完美生活许巍飞机蒙布工艺(Aircraft fabric process)

2020年12月30日发(作者：华清)
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.