A diagram of the fuselage components.
Balsa builders’ parlance
by Paul Kohlmann
This article is the second in a series intended to introduce new builders to the basics of constructing balsa-framed aircraft. In the March
2015 issue, we learned about filling a toolbox with a
basic set of tools.
This month’s topic may seem odd, but it will introduce
new builders to some vocabulary used in the aircraft
industry. Not surprisingly, the terms used to describe
full-scale components are the same that are used for
our smaller versions. After all, full-scale aircraft often
start out as models, just as aeronautical engineers often
start out as modelers.
It is easier to share information when speaking a
common dialect. The purpose of this article is to help
new modelers be able to comprehensively discuss
problems and ideas with other aeromodelers. After
introducing the terminology, this language will be
applied to describe several classic model design styles.
The goal of this article is to
define the components that form
the model’s airframe, but the word
fuselage could use some attention.
It is derived from the French word
fuselé, which means tapered.
As for the components that
make up the fuselage, much of
the terminology was derived from
boat building. This shouldn’t be
surprising because the dawn of
aviation occurred when wooden
shipbuilding was at its peak. I’ll
start with the longitudinal fuselage
components that run from stem to
Keel: Often a fuselage is started by
pinning a keel to the building board.
Keels run the length of the fuselage,
but may be broken by the cockpit or
other openings. Keels are typically the
stoutest structural members running
lengthwise in the fuselage.
Longeron: Similar to keels, longerons
span the length of the fuselage. They
are normally square stock and lighter
than keels. Many lightweight designs
eliminate keels and instead rely on a
framework of four longerons.
Stringer : The lightest longitudinal
element of the group, stringer and
longeron are used interchangeably in
both modeling and aerospace. As a rule
of thumb, stringers are lighter, are often
interrupted instead of running the full
length of the fuselage, and are packed
together tighter than the heavier
longerons. Stringers may also be found
in the wing.
The purpose of keels, longerons, and
stringers is to transfer loads on the
aircraft’s skin to latitudinal elements
such as bulkheads and formers.
Bulkhead: A firewall is a good
example of a bulkhead. In addition
to adding shape to the fuselage, it is a
robust element that adds significant
structure to the airframe. A bulkhead
is often solid and may perform an
additional function such as providing a
mounting location for a motor mount,
landing gear, or a wing pin.
Former : Essentially a bulkhead with
its center removed, a former helps
shape the fuselage but has less strength.
Sheeting : A panel of thin balsa that
forms the airframe’s skin, sheeting may
be used on the fuselage, the wing, or
even the tail parts.
Saddle: The pocket where the
wing attaches to the fuselage may
require additional structural elements,
particularly in the case of low-wing
47 Model Aviation APRIL 2015 www.ModelAviation.com