Multiplex Alpina 4001 ELEKTRO Notice De Construction page 25

Appendix
1. Tissue covering, followed by a painted finish; this
method of finishing requires thorough initial sealing of all
wooden surfaces using standard sanding sealer, with
fine sanding between coats. The tissue is applied using
the sealer or clear shrinking dope. Lay the tissue on the
surface dry and apply sealer or dope through it to stick it
to the prepared surface. Be careful to avoid bubbles and
creases. Several more coats of sanding sealer and fine
sanding eventually form a good surface for a painted
finish. On no account apply the coloured paint directly to the
prepared or (even worse) bare wood surface. Apply several
brushed or sprayed coats of colour paint, with fine sanding
(wet-and-dry paper, used wet) between coats. A final light
coat will produce a glossy finish which can then be
polished to give an efficient high-gloss surface. However,
bear in mind that this method is extremely labour-intensive,
and unfortunately the finish is quite easily damaged.
2.) The technique of applying a finish using glass cloth
and resin is described in full detail in our "Resin Primer"
book, Order No. 60 2768, which includes many practical
tips. We strongly recommend that you study this book,
which also provides much valuable information on other
areas of modelling where the modern material of glassfibre-
reinforced plastic (GRP) is beneficial.
3.) Covering with heat-shrink film is the quickest and most
effective finishing method, and gives outstanding results
in terms of appearance, practicality and durability. Just
follow the instructions supplied with the film. Learning
how to apply film is not difficult; provided that you follow the
possible to use the film itself as a hinge. The result can
be every bit as good as a tape hinge. This is only possible
if you have followed the instructions to the letter and
produced really sharp, perfectly straight mating edges on
the wing and the control surface. The top and bottom film
must weld together along the pivot line, and this is only
possible if the edges are really sharp.
The first step is to cover the underside of the wing in the
usual way. Apply film to the control surface as well, but do
not finish the job; simply tack down the edges, trim the film
to size, and iron the edges down (i.e. do not use the heat-
gun). Leave excess film at the ends and especially at the
front (at least 5 cm). Pull the excess round the ends, iron
it down and trim it off neatly. You now have a control surface
sitting on the bench, underside film-covered, not yet shrunk,
and with a wide excess of film running along the whole
length of the leading edge.
Place the wing on the bench resting on its leading edge,
top surface facing you; support it in this position. Lay the
projecting film on the wing recess sealing strip and pull it
tight, so that the flaperon hangs down, resting on the top
surface of the wing. Centre the control surface in the
recess and spot-fix the film in place using the tip of the iron.
Set the aileron to neutral (centre) and check the end gaps
instructions to the letter even your first wing will be a
complete success.
Important:
When covering with iron-on film it is essential to ensure
that the foam core is not overheated, as this can result in
damage (distortion). Some films require a high processing
temperature, and if you are using these types of film you
must take particular care when applying the material. The
guarantee does not cover damage to the flying surfaces
caused in this way.
Some practical tips on film covering
The usual method of applying film is to tack the edges in
place, trim the film to shape, iron the edges down firmly,
then heat the film with a heat gun to shrink it, and rub it down
onto the wood with a soft cloth. This method is effective, but
does have one drawback. No matter how carefully you
sand the surface and remove every trace of dust, you
cannot remove the wood's natural grain texture. When you
rub the warm film down with a soft cloth, the material is
pressed into the surface texture, and inevitably follows the
microscopic ridges and grooves of the wood. The result
is a less smooth surface than you might have expected.
This effect can be eliminated in the following way: instead
of the soft cloth, take a thick piece of balsa - similar to a
sanding block - and stretch a piece of stiff fabric over it as
follows: place the block on the fabric, pull the sides up, and
staple the material down on the top of the block. If you now
rub the film down with the smooth side of this block (your
hand will be a comfortable distance from the heat gun) the
film will not follow the tiny grooves in the wood, and you will
usually achieve a highly efficient super-smooth surface,
approaching that of a moulded GRP wing panel.
The ailerons and camber-changing flaps are usually
attached to the wings using hinge tape. However, it is
in the wing recess. You may find that several attempts are
necessary to obtain identical end gaps. Pull the film taut
so that the aileron is pulled into the correct position against
the wing, and iron the film into place. Cut off the excess film
and iron the edge down permanently. If the control surface
is now brought to the neutral position it should be possible
to see a narrow strip of film between wing and control
surface from above. Fold the control surface onto the top
of the wing again and shrink the film on the underside of
the control surface. This protects the underside of the wing
from heat. Cover the top surface of the wing in the usual
way. Trim the film and iron down the cut edges. Iron the film
down firmly on both sides of the hinge line, then cut through
the film on both sides of the gap from the underside, using
a very sharp knife. The control surface will now be free to
move again. Now comes the most important step: iron
down the film 5 mm from the pivot line on the wing and the
control surface, holding the control surface in the extreme
"down" position. After this run the iron over the whole of the
pivot line to weld the bottom film to the top film. Fold the
control surface right up and back, and repeat the process
on the underside.
When finishing the job with the heat gun, take a little care
when working close to the control surface to avoid loosening
the film hinge. If it does come loose you will need to repeat
the last stage. When you are finished, the control surface
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