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
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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