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1. 02:03 AM - Re: Re: Post curing response (Kevin)
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| Subject: | Re: Post curing response |
Phil ,
All layups are post hardened, either with local temperature controlled heating
(and logger in case of power failure etc.. for a few pounds .. graph can be downloaded
on to computer ) ..that is what I did for Tri Gear bracing ( converted
from Mono after 30 hours) ..
You can go the alternative route and build an insulated box for fuselage , and
post harden (cure) everything in one go..(control surfaces ,wings , then fuse
depending on stage completion ).
Use peel ply on internal areas like fuel filler cobra to extract excess resin /
as post build temperature differences can pull and deform slightly showing as
a slight deformed external skin.
Correct support of components is important, as is keeping within Europa build manual
temperatures, ( and resin manufacturers guidelines as there may be differences
due to specification changes over the years) ... do not be tempted to bump
up the temperature beyond spec .
Statement above is important of you could end up with warping twisting , deamination
and damage to cores ..
Manufacturers specifications are the primary references.
Make a mini test oven for your heaters controllers and loggers , make some test
components...chocks , cradles , special rigging kit .. and test and tune before
doing critical parts.
Post hardening allows lay ups to be worked without clogging tools.
Also when filling control surfaces ..sanding back the filler is less draggy craggy
on your favourite abrasives.
These practices are from the hard stuff Slingsby glider repair manual , the UK
bible for composite construction and maintenance , cure cycles of 18 to 24 hours
are usual ..
Enjoy
Kevin Burns
Sent from my iPad
> On 2 Jun 2020, at 09:28, Brian Davies <brian.davies44@gmail.com> wrote:
>
>
> Hi John,
>
> I recognise your superior knowledge on this subject but is it wise to
> recommend that Europa builders in particular post cure their entire
> fuselage? There is now considerable in service experience with Europas that
> have not been subject to this treatment and I am not aware of any safety
> issues resulting from lack of post cure of the fuselage. I would also apply
> the same logic to the XS wings that use factory moulded parts.
>
> Regards
>
> Brian Davies
>
> -----Original Message-----
> From: owner-europa-list-server@matronics.com
> <owner-europa-list-server@matronics.com> On Behalf Of John Wighton
> Sent: 02 June 2020 09:03
> To: europa-list@matronics.com
> Subject: Europa-List: Re: Post curing response
>
>
> Post-curing is essential to achieve optimal bond strength. This applies to
> laminated parts and also part to part glued joints. The regime for the
> post-curing depends on the system used. Some systems achieve full strength
> when exposed to RT (ambient 20 deg C) other require higher temperatures.
> Generally higher temperatures result in full post-cure properties being
> achieved in a shorter time.
>
> Ideally, Europa (composite airframes in general) should be post-cured in
> their entirety - achieved in an oven with a controlled environment. A
> Paintshop facility can provide these conditions.
>
> It should be noted that the Achilles heel of composite aircraft (at least
> those approved via the LAA) has been the requirement to use a 'Composites
> Super-Factor' (see LAA TL 1.17). This takes into account the significant
> variability in composite strength, stiffness, etc at non-RT conditions. It
> also includes a variability factor that accounts for variations in the
> processes of laminating, jointing, etc. This CSF can be as high as 1.50. A
> reduction in CSF may be negotiated, this is more likely if documented
> processes and post-cure is followed. Recent discussions with LAA
> Engineering indicate that CSF of 1.20 may be possible in some circumstances.
> This can have a significant influence on RFs (margins of safety)
> calculations and even MAUW determination.
>
> My advice to Europa builders is to post-cure their entire airframe. Survey
> the airframe to ensure no items are present that will degrade at the chosen
> post-cure temperature.
>
> A typical post-cure process will look something like the following (BUT
> adhere to the supplier instructions and limitations):
>
> 1. RT to 80C, ramped up at 1-2C per minute.
> 2. Hold (dwell) for 120 mins (typically 80C).
> 3. Ramp down at 1-2C/min.
>
> The structure should be free (no clamping or holding things down), I would
> assemble the airframe but this is rarely possible.
>
> --------
> John Wighton
> Europa XS trigear G-IPOD
>
>
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=496600#496600
>
>
>
>
>
>
>
>
>
>
>
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