Article
by Steve Uzochukwu. Photos ©: Steve Uzochukwu, Ojovolador, Porcher
Industries. 2005.
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Research
in action
The R Team Palsecam was formed to conduct practical research
about the gliders material to help improve them. The team
pilots fly gliders specially made with new cloths, and study
their behaviour and aging after 100 hours of use in various
styles of flying (acro, competitions, XC) and different conditions
of weather and launches (alpine, tropical, seaside). Every
100 hours, some of the cells are removed and taken to the
laboratory at Porcher Ind., and new experimental cloth is
used to replace them, as you can observe in the picture above
(pilot: Charles Cazaux; glider: Gin Boomerang 4; place: La
Palma island in Canarias).
Porcher is one of the partners of this pioneering project.
+Info: www.palsecam.fr |
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Sometimes
we pilots take things very much for granted, and only on standing
back can the enormity of a technical accomplishment hit home. A
flying machine with no rigid structure, weighing less than one tenth
of its pilot takes to the skies. The whole lifting surface is made
of a material that weighs less than 50 gm/m2 [less than 2 oz/sq.
yard in old money]. That material is capable of supporting a 12
G load [on a glider like the Gin Gangster] if need be, without failing,
and is made of much thinner cloth than the average T-shirt. The
material flies for many hundreds of hours nowadays, despite the
fact that on small sites in the UK 15 years ago the airtime of similar
machines was measured in minutes or single hours. Their present
life runs to 5 or six years, not the two seasons we expected in
1989.
We
are talking about the amazing technological achievement that is
paragliding cloth. We usually ignore this technical achievement,
and it only becomes a topic of conversation when a negative issue
like unexpected glider demise, usually caused by porosity, comes
to light. In the last two years, one of the biggest manufacturers
of paragliding cloth, NCV [Nebon Carle-Vassoilles],
part of French group Porcher Industries, has sought
to help in the education of pilots as to how the cloth used in their
gliders is made, tested, developed and needs to be cared for. NCV
make the cloth colloquially referred to as "Porcher
Marine" but which is known in the technical textile
industry as Skytex. NCV use the name Skytex for
all the cloth they make which is specially designed for use in paragliders.
Reporter Steve Uzochukwu was invited to view the whole manufacturing
process in a tour of NCV facilities in the area between Lyon, Chambéry
and Grenoble in France.
Paragliding
cloth has demanding requirements. It needs to be light,
and capable of withstanding very high loads. It must not leak air,
as it is air pressure that keeps the glider inflated, and generates
lift. It must retain its qualities for a very long time, look nice
and be as cheap as possible. When all that's said and done, we like
to fold it away very tightly, without any marks or creases affecting
the cloth. These demands have evolved along with paragliding itself
from the first retrimmed ram air free fall parachutes, made from
the zero porosity nylon of which NCV was already a manufacturer.
The first dedicated paraglider makers also tried using spinnaker
cloth, also made by NCV. Neither cloth was ideal for the requirements
of paragliding, so these manufacturers came to NCV with a requirement
for cloth specific to paragliders. NCV obliged, and they have been
developing dedicated materials for paragliding ever since. This
kind of specialised technical textile development is at the centre
of the NCV portfolio, as they produce synthetic textiles for a wide
range of applications, mostly safety based. Products that use NCV
textiles include car airbags, bullet-proof vests, parachutes and
spinnakers.
The
overall involvement in paragliding cloth for NCV can be divided
into development, production and quality
control. The technical textiles market involves high levels
of Research and Development, as fierce competition for market share
exists. The textiles coming out of the R&D process have to be
capable of mass production and delivery to tight time scales in
an industry that is quite seasonal for demand. Quality control has
to ensure that the product consistently achieves a certain standard,
and that any finished roll of cloth can be traced all the way back
through every machine used to make it and to every constituent ingredient.
To
understand the production of cloth, it's easiest to follow the thread
[or yarn] from its entrance into the factory to its exit into the
free flying world as cloth destined for a manufacturer.
At each point we can see what is happening and how the stage contributes
to the properties of the finished product. We'll look at the production
side of the operation first then look into how the development has
led to the product we have today and its aspirations for the product
of the future. After that a quick description of the quality control
process will be followed by some advice from NCV about keeping our
gliders in good condition by extending the life of the material
they are made from.
Paragliding
cloth begins its life at NCV by coming into the plant as 6.6
polyamide yarn, made by globally renowned company Du
Pont [also known as Invista] and delivered on bobbins each
with 550 km of thread in one continuous piece. Du Pont/Invista
invented the yarn used nearly 70 years ago and christened it Nylon,
its brand name to this day. 10 km of this wonder thread weighs just
33g. Each thread is made up of ten individual filaments of Nylon.
The thread already contains additives to inhibit UV degradation,
one of the main factors in the longevity of the finished cloth.
Weaving
is a centuries old process, which involves the creation of a fabric
from the interlacing of yarn. Originally done by hand, the mechanisation
of weaving in the 18th and 19th centuries revolutionised the creation
of fabrics, allowing huge amounts to be made in a very short time
and space with very little error or imperfection in the finished
product. Just as well, as a paraglider averages just under 30m2
on both top and bottom surfaces, with a finished glider consuming
about 100 m2 of cloth after ribbing is taken into account.
The
process starts in the creation of a master beam 10,000 threads wide,
across which the looms will thread the filling yarn to produce the
finished cloth.
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To
create the master beam, sub beams of 1,000 threads wide are
created first. 1,000 bobbins sit on the creel and the sub
beam is wound from these, and it is at this point in the process
that the yarn is laser examined to check the integrity of
the thread and to log breaks in the individual filaments. |
| Yarn
being combined into the sub beam from which the main beam
is made. |
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Let's
talk about some terms here, as they are needed
for the rest of the explanation of the process. The direction
of the threads in the beam, which is the same as the direction
along the finished roll of cloth [lengthways], is called the
warp direction. The filling yarn, which is the thread
that goes across the finished roll of cloth [widthways], does
so in the weft direction. Cloth manufacturers
quote the strength/elasticity of the cloth in both these directions.
They also quote strength & stretch in another direction,
the bias, as the direction at 45 degrees
to both warp and weft. |
Main
beam creation from sub beams.
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The
first time a particular batch of cloth is made to a certain
weave all the threads [10,000 in all] are manually inserted
into the needles on the loom. It's at this stage that the
actual detail of the weave is incorporated into the cloth.
Ripstop is actually a weaving pattern,
created by breaking up the alternation of one thread under
the filling yarn, and one over. This results in a double
or triple thread at regular intervals, causing a bunching
or ruching of the cloth as an object tries to cut or tear
through it and preventing the propagation of the tear. Ripstop
offers improved resistance to tearing without the penalty
of a heavier cloth.
Looms
can use a traditional needle [a shuttle] to pass the filling
yarn through the beam, or more recently use either a jet of
air or water to thread the filling yarn. |
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Skytex
is woven by the air jet method. All Skytex
cloths use 10,000 threads in the warp direction,
and the weight of the cloth is decided by the packing density
of the filling yarn. |
The
cloth produced comes in four weights at the
end of the weaving process, Skytex 36, 40,
45 and 55. All these numbers
refer to the weight per square metre, and
the 36 and 40 will be sold as 9017, with the 45 being referred
to as 9092 and the 55 as 9112. The weights of the cloths and
the coatings they come with are summarised in the table. |
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The
cloth is wound onto a master roll at the end of the weaving
process. At this point the raw cloth, known as greige material
has no colouring, and allows air to pass through it. It needs
to be dyed. Even white material requires dyeing, and it must
be washed first to remove any residue from the weaving process.
It then undergoes the colouring process after which the dye
must be fixed. Colours are chosen by NCV
for their UV stability, and great strides
have been made in this area with colours like black or some
reds that were unusable for paragliding cloth ten years ago
now being both suitable for use and amongst the most UV resistant
colours. The dyeing process improves the durability
of the cloth and contributes to its dimensional stability.
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White
cloth makes up about 50% of the total sold. White and the
other colours are made in batches, with a washing process
followed by dyeing and fixing. After the fixing process, and
a check to see that the colour has become fast, the material
passes through an oven to further fix the dye and to dry out
the cloth. The rolls of cloth, now with the colour needed
but without any coating, undergo vigorous quality control
for defects in the physical nature of the material itself
as well as the consistency of the colour. A lot of this quality
control is of a manual nature, as most automatic scanning
processes do not work well with ripstop material. Samples
of material undergoing testing in the laboratory do so in
an environment carefully controlled for temperature and humidity
24/7, with the samples being taken into that environment at
least 24 hours before any test is performed.
The rolls of cloth now leave for Griffendux,
another Porcher Company across the road from NCV. Griffendux
is also part of the NCV Technical Textiles division and their
role is to coat the cloth, and the coating
gives the cloth a number of qualities that will change it
very significantly.
The cloth is very strong in the directions of warp and weft,
as pulling in either of those directions engages threads that
go across or along the cloth. In both directions the threads
of the yarn resist any deformation directly. However, if we
pull hard on the bias, the resulting strain
relies on the weave rather than the threads directly, and
it tends to deform more in this direction. Also, the cloth
allows air to pass through it relatively easily, which for
paragliding is useless. The addition of a coating
to the cloth does two major things - it makes the cloth far
more resistant to elongation or deformation
on the bias, and it makes the cloth airtight.
The coating also has the ability to reduce the effects of
ageing on the cloth, allowing it to retain tear strength and
resistance to stretching despite exposure to sunlight and
thousands of loading and unloading cycles. NCV specify different
coatings for different areas of use in a paraglider, with
four main types being used: Firm, Medium, Water repellent
and Medium Mark 2. |
Washing
and dyeing machine |
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After all this effort to make top quality
cloth, NCV have some advice for pilots on how to keep
their gliders in top condition:
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·
Avoid all unnecessary exposure to sunlight - put your
wing away when not in use.
·
Don't drag your wing over the ground or tread on it.
·
Don't fold your wing too tightly and be sure to fold
the leading edge as per instructions.
·
Check when folding away your wing for insects or other
foreign bodies and don't leave them in the wing.
·
Leaving your glider locked away in a car boot in strong
sunlight can lead to extremes of heat reducing the life
of the wing significantly.
·
Only fold your wing away when it is completely dry,
and store it in a cool, dry place with the bag open.
·
To clean your glider, spread it out on a clean, dry
surface, and use Savon de Marseille [or similar olive
oil based natural soap] and a wet sponge. Do not use
abrasives or solvents.
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The NCV web site can be found at:
www.ncv.fr
*The
author of this article, Steve Uzochukwu (UK), is a Freelance
Broadcast Technician, free-flyer of different aircrafts
and occasional writer for Skywings and Cross Country magazines.
You can visit his website: www.steveu.org
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Firm
[E29A]
This
coating has strength and low elongation as the priorities,
because it is used for ribs. These qualities
can be optimised at the expense of porosity and abrasion resistance,
as the ribs never come in contact with the ground nor are
they responsible for air retention.
Medium
[E38A, E68A]
This
is a medium finish coating used for cloth destined for both
upper and lower surfaces, and some use in
ribs, usually the lighter unsuspended ones. This coating has
to be good in all areas, considering the amount of UV exposure
and contact with the ground the cloth may have. E68A coating
is slightly lighter than E38A [36gm/m2 v 40gm/m2] because
of additional processing on the cloth, hence the choice of
E68A as the finish for the 9017 cloth for a mountain glider
like the Gin Yeti.
Water
repellent [E77A]
Another coating for general use in the upper and lower
surfaces, with the added quality of being water repellent.
All
the above coatings are applied to the cloth in a process that
uses organic solvents.
Medium
Mark 2 [E85A]
This
is a new coating developed over the past 4 years by NCV. It
combines the need for longer life and resistance to all forms
of degradation with the mandate coming from the European Union
for all industrial processes to be more environmentally
friendly. To satisfy the green requirement, this
coating uses a water based rather than an organic solvent
application process. This new coating vastly improves
the life of cloth it is applied to. Resistance to UV degradation
and performance in washing/flutter tests also show a great
step forward. A comparison for the new coating compared to
the old can be seen in the graph for flutter and washing/tumbler
tests on the left. This coating is used on cloth
in Aerodyne, UP, Gin and FreeX gliders.
All
the coatings are applied by a process using a reservoir of
the coating dissolved in solvent as the cloth passes by a
sharp edge, resulting in a layer of coating a few microns
thick. The coated cloth is then blown dry to remove the solvent
and the finished paraglider cloth is ready. The last two checks
involve the use of a fabric table to check the cloth for flatness
and uniformity and then a visual check for defects.
The
paragliding cloth produced by NCV has not got to the stage
that it is at now without a lot of Research and Development.
The constant demands coming from the manufacturers ask for
cloth that is longer lived, lighter, stronger and cheaper.
This involves constant development of yarns, weaving methods
and coatings which undergo standard tests including measurement
of elasticity, elongation, and tear strength. Other tests
more specific to paraglider cloth include such harsh measures
as constant exposure to very high intensity UV light, repeated
washing in a machine, scrubbing and a flutter test where the
cloth is artificially fatigued on a small windmill at 90 km/h.
Even
when a new coating, for instance, offers advantages over existing
ones that coating must be integrated into the manufacturing
process in such a way that it can be produced reliably and
economically to the existing quality standards or higher.
At the moment the new E85A coating is generally
only offered on 45 gm/m2 [9092] cloth, but at extensive testing
programme is ongoing to finalise the large scale manufacture
of the lighter 9017 cloth with the new coating. One of the
launch customers for the 40gm/m2/E85A based cloth has been
Nova, who have used it for the undersurface
of the Syntax and are going to use it for
the whole body of the mountain version of the same glider.
New fabrics are constantly being developed by NCV R&D
engineers. There is definitely a trend towards lighter
and lighter fabrics. This year, for the first time
since the release of the 40gm/m2 cloth 5 years ago NCV has
sold more Skytex 40 than Skytex 45.
Quality
control is also embedded into the manufacturing process. Direct
examination of the product at key stages is combined with
the taking of samples to test to destruction in the laboratory.
At every stage a series of numbers on the product allow a
complete trace of the product path back to every constituent
ingredient used and every person or machine involved. A sample
of every roll of cloth leaving the factory is archived. NCV
point out that with some 80% of their material being used
in safety applications, a reputation for quality is essential
to their continued status as a market leader in the technical
textiles field. |
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