast me but I'm thinking resale value.

http://szd.com.pl/downloads/4fdeffe8...l-10039816.pdf is the document which extends the life of all SZD-55 to 12k. The associated Flight Manual must be amended with the 2012 changes, which is noted at the end of the EASA document. Mainly they talk about what inspections have to be done periodically, and change the bits of the manual that talk about the authorized lifespan of the glider.

Most gliders get an initial 3,000 hr approval, then as they approach that, they are assessed by the factory to see if they have problems. If not, additional 3,000 hrs. As they approach 6,000, same, etc., until design life is reached. I don't know what the design life of Schempp-Hirth, Schleicher, etc are (I know ASK-21's are at 18,000 hrs). I think of most GRP gliders as having infinite lives, though gelcoat must be refinished periodically.

OK .. *why* must gelcoat be refinished periodically?

I suppose eventually it might start letting moisture through into the structure, but I suspect most people are refinishing it at less than 50% (maybe much less) of its potential protective lifetime for purely aesthetic reasons.

Does cracked gelcoat have much of an effect on aerodynamics? One that someone other than a top competition pilot would notice?

Aerodynamics isn't the issue - gelcoat failure can progress until it's a structural issue.

There are many early Cirrus & Libelle (amongst others) from the early / mid 70s that still flying with original gelcoat without any signs of failure.

Nick.

On Wednesday, August 31, 2016 at 5:23:44 AM UTC+9:30, Bruce Hoult wrote:
On Tuesday, August 30, 2016 at 11:53:20 PM UTC+12, Dan Daly wrote:
The site says something like approved life of 3000 hours with extensions so maybe that's the one that's now been upgraded to 12,000 hours. (will check) That's one reason I was looking for a more recent model in case GRP gliders do have problems in later life. Just about anything will outlast me but I'm thinking resale value.

http://szd.com.pl/downloads/4fdeffe8...l-10039816.pdf is the document which extends the life of all SZD-55 to 12k. The associated Flight Manual must be amended with the 2012 changes, which is noted at the end of the EASA document. Mainly they talk about what inspections have to be done periodically, and change the bits of the manual that talk about the authorized lifespan of the glider.

Most gliders get an initial 3,000 hr approval, then as they approach that, they are assessed by the factory to see if they have problems. If not, additional 3,000 hrs. As they approach 6,000, same, etc., until design life is reached. I don't know what the design life of Schempp-Hirth, Schleicher, etc are (I know ASK-21's are at 18,000 hrs). I think of most GRP gliders as having infinite lives, though gelcoat must be refinished periodically.

OK .. *why* must gelcoat be refinished periodically?

I suppose eventually it might start letting moisture through into the structure, but I suspect most people are refinishing it at less than 50% (maybe much less) of its potential protective lifetime for purely aesthetic reasons.

Does cracked gelcoat have much of an effect on aerodynamics? One that someone other than a top competition pilot would notice?

On Tuesday, August 30, 2016 at 4:42:09 PM UTC-4, wrote:
Aerodynamics isn't the issue - gelcoat failure can progress until it's a structural issue.

There are many early Cirrus & Libelle (amongst others) from the early / mid 70s that still flying with original gelcoat without any signs of failure..

Nick.

Different gelcoats than today's, due to environmental concerns for the workers. Agree older gel held up better, unless exposed to a lot of temperature swings (wave flights without temperature stops every 5000'). Newer std class - which is what is being discussed here - have gelcoat issues. PU paint is preferable, in my opinion. I can also think of several original Cirrus which required full refinishes in their lives.

On 8/30/2016 2:42 PM, It was written:
Aerodynamics isn't the issue - gelcoat failure can progress until it's a
structural issue.

In the spirit of seeking genuine knowledge - and readily acknowledging
widespread *concern* that cracking/flaking gelcoat can "somehow" morph into a
"premature" structural issue - can anyone cite solid information (data, links,
etc.) shedding light on the mechanism(s?), location and quantity of UV-exposed
plastic sailplanes thrown onto the garbage heap after failing structural
tests, etc.? It's a serious - not rhetorical - query.

There's plenty of engineering data, as well as "common-sense/observational
data", around indicating UV is a catholic attacker/degrader of all manner of
materials, but have sailplane manufacturers, or (say) the LBA, or anyone else,
set about obtaining such data for GRP/CRP sailplanes?

Hard data eagerly welcomed!

Bob W.

Failed gelcoat absolutely "prints" down into the glass/epoxy substrate. We've just refinished two gliders in our club which were left to go beyond minor crazing to full-on gelcoat failure. Once the gelcoat is totally stripped, you're left with visible lines in the glass/epoxy. Under a 4x loupe you can see that there is an edge to these lines where there are small voids in the epoxy.

Does this materially affect the integrity of the wing/fuselage/control surface structure? That's beyond my pay grade.

Gerhard Weibel's take is as follows (from the Schleicher Technical Note on "paint cracks"):
Owing to the UV-radiation the gel coat of the paint surfaces grows
brittle and shrinks; at the same time the UV-light destroys paint ingredients.
So moisture (rain, dew) working in on long term will wash the
decomposed paint ingredients out off the paint. The paint starts chalking
and gets hairline cracks owing to the concurrence of embrittlement
and shrinkage. Furthermore, these hairline cracks gather dirt
which through its aggressive effect and its stronger heating-up from
sun radiation further precipitates the degradation of the paint. Owing
to this the intended protective effect for the fiber composite structure
against moisture and UV-radiation is no longer granted.

Certainly a good care with hard wax can slow down the above process
distinctly, but it cannot be stopped completely. For this reason a
repainting of the aircraft will always become necessary at some point
of time.
However, we point out explicitly that paint cracks - even deep cracks -
do not represent damages to the aircraft structure if as of their first
appearance immediate correct maintenance and care is given furthermore
to the aircraft.
As all the outside skin of the aircraft is dimensioned for stiffness, there
are no critical mechanical strength problems, even if some cracks
have gone down into the fiber composite structure and have already
attacked the resin matrix base.
The unknown ageing effects caused by the influence of moisture and
UV on the unprotected fiber composite structure are more dangerous.

P3

On Tuesday, August 30, 2016 at 7:20:26 PM UTC-4, Bob Whelan wrote:
On 8/30/2016 2:42 PM, It was written:
Aerodynamics isn't the issue - gelcoat failure can progress until it's a
structural issue.

In the spirit of seeking genuine knowledge - and readily acknowledging
widespread *concern* that cracking/flaking gelcoat can "somehow" morph into a
"premature" structural issue - can anyone cite solid information (data, links,
etc.) shedding light on the mechanism(s?), location and quantity of UV-exposed
plastic sailplanes thrown onto the garbage heap after failing structural
tests, etc.? It's a serious - not rhetorical - query.

There's plenty of engineering data, as well as "common-sense/observational
data", around indicating UV is a catholic attacker/degrader of all manner of
materials, but have sailplane manufacturers, or (say) the LBA, or anyone else,
set about obtaining such data for GRP/CRP sailplanes?

Hard data eagerly welcomed!

Bob W.