AIRCRAFT BASIC CONSTRUCTION
INTRODUCTION :
Naval aircraft are built to meet certain specified
requirements. These requirements must be selected so
they can be built into one aircraft. It is not possible for
one aircraft to possess all characteristics; just as it isn't
possible for an aircraft to have the comfort of a
passenger transport and the maneuverability of a
fighter. The type and class of the aircraft determine how
strong it must be built.
A Navy fighter must be fast,
maneuverable, and equipped for attack and defense. To
meet these requirements, the aircraft is highly powered
and has a very strong structure.
The airframe of a fixed-wing aircraft consists of the
following five major units:
1. Fuselage
2. Wings
3. Stabilizers
4. Flight controls surfaces
5. Landing gear
A rotary-wing aircraft consists of the following
four major units:
1. Fuselage
2. Landing gear
3. Main rotor assembly
4. Tail rotor assembly
You need to be familiar with the terms used for
aircraft construction to work in an aviation rating.
STRUCTURAL STRESS
LEARNING OBJECTIVE:
Identify the five
basic stresses acting on an aircraft.
The primary factors to consider in aircraft
structures are strength, weight, and reliability. These
factors determine the requirements to be met by any
material used to construct or repair the aircraft.
Airframes must be strong and light in weight. An
aircraft built so heavy that it couldn't support more than
a few hundred pounds of additional weight would be useless. All materials used to construct an aircraft must
be reliable. Reliability minimizes the possibility of
dangerous and unexpected failures.
Many forces and structural stresses act on an
aircraft when it is flying and when it is static. When it is
static, the force of gravity produces weight, which is
supported by the landing gear. The landing gear absorbs
the forces imposed on the aircraft by takeoffs and
landings.
During flight, any maneuver that causes
acceleration or deceleration increases the forces and
stresses on the wings and fuselage.
Stresses on the wings, fuselage, and landing gear of
aircraft are tension, compression, shear, bending, and
torsion. These stresses are absorbed by each component
of the wing structure and transmitted to the fuselage
structure. The empennage (tail section) absorbs the
same stresses and transmits them to the fuselage. These
stresses are known as loads, and the study of loads is
called a stress analysis. Stresses are analyzed and
considered when an aircraft is designed.
METALLIC MATERIALS:
The most common metals used in aircraft
construction are aluminum, magnesium, titanium,
steel, and their alloys.
1/ Alloys:
An alloy is composed of two or more metals. The
metal present in the alloy in the largest amount is called
the base metal. All other metals added to the base metal
are called alloying elements. Adding the alloying
elements may result in a change in the properties of the
base metal. For example, pure aluminum is relatively
soft and weak. However, adding small amounts or
copper, manganese, and magnesium will increase
aluminum's strength many times. Heat treatment can
increase or decrease an alloy's strength and hardness.
Alloys are important to the aircraft industry. They
provide materials with properties that pure metals do
not possess.
2/ Aluminum:
Aluminum alloys are widely used in modern
aircraft construction. Aluminum alloys are valuable
because they have a high strength-to-weight ratio.
Aluminum alloys are corrosion resistant and
comparatively easy to fabricate. The outstanding
characteristic of aluminum is its lightweight.
3/ Magnesium :
Magnesium is the world's lightest structural metal.
It is a silvery-white material that weighs two-thirds as
much as aluminum. Magnesium is used to make
helicopters. Magnesium's low resistance to corrosion
has limited its use in conventional aircraft.
4/ Titanium :
Titanium is a lightweight, strong, corrosionresistant
metal. Recent developments make titanium
ideal for applications where aluminum alloys are too
weak and stainless steel is too heavy. Additionally,
titanium is unaffected by long exposure to seawater and
marine atmosphere.
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