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8. Down, due to gyroscopic effect.
9. The blade angle of attack is more
efficient.
Airframes, Engines &
Systems
The airframe is the complete structure
of an aircraft, without engines and
instruments. It will be as light and as
strong as possible, because many
forces are encountered in flight, like
compression, tension, torsion, shearing and
bending, so materials such as wood,
aluminium, titanium, fabric and
carbon fibre are used (aluminium is
too soft by itself, so it will be mixed
with copper, manganese or
magnesium for strength). Instead of
being solid, where bulk is needed, a
honeycomb construction will keep things
light. This is a framework made of
short hexagonal tubes covered over
both open ends by metal sheeting.
The fuselage is where the pilot,
passengers and cargo are placed, and
to which any wings, tailplanes,
tailbooms and main rotors are
attached. Older aircraft will be made
of a truss construction, or frame and skin,
where aluminium or steel tubing is
joined in a series of triangular shapes
(like the tail boom of the Bell 47
helicopter), then covered with metal
or fabric (in this case, the metal acts
merely as a cover, making no
contribution towards strength). One
disadvantage is that cross bracing
takes up a lot of space.
More modern machines use
monocoque, which is a development of
stressed skin, where the outside
covering itself is rigid and takes the
stresses of flight, and supporting
devices inside, like formers held
together by stringers, or longerons,
provide the shaping (this is also a
typical method used on the tail
booms of most modern helicopters).
Formers give the fuselage its basic
shape, and are assembled one after
the other, changing in size as
required. They will absorb torsion and
bending loads. Longerons run fore and
aft, keeping the formers together,
spreading the load between them
and stiffening the structure in
general. Bulkheads are similar to
182 Canadian Professional Pilot Studies
formers, but tend to be found at
both ends of the fuselage, at each
end of a compartment, or when
more strength is required.
A firewall is a fireproof partition that
separates the engine compartment
from the cabin. It is normally made
of stainless steel.
In a wing, ribs are the equivalent of
formers, and they are held in place
with spars, which perform a similar
function to longerons. Modern
wings will also contain fuel tanks,
which may or may not contribute to
the strength of the wing.
An egg is a good example of a
monocoque structure, which is
handy, as cocque is French for eggshell.
Aside from saving weight, the big
advantage of monocoque is that it
leaves more space inside the aircraft.
Older flying boats, made of wood,
were among the earliest examples.
Aeroplanes
Aeroplanes are either low wing, like
most Piper aircraft (see overleaf), or
high wing, like the average Cessna:
High wing planes may have struts to
help keep the wings up, as well as
internal bracing. Both types are also
called cantilever, or semi-cantilever,
respectively.
Aeroplanes are single- or multi-engined,
with fixed or retractable
undercarriages, if they are
landplanes, skis if they land on snow,
and floats if they operate on water:
A monoplane has one pair of wings,
while a biplane has two (the Red
Baron's triplane had three. I forget
what Snoopy had). The shape of a
wing as viewed from above is known
as a planform, and could be rectangular,
tapered (from root to tip), elliptical,
delta or sweptback. Large, wide ones,
for example, are good for large
transport aircraft, and short, stubby
ones will be found on fast sports
aircraft. The aspect ratio of a wing is
the relationship between its length
and width, or span and chord. You
could have two wings of equal
surface area but different aspect
ratios, depending on what they were
designed for. The higher the ratio
(i.e. the longer the wing relative to its
width), the more lift you get, with
less induced drag and downwash (as
with gliders):
However, it does stall at a lower
angle.
Airframes, Engines & Systems 183
An aeroplane's rated strength is a
measure of the load the wings can
carry without being damaged. Light
aircraft can take total loads in three
categories:
· Normal, 3.8 x the gross weight
· Utility, 4.4 x gross weight
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