飞机蒙布工艺(Aircraft fabric process)
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飞机蒙布工艺（Aircraft fabric process）
Common
problems in skin fabrication
Common
problems in skin fabrication
Ron
Alexander
It's a big deal to make cloth
skins for airplanes. The reason
is very
simple, you spend energy on the plane Months and
years
pass by. production, but now it has to
use a cloth to those
skilled hand structure
wrapped up, most people only see the
plane of
the skin. Laying skin on who is a challenge, no
matter
whether you have the experience of the
past, you only know the
need to fix it, what
people say is usually outside the body to
determine the quality of the decoration. This
is not only
related to the sense of
achievement of the laying process, but
also
with the cost and time spent in the production.
The first
mention of a wake up, then don't
petty suffer a great deal. Over
the years,
I've been listening to the enthusiasts and
repairer
of airplanes, nagging about how to
cover the body - really show
the only part of
the airplane - dig out the money. Now is not
the time to save money. Iron down the heart
and spend the money
on the skin to keep it as
high as the rest of the airplane. Make
an
envelope for a J-3 CUB size aircraft, and it costs
about 2500
to 3000 dollars, regardless of the
process. If someone quotes
very much less than
this number, then he is not finished. When
we
finish the work, we still get so much money after
finishing
the work. Well, if you do it
yourself, you can save about $$10000.
Yes,
that's right. Most experts charge between 8000 and
12000
dollars.
Fabric fabrics
and coatings will last about 15 to 20 years if
they are given in accordance with the fabric
instructions. The
length of life is related to
the exposure of the aircraft to
sunlight and
other factors. Regardless of the condition of the
aircraft skin, most of the aircraft owners
will check the
aircraft inside the situation
at 20 years.
It's not a light thing to
give the airplane skin, or you won't
see why
the skin and coating of those airplanes are always
in
a state of love. Of course, this is much
more than a little
trouble those unsightly. I
believe you have seen the scaly
coating,
Aeronca Champ or J-3 Cub seen the tilt of the tip
(here
can not raise new set of lift). What is
the cause of these common
problems? Is it
caused by the type of skin laying? Rarely for
this reason. Because each skin laying type has
its own
advantages. Again, if you follow the
instructions strictly,
there's usually no
problem.
So why do we have so much
trouble? This is what I'll mention
in this
article and related articles -- common fabric
skinning
problems and solutions.
In
writing this article, I exchanged views with Jon
Goldenbaum
of Poly-Fiber (polystyrene) Company
and asked him to list the
fabric skin problems
most frequently mentioned by customers.
These
problems are not only related to the addition
process of
their products, but also exist in
most other types of existing
fabric skin.
Whether you use polyurethane paint, nitro and Ding
Suanji coated cloth or Poly-Fiber products,
the basic problems
are the same. In fact, most
of the processes are very similar,
but when it
comes to chemicals, the situation is different.
The
important point is that no matter
what kind of fabric skin,
should be strictly
in accordance with the requirements of the
instructions processing, do not try their own
way, or confusion
of different fabric skin
production process. For example, don't
use
Grade A tape tape in Ceconite
Spray the
nitrocellulose lacquer on the card skin fabric or
on
the polystyrene fabric. These are common
causes of trouble.
If you're skinning a
production aircraft, you have to do it in
strict accordance with the skin fabric
construction manual.
Mass aircraft skin
processing methods need to be approved by
the
Federal Aviation Administration (FAA). It must
also have
a supplementary model qualification
certificate (STC),
The certificate
specifies the method of skinning that can be
used to replace the original skin of the
aircraft. This
supplementary model certificate
(STC) is not allowed to confuse
the
manufacture methods of different fabric types of
skin.
Interestingly, the certificate only
specifies the silver
primer (UV protection
coating) for the skin, but there is no
limit
to the coating of the outermost layer of the skin.
If
you're skinning an experimental aircraft,
how is it legal?. I
have to emphasize that,
even so, you should choose the STC
approved
production program. It's common sense that your
experimental aircraft, like a production
aircraft, flies over
the same air, and it
carries people. Just because you can do
whatever you want, you should avoid
temptation. Otherwise, I'm
sure you're going
to have to rebuild the skin a little bit later.
Seven major problems are encountered in
making aircraft skins.
The following
list covers the reason why the machine owner has
to rebuild the skin:
1, inadequate
preparation of the work surface
2, choose
fabric weight error
3. Failure to comply
with the procedures manual
4, the fabric
tension is improper
5. Improper primer
coating
6, inadequate UV protection
7, topcoat problems
Before exploring
these specific issues, there are some
principles to bear in mind. The first is not
to rush to
deliberately slow work. The skin
should be sprayed with several
different
chemicals, each layer must be completely dried,
and
then the next step can be carried out. One
effective experience
is to spray one layer in
the morning, and then spray another
layer in
the afternoon, so that each layer has enough time
to
dry. Another mistake that newcomers often
make is to start with
a large area of skin at
the beginning. Don't give wings or
fuselage
skins up. First of all, start with a small panel,
no
problem, and get a small area of pneumatic
control interview.
In that case, even if it's
screwed up, it doesn't have to be
expensive to
correct mistakes. I also suggest you contact a EAA
studio to learn skinning. Two day weekend
courses can let you
learn some skills
of making skin and the actual operation,
through these training you will have
confidence, dare to make
any aircraft skin
NiuDao.
Another common mistake is the
temperature and humidity problems.
The ideal
working environment of skin fabric, the
temperature
is 77 degrees Fahrenheit, and the
humidity is between 0% and
70%. If the
temperature is below 60 degrees and (or) the
humidity is above 90%, then stop and wait for
the weather to
be better. If nitrocellulose or
butyric acid is used, the
temperature and
humidity requirements must be more stringent.
The temperature should not be lower than 65
degrees Fahrenheit
or the humidity is greater
than 80%. The temperature is high,
but not too
tight. Spraying may be used to reduce the
volatilization rate of additives, used to
adjust and offset
high temperature and
humidity problems. This is a little bit
more
detailed when we talk about colored topcoat.
We solve these problems one by one.
Preparation of skin facing
Newcomers
tend to have the wrong idea, that the fabric paste
on the fuselage, when the skin production
officially started.
Far from it, it takes a
lot of time and energy before cutting
and
laying the fabric. Experienced people know that
it's the
preparation stage that accounts for
most of the work done by
skinning. There are
one or two have to say, if it is for the
old
plane to skin, then to dismantle the old skin
should pay
attention to it, try to keep the
old skin intact observation
board, and
strengthen the control and drainage grommets cable
through holes, thus laying new skin
helps to grasp these parts
position. Secondly,
pay attention to ensure that epoxy primer
is
used for metal and glass fiber, and epoxy varnish
for wood
part. Why? Because most other types
of primers and varnishes
will be removed in
the process. When making use of skin and
butanone reducing agent on epoxy primer and
varnish has no
effect, whereas removal effect
on other types of paint and
varnish, like
paint remover, the accumulation of water vapor
in the paint bubble, no end of trouble for the
future. If other
types of primers and
varnishes are used, then a test is done
before
the skin fabric is laid. Take a piece of cloth
soaked
with butanone and put it on the
workpiece for about 30 minutes,
If the
primer or varnish can be removed, the surface of
the
workpiece needs to be redone. Usually,
epoxy resin can be
sprayed directly on the
original paint, and the old paint does
not
need to be removed. This can also be done first by
spraying
a little bit of epoxy on a small
piece of old paint to make sure
that the epoxy
does not paint off and then use it in a large
area.
When spraying primer or
topcoat, the working surface must be
clean, no
oil, no stains. Do not rust primer, rust first,
and
then the first sealing paint, steel parts
within a few hours
will not seal the paint in
place will rust. Be sure to file all
the burrs
that will be covered by the fabric and do the work
like that. I don't recommend polyester filler,
it will not fill
certain shrinkage cracking,
using epoxy resin, it can be used
for wood,
glass fiber or metal, results are as good as.
Perhaps
a piece of cloth should be filled in a
badly concave place.
Polyester filler is often
used between aluminum (or laminate)
and
cloth itself.
All the sharp edges that
may be worn through the fabric should
be
sealed with anti abrasion tape. This usually
refers to rivet
head, metal seam and sharp
corner. Just watch it. If you don't
think it's
right, seal it with tape. Don't pick the tape that
you paint when you spray paint. It leaves
water, and it gets
into trouble later. Don't
use paper tape. It's Brown for a long
time and
comes out through a light colored topcoat. In the
Mongolian front wing, keep parallel ribs, rib
support belt is
used for this purpose, in this
heat shrinkage skin, ribs will
keep straight.
When the skin is finished, the wing rib brace
looks like a X between the ribs.
Choosing the right cloth weight
Choosing the fabric with the proper weight has
a great influence
on the life of the aircraft
skin. If you use light weight fabric,
there
must be a problem. Let's see what fabric is
available
first. Grade a cotton fabrics were
still used until the 60s of
last century, and
then they were replaced by polyester fibers
with thermal shrinkage properties (polyester).
As far as I know,
a class of cotton fabric is
almost impossible to find now. If
you can find
it again, make sure it complies with the FAA and
do some tests before using it. Maybe you've
got some old cloth
that you can't use. My
suggestion is not to consider a grade
of
cotton fabric, polyester fabric with more
smoothly.
Cotton fabric (Grade A Cotton)
definition:
cotton, in line with the military
standard MIL-C-5646F
requirements. Fabric
tensile strength of not less than 80
pounds per square inch, warp and weft
yarn number is both yarn.
The width of the
fabric is 60 inches.
Polyester fabric has
different specific gravity and tensile
strength, and can be divided into light,
medium and heavy. Light
1.7 ounces per square
yard, used to J-3 the size of the aircraft
skin, all fabric weighs about 9 pounds, medium
weight fabric
2.7 ounces per square yard, all
the weight of fabric to about
14 pounds, 3.4
ounces per square yard of heavy fabric, fabric
weight is about 18 pounds. In general, spray
paint will increase
the weight of 30-40
pounds, depending on the different coating
process. The tensile strength of lightweight
to heavy fabrics
varies from 70 pounds to 130
pounds per square inch. Choosing
the right
fabric for airplanes is also simple. If it's for
ultralight, glider or power less than 65
horsepower aircraft
skin, you can choose
lightweight fabric. If you give a stunt
machine, a biplane, a military aircraft or a
farm machine, in
short, make a skin for those
high wing, bad flying aircraft,
heavy fabric.
Other aircraft (which accounts for most) should
use medium weight fabrics. Heavy fabric can't
be used anywhere.
Trouble is more likely to
happen when you choose fabrics that
are
lighter than recommended values. The surface of
the coating
due to the fabric itself,
aerodynamic flapping tremor movement
damage.
So, if you're not sure, add a few pounds, and use
heavier
fabric.
By the way, polyester
fiber fabric Ceconite, Superflite and
Poly-
Fiber are basically the same, are from the same.
They can
shrink about 10%, and the number of
yarns in the warp and weft
direction is the
same. That is to say,
Don't worry
about the direction of the fabric. It can be laid
in any direction.
Construction
according to operation regulation
That's
a key. You must follow the written instructions of
the
skin fabric manufacturer. As mentioned
earlier, STC
Production aircraft must not
be confused with skinning
procedures. This is
not only related to the legal issues of
Airworthiness of aircraft, but also related to
the possibility
of early repair aircraft skin
repair. For example, Poly-Fiber's
coating
material can not be used with nitrocellulose
lacquer
and butyric acid cloth. If you first
brush the Poly-Brush (the
first paint in the
Poly-Fiber Kit), then paint the
nitrocellulose
lacquer, then the skin will have the trouble of
cracking and peeling. These problems don't
usually happen right
away, wait until you've
done the skin and flown for months, and
then
you're in trouble. What can I do? I'll just have
to hide
it once more.
By the way, if
there is the phenomenon of chapped and peeling
coating, it is not feasible to simply scrape
off the paint, and
the best way to deal with
it is to rebuild the skin. Learn from
other
people's experience and do it according to the
instructions. You don't have to rebuild your
airplane in
fifteen years.
Another
thing to pay attention to is to avoid trying to
challenge mature processes. I've met some
enthusiasts who have
fun doing every process,
from putty to fabric, to latex coated
walls. Let me make it clear, the
business has experimented, and
as far as I
know, they don't do it with home latex paint. In
short, don't do what you don't call in the
construction manual
unless you want to pay a
large amount of tuition fees.
Fabric
tension
How tight should the cloth be
before brushing? It's a problem,
and if it's
bad, it'll cause other problems. Stretched tight
enough there will be trouble, but if too tight
and easy to cause
damage to fabric structure.
Too loose, paint paint may cause
cracks and
flaking due to air beating and shaking. Anyway, be
patient with heat shrink. Remember, the fabric
has about 10%
shrinkage, and you should
remember this when you cover and
stitch the
fabric. Don't be too loose or too tight. There is
a rule of thumb for testing the tension, and
the cloth should
be about 1 inches higher than
the wing before the surface of
the body, such
as the wing, before the heat shrink.
The
heat shrinkage process of the cloth needs an iron.
That's
for sure. Never use an airbrush,
because you can't control the
jet temperature
at all. Heat shrinkable cloth must rely on the
exact temperature of the iron, which is to use
more than 1100
watts of iron power caixing.
The temperature of the iron should
be
carefully adjusted. The error should not exceed 10
degrees
fahrenheit. The fabric will be shrunk
by about 5% at the
temperature of 250. If the
coating is nitro and butyric acid,
then the
temperature is the temperature of the heat shrink
process. The nitro and butyrate coating will
continue to
stretch the fabric for a long time
to come. If it's for a light
or smaller
aircraft to make a skin, consider the structural
factors, use 250 degrees fahrenheit.
When the fabric shrinks,
it will produce great
bending force and twisting force. The use
of
iron should pay more attention to this phenomenon.
Most aircraft require 350 degrees
Fahrenheit as final heat
shrinkable
temperature, which ensures proper fabric tension.
No more than 350 degrees. At 375 degrees, the
fabric starts to
soften, and actually the
fiber structure is relaxed. In this
case, the
fabric doesn't look as tight as it does. At 415
degrees,
the fibers began to melt. Because of
this, the glass thermometer
must be used to
adjust the temperature of the iron. I don't
recommend the spring thermometer, which is
less accurate than
the bubble type. The Poly-
Fiber skin construction manual
details the
method of tuning the temperature of the iron. No
matter what kind of fabric it is, I recommend
buying a
Poly-Fiber skin construction manual
that explains the
placement of the fabric in
detail.