Today's Message Index:
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1. 01:03 AM - Re: Post curing response (John Wighton)
2. 01:29 AM - Re: Re: Post curing response (Brian Davies)
3. 03:36 AM - Re: Post curing response (John Wighton)
Message 1
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| Subject: | 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
Message 2
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| Subject: | Re: Post curing response |
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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Message 3
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| Subject: | Re: Post curing response |
Brian, thanks for your comment.
I am not aware of any negative influence that a fully cured structure can provide.
Post-curing of most Europa builds will occur in-service, hot days and heat soak
can reach surface temperatures easily exceeding 55C. Prolonged exposure would
compensate for the lack of higher temperatures, eventually. Hence most Europa
will achieve something close to full strength over time. But that is hardly
a controlled process.
Due to the adoption of generous CSF our Europa aircraft are designed to load levels
rarely, if ever, encountered in service. Crashworthiness aside, the Europa
is somewhat over-engineered.
Given that temperature exposure up to and beyond the Tg is not desireable, as chemical
changes occur. Core temperature range is often cited as a limitation.
However, aircraft materials should have the ability to work from -30C to +80C
without degradation. Otherwise operational limitations will apply.
It's a bit like having a car paint job and driving off before the paint has fully
cured. Why would you? Sure, the paint will cure eventually, but in the meantime
it is soft and will incur scratches and other damages. Maybe an imperfect
comparison but hopefully you see what l am talking about.
The tub to lower shell joint, top to bottle shells and wing pin reaction locations
all need to achieve full strength. Post-curing to the manufacturer's process
instructions is therefore my recommendation.
--------
John Wighton
Europa XS trigear G-IPOD
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=496602#496602
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