Carved Fuselages For Dummies
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A “newbies” guide to building
models from foam or balsa blocks
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by
Johan Wallin
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Introduction
Many times it’s impossible to find stick and
tissue plans of the more odd, but nevertheless interesting
aircraft. Since I’m not too good when it comes
to traditional stick and tissue building, and fond
of less known aircraft I started doing them out
of foam and balsa blocks. There are some excellent
models built using these materials by for example
Dave Deadman, Richard Crossley and Peter Smart,
and they summarised their methods in a series of
articles and a booklet. If you want to see how the
”pros” do it I recommend trying to get
hold of those.
I recently got hold of Deadman et al.’s work
“Foam scale models”,
through the help of kind SFA members. I was surprised
to see that these foam-gurus methods are in most
aspects identical to my own, developed by using
pointers from sources such as the French magazine
MRA as well as lots of trial and error. Much can
also be learnt from the solid fuselage carving “how
tos” found on Ken
Horne’s homepage.
In this version I have included some methods described
in “Foam Scale Models”
that I haven’t used but think may be good.
My models wouldn’t win any competitions, but
the process of carving might be of some interest
nevertheless. This little guide is a description
of how I do it and you will probably come up with
your own, better ways. Just try it!
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Three different materials that can be used when
carving light fuselages for flying models. From
left to right: balsa, blue extruded polystyrene,
and white expanded polystyrene.
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Description of materials and tools
Foam plastics
I’ve used blue extruded polystyrene (PS) such
as ”Floor Mate” and
“Eco prim” as well
as expanded white PS (the beady stuff). There are
other variants of foam PS and polypropylenes (PP),
some heavier, some lighter, but the methods here
described should work with those as well. The foam
can be bought in sheets of about 5 to 12 cm thickness
or you could probably get scraps wherever there
is a house built if you ask nicely. The material
is soft, easily dented, and melts at rather low
temperatures.
The extruded PS foam has small closed cells of air
and it is possible to obtain a rather decent surface
after sanding. In thin sheets, this material goes
under brand names such as Depron.
The expanded PS is lighter than the blue foam and
has a beady structure. This structure makes it harder
to sand to a smooth surface, and it rips more easily
when sanding or cutting. If you have contacts in
a biological lab, you can get an endless supply
of PS boxes for frozen goods, which have a small
bead structure that is excellent for our purposes.
Expanded PP plastic is more resilient and “bouncy”.
Thus, it withstands impact better than expanded
PS, but it’s heavier and perhaps not as easy
to come by.
The tough skin resulting from hot wire cutting makes
the foam heavier than the same thickness without
skin. As it adds considerably to the strength, you
can chose to sand it off or keep it, depending on
which is more important in the application in which
you use it.
Balsa
Our beloved balsa needs no introduction! Choose
light wood. My pistachio balsa fuselages weigh between
1 and 1.5 grams finished which is heavy as pistachios
come, so the lighter the better. The fibre direction
in the block should be from tail to nose on the
finished fuselage.
Tools
You need a sharp knife with a reasonable length.
I use a 1 cm wide, 6 cm long ”snap”
knife and razor blades. The blade has to be kept
really sharp, as it otherwise will tear instead
of cut the plastic. The blade should also be quite
stiff. Dave Deadman instead suggests using hack
saw blades for cutting out the general shape.
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A simple hot wire rig.
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A hotwire cutter is useful, but not necessary. Mine
is a 25 cm NiCr wire with a spring at the top end
to keep the wire taught even when it expands from
heating. It’s mounted vertically and works
like a band saw. I prefer to cut using low temperatures
(i.e. not a glowing wire) so that I can use cardboard
templates and gain some extra ”ooops!-fumbling-time”.
The downside is that I have to cut very slowly to
avoid bending the wire, which would result in a
deformed cut. The fumes are noxious, so keep a window
open or avoid breathing.
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An assortment of useful tools. Sandpaper glued
to sticks of different shapes and sizes can easily
be made to suit the need. The hollowing out tool
(top right) is just a razorblade bent to a loop,
wrapped with card or thin aluminium sheet and
stuck with cellotape to a handle.
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To hollow out the fuselages I use a thin razor blade
from a disposable razor, stuck in a loop to a handle.
The blade is a bit brittle, but I try to make the
loop similar to the final cross section of the hollowed
out space. These blades usually last one fuselage
and then have to be exchanged.
Wet and dry sandpaper of 150, 240, 400, 800 and
the finest grit you can find, are excellent for
shaping and finishing.
Glue
White wood glue (vinyl) works, but I prefer the
yellow aliphatic glues on both foam and balsa. Odourless
cyano, epoxies, UHU por and others
work as well, but not glues with acetone based solvents.
Be sure to try before you use your favourite brand.
Fast tack and easy sanding are the two most important
factors to me.
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How I do it
Step one
Find the 3-view you want to use and scale it. I
use Photoshop, but Corel
Draw or even Word will
do the job quickly or you could just scale it using
a photocopy machine. Make sure the 3-view is symmetrical
where it’s supposed to and that the different
views are of similar scale (length). I usually scale
the wings to a slightly wider chord wise to allow
for the airfoil curvature (see “Wings and
things” below).
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The three-view glued to card and then cut.
On this model I tried to incorporate the
headrest in the template. Bad idea…
It proved easier to make it as a separate
item. |
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Headrests and other small protruding parts
on the fuselage are often easier to add on
later, and should be omitted from the template.
Also remember to allow for a balsa nose block
and front former in the template if you are
using foam. Glue the parts to thick card or
similar and cut them out with a small (1 mm
or so) margin on all sides, to allow for some
sanding in rough fuselage later.
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