Figure 1-4.Wing construction.
assembly or power plant with the engine and its
accessories. Vibrations originating in the engine are
transmitted to the aircraft structure through the engine
In single-engine aircraft, the power plant is mounted
in the center of the fuselage. On multiengined aircraft,
nacelles are usually used to mount the power plants. The
nacelle is primarily a unit that houses the engine.
Nacelles are similar in shape and design for the same
size aircraft. They vary with the size of the aircraft.
Larger aircraft require less fairing, and therefore smaller
nacelles. The structural design of a nacelle is similar to
that of the fuselage. In certain cases the nacelle is
designed to transmit engine loads and stresses to the
wings through the engine mounts.
The wings of an aircraft are designed to develop lift
when they are moved through the air. The particular
wing design depends upon many factors for example,
size, weight, use of the aircraft, desired landing speed,
and desired rate of climb. In some aircraft, the larger
compartments of the wings are used as fuel tanks. The
wings are designated as right and left, corresponding to
the right- and left-hand sides of a pilot seated in the
The wing structures of most naval aircraft are of an
all-metal construction, usually of the cantilever design;
that is, no external bracing is required. Usually wings
are of the stress-skin type. This means that the skin is
part of the basic wing structure and carries part of the
loads and stresses. The internal structure is made of
spars and stringers running spanwise, and ribs and
formers running coordwise (leading edge to trailing
edge). The spars are the main structural members of the
wing, and are often referred to as beams.
One method of wing construction is shown in figure
1-4. In this illustration, two main spars are used with ribs
placed at frequent intervals between the spars to develop
the wing contour. This is called two-spar construction.
Other variations of wing construction include
"monospar (open spar), multispar (three or more spars),
and box beam. In the box beam construction, the
stringers and sparlike sections are joined together in a
box-shaped beam. Then the remainder of the wing is
constructed around the box.
The skin is attached to all the structural members
and carries part of the wing loads and stresses. During
flight, the loads imposed on the wing structure act
primarily on the skin. From the skin, the loads are
transmitted to the ribs and then to the spars. The spars
support all distributed loads as well concentrated
weights, such as a fuselage, landing gear, and nacelle.
Corrugated sheet aluminum alloy is often used as a
subcovering for wing structures. The Lockheed P-3
Orion wing is an example of this type of construction.
Inspection and access panels are usually provided
on the lower surface of a wing. Drain holes are also
placed in the lower surfaces. Walkways are provided on
the areas of the wing where personnel should walk or
step. The substructure is stiffened or reinforced in the
vicinity of the walkways to take such loads. Walkways
are usually covered with a nonskid surface. Some
aircraft have no built-in walkways. In these cases
removable mats or covers are used to protect the wing
surface. On some aircraft, jacking points are provided