Balsa Facts (part 2)
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Continued from
Page 1
Balsa Grain — Learn How to Identify All Three Grain Types
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In selecting balsa sheets for use in
your model, it is important to consider the way the grain runs through the sheet
as well as the weight of the sheet. The grain direction actually controls the
rigidity or flexibility of a balsa sheet more than the density does. For
example, if the sheet is cut from the log so that the tree's annular rings run
across the thickness of the sheet (A-grain, tangent cut), then the sheet will be
fairly flexible edge to edge. In fact, after soaking in water some tangent cut
sheets can be completely rolled into a tube shape without splitting. If on the
other hand the sheet is cut with the annular rings running through the thickness
of the sheet (C-grain, quarter grain), the sheet will be very rigid edge to edge
and cannot be bent without splitting. When the grain direction is less clearly
defined (B-grain, random cut), the sheet will have most intermediate properties
between A and C grain. Naturally, B-grain is the most common and is suitable for
most jobs. The point to bear in mind is that whenever you come across pure
A-grain or C-grain sheets, learn where to use them to take best advantage of
their special characteristics.
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A-GRAIN sheet balsa has
long fibers that show up as long grain lines. It is very flexible across the
sheet and bends around curves easily. Also warps easily. Sometimes called
"tangent cut." DO use for sheet covering rounded fuselages and wing leading
edges, planking fuselages, forming tubes, strong flexible spars, HL glider
fuselages. DON'T use for sheet balsa wings or tail surfaces, flat fuselage
sides, ribs, or formers.
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B-GRAIN sheet balsa has
some of the qualities of both type A and type C. Grain lines are shorter than
type A, and it feels stiffer across the sheet. It is a general puropse sheet and
can be used for many jobs. Sometimes called "random cut." DO use for flat
fuselage sides, trailing edges, wing ribs, formers, planking gradual curves,
wing leading edge sheeting. DON'T use where type A or type C will do a
significantly better job.
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C-GRAIN sheet balsa has a
beautiful mottled appearance. It is very stiff across the sheet and spits
easily. But when used properly, it helps to build the lightest, strongest
models. Most warp resistant type. Sometimes called "quarter grain." DO use for
sheet balsa wings and tails, flat fuselage sides, wing ribs, formers, trailing
edges. Best type for HL glider wings and tails. DON'T use for curved planking,
rounded fuselages, round tubes, HL glider fuselages, or wing spars.