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These systems are used to locate specific wing frames, fuselage
bulkheads, or any other structural member of an aircraft. Several types of
systems are used. Listed below are the numbering systems.
Key points:
Airframe reference data, reference datum line,
aircraft body, fuselage station numbers, body water lines, body buttock lines,
buttock line, wings station numbers, panel numbering, locating access panels,
Cartesian coordinates, reference datum line
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Reference
Datum Line
This is an
imaginary vertical plane located at or near the nose of the aircraft. It is
from this line that all horizontal distances are measured.
Note: Station
numbering are used on large aircraft like transports or tankers:
AIRCRAFT
BODY (FUSELAGE) STATION NUMBERS,
We must have a
starting point when using station numbers. The reference datum line is the
starting point. The reference datum line is near the nose of the aircraft. The
aircraft stations are numbered in inches fore or aft of this line. Most aircraft
components can be located by a station number that specifies the number of
inches the component is located from the reference datum line, as shown in
Figure 1-44. If the component is on the wing the wing station number shows the
number of inches to the right or left of the aircraft centerline that the
component is located.
Figure 1-44,
Fuselage Station Numbers and Water Line Numbers
BODY
WATER LINES,
The reference
for water lines is at some point below the fuselage and is called 0 water line.
Horizontal, parallel lines are then drawn and numbered. The numbers tell how
many inches the lines are from 0 water line.
BODY
BUTTOCK LINES (BUTTOCK LINE),
The body buttock
line is a vertical line is drawn through the center of the fuselage. This line
is called 0 (zero) body buttock line. As illustrated in Figure 1-45, it divides
the fuselage station in half. A series of body buttock lines is then drawn
parallel to the 0 line. They are numbered in the same way as fuselage stations.
A negative number indicates those on the left of the centerline and a positive
number indicates those on the right of the centerline.
Thus, for
components in the main fuselage of the aircraft, these three numbers are
sufficient to exactly define its position in the aircraft. However, if the
component is found along or inside one of the wings, another number is
required. This number is called the wing station (WS) number and is measured
along either wing, beginning at the centerline of the aircraft and moving
outward along the wing. This is also measured in inches.
Figure 1-45, Body
Buttock Lines
WINGS
STATION NUMBERS,
The wings,
nacelle, and tail surfaces are also divided into stations as shown in figure
1-46. Body buttock lines measure horizontal distances at these stations and
vertical distances are measured by water lines.
Figure 1-46,
Wing Station Numbers
Panel
Numbering
LOCATING
ACCESS PANELS,
The best way to
find aircraft components is to first find the access panel or door that will
provide access to the different components. The access panels or doors are
numbered differently on different aircraft. On some aircraft, the access panels
on the left have odd numbers and those on the right side have even numbers. On
other aircraft, the access panels on the right side have an ”R” associated with
the number, while the numbers on the left side have an ”L.” There are other
numbering systems, so you must refer to the –2 TO for the specific aircraft to
find a list of access panels and doors.
Each access door is
numbered and the numbers are listed to show the component to be found behind
each panel or door. See Figure 1-47. Normally, the –2 TO will show which panel
you must open or remove to do a task. Then all you should do is refer to the –2
TO to find out where the panel is located. Not all the components can be found
by locating the access door. Some aircraft parts and components must be found
by the use of aircraft station numbers
Figure 1-47,
Aircraft Panel
CARTESIAN
COORDINATES,
Cartesian
coordinates are used to pinpoint the location and placement of each part on the
airplane, from attachments to major assemblies, using the X, Y, and Z-axis for
planes of reference. See
Figure 1-48.
Landing
gear provides support and directional control of the aircraft while on the
ground, and is a means for the aircraft to transition from the ground to the
air. During landing and taxiing, the gear will provide a cushion effect that
absorbs shock. A landing gear assembly consists of a shock strut, actuating
cylinders, side and drag brace, torque links, and a wheel and brake assembly.
When the landing gear is retracted during flight, drag is reduced. On most aircraft,
the landing gear will be enclosed in an opening either in the nacelle,
fuselage, or wings, and streamlined with doors.
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Points discussed:
Landing gear type and configurations, bicycle landing
gear, modified tricycle landing
gear, quadra-cycle landing gear, shock
strut of landing gear, shock strut shock strut, Trunnion of landing gear, nose
landing gear, torque links of landing gear, steering system of landing gear,
nose wheel steering switch, rudder pedals/steering wheel, centering
cams/motors, type of wheels, wheel markings, torquing instructions, arresting
systems, drag chute,
The
bicycle type landing gear, figure 1-37, consists of a main gear mounted in the
forward fuselage and a second steerable main gear in the aft fuselage.
Outriggers or wing tip protection gears may be provided to support and balance
the aircraft wings during takeoff, landing and ground operations.
Figure
1-37, Bicycle Type Landing Gear
TRICYCLE.
The most common type of landing gear pattern is the tricycle type. Figure 1-38.
This arrangement consists of a nose landing gear and two main landing gears.
The main landing gears are located slightly aft of the center of gravity (the
forward and aft balance point of the aircraft). The distance between the main
landing gears will vary with the size of the fuselage and wings.
Figure
1-38, Tricycle Type Landing Gear
MODIFIED TRICYCLE Landing Gear,
The
C–5 landing gear is a fully retractable modified tricycle type with four main
landing gear shock struts with six wheels mounted on bogie type units that
retract into pods on each side of the aircraft. Figure 1-39. The nose gear is a
four-wheel steerable unit, which retracts aft into the fuselage nose wheel
well.
Figure 1-39, Modified Tricycle Type Landing
Gear
QUADRA-CYCLE LANDING GEAR,
The
quadra-cycle landing gear, Figure 1- 40, is used on the B–52 aircraft. It
consists of four main gears mounted in the fuselage in the form of a rectangle
and two outriggers or wing tip protection gears, as shown. The wing tip
protection gear is located near the outboard end of each wing to provide
lateral stability.
The quadra-cycle landing gear retracts into
the fuselage, which allows the use of a thinner wing design and results in
greater speeds.
Figure
1-40, Quadra-cycle Landing Gear
Aircraft
Shock struts:
SHOCK STRUT of Landing Gear,
The purpose of the shock strut is to absorb
shock during take off, landing, and ground operation. The shock strut is a
pneudraulic unit that consists of several components. Each component serves a
specific purpose. Refer to Figure 1-41 as we discuss each of these components.
OUTER
AND INNER CYLINDER of Landing Gear,
The
inner cylinder or piston is on the lower part of the strut and the axle is at
the lowest point. The inner cylinder slides inside the outer cylinder to give
the desired shock absorbing qualities. This shock strut is serviced with
hydraulic fluid and nitrogen or dry air. A set of seals at the lower part of
the outer cylinder keeps the unit from leaking oil or the air charge.
Figure 1-41, Shock Strut
TRUNNION of Landing Gear,
At the top of the outer cylinder is the
trunnion. Figure 1-42. This is the point at which the landing gear is attached
to the aircraft structure. It is also the pivot point for extending and
retracting the landing gear.
Figure
1-42, Landing Gear Trunnion
Nose landing gear
TORQUE LINKS of Landing Gear,
The torque links are attached at the base of
the outer cylinder and just above the axle on the inner cylinder. The torque
links are hinged in the middle and at their attaching points. This allows the
inner and outer cylinder to telescope. Torque links also keep the inner
cylinder from rotating or spinning.
STEERING SYSTEM of Landing Gear,
Most aircraft have steerable nose wheels. Nose
wheel steering provides a means of directional control when the aircraft is
taxiing, during takeoff and on landing roll. Certain conditions must be present
for nose wheel steering to operate. There must be DC electrical power,
hydraulic pressure, and the ground safety switch must be closed.
NOSE WHEEL STEERING SWITCH,
To energize the nose wheel steering system on
some fighter aircraft, the nose wheel steering switch must be depressed,
opening a solenoid controlled shutoff valve. This switch is located on the
control stick grip. On most heavy type aircraft, the nose wheel steering is
automatically engaged when weight is on the landing gear or when the landing
gear is down and locked.
RUDDER PEDALS/STEERING WHEEL,
On fighter type aircraft the rudder pedals
allow the pilot to select the direction and degree of travel. The rudder pedals
are connected to the nose gear steering system by mechanical linkage and
electrical circuits. These allow the steering power unit/servo valve to control
nose wheel steering.On many large
aircraft, the nose wheel steering system is controlled by a steering wheel
located to the left and forward of the pilot. The steering wheel controls the
direction and degree of travel of the nose wheel. When small amounts of
movement are required for corrections on takeoff and landing, the rudder pedals
will give the pilot up to 8° of steering. This minor amount of steering aids in
high speed ground movement because the normal steering wheel control could
easily over control the aircraft.
CENTERING CAMS/MOTORS,
One
notable difference between main and nose gear shock struts is the centering
device found in nose struts. Two types of centering devices are shown in
Figures 1-43 and 1-44. The upper cam is attached to the top of the piston
(inner cylinder), and the lower cam is connected to the inside bottom of the outer
cylinder. When the weight of the aircraft is removed from the gear, the shock
strut piston extends and forces the upper cam into the lower cam. The seating
of the two cams aligns the wheel for proper retraction into the wheel well.
When the weight of the aircraft is on the gear, the upper cam is unseated from
the lower cam and the wheel is free to swivel.
Figure 1-42, Figure 1-43,
V Type Centering Device Nose Strut,
Centering(Cam and Lobe Type)
Wheels/Tires,
TYPE OF WHEELS,
One
type of aircraft wheel is the split type wheel mostly used on large aircraft.
This type of wheel is in two halves and it is bolted together. When bolted
together both halves must have identical part numbers and manufacturer. The
second type of aircraft wheel used is the split rim (removable flange) wheel;
this is primarily used on fighters. The flange portion of the wheel is held on
with a locking ring, this type of wheel is faster in changing out the rubber
(tire), making it go back into service faster. Aircraft wheels are usually made
of aluminum, magnesium, or steel alloy. These materials are susceptible to
corrosion. To help reduce corrosion and failure, all aircraft wheels will be
cleaned, inspected and repaired. This maintenance will be accomplished at the
time of tire change.
WHEEL MARKINGS,
On
each wheel there are markings very much like those on a tire. Each wheel is
made for a specific type of tire. Each half of a split wheel has a part number
and manufacturer stamped on it. Wheel halves must be matched with respect to
wheel part number and manufacturer when assembled.
•
Size. The wheel size is stamped on each half of the split wheel.
•
Serial Number. Each wheel half has a serial number stamped on it. This number
will be used when turning in the wheel after a wheel and tire change
•
Disassembly Warning. A warning is stamped on the wheel which reads: Deflate
tire before loosening tie bolts. The tie bolts hold the wheel halves together
on a split wheel. If tie bolts are loosened before the tire is deflated, the
wheel and tire may explode.
• Torquing Instructions,
The
tire shop puts the wheel halves together. The bolts must be torqued in a
specific way and to a specific torque. These instructions are stamped on the
wheel.
TIRE
SHOP,
The
tire shop is where the tires and wheels are put together and inflated. A modern
tire shop uses pneumatic tools for disassembly an reassembly of the wheels. The
tire shop will also have vats of solvent for cleaning the used parts. This is
so a through inspection can be made to determine if the part can be reused.
Arresting Systems,
Arresting
gear is usually installed on fighter type aircraft. The arresting gear is made
to stop the aircraft on the runway in case of an emergency. The arresting gear
is located underneath and at the rear of the aircraft. DO NOT walk or crawl
under the arresting gear. This is a very dangerous area and can cause serious
injury or death. Always make sure the arresting gear is safely pinned when the
aircraft is stationary.
DRAG CHUTE,
With
high landing speeds, drag chutes are often installed to assist the aircraft
braking system. These drag chutes allow aircraft to land on shorter runways at
higher speeds and weights.
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The nacelle is what houses or encloses the engine.
This helps to streamline engines during flight. On most heavy aircraft the
engines are located under the wings, therefore they need some form of
streamlining. Most tactical aircraft usually have their engines enclosed in the
fuselage.
Wing
Structural Components,
Wings of an aircraft are designed to produce a lifting
force when moved through the air. The airflow must be directed over and under
the wing to create lift. Due to the curved surface the velocity of the air
moving over the top of the wing is much greater than the air moving along the
bottom of the wing.
Aircraft wing
design depends on a number of factors: size, weight, use of the aircraft,
desired landing speed, and rate of climb. Larger compartments of the wings may
contain fuel tanks. Wings also have flight controls ailerons that are attached
by hinges to the trailing edge to control the roll movement of the aircraft.
Types
of Wing Construction,
There are two basic types of wing construction found
on today’s aircraft, semi cantilever and cantilever.
•
Semi-Cantilever wing,
A semi-cantilever wing is a type of construction that
uses some type of external bracing usually a strut. This strut can be one piece
or it may be of a triangular construction. The strut is usually attached to the
underside of the wing and to a reinforced section of the fuselage. Some
privately owned aircraft use this.
•
Cantilever wing,
Cantilever wing construction is built in such a way
that no external bracing is required. This means the wing is assembled so that
it carries all the weight of the aircraft. The cantilever type construction is
the most commonly used on today’s military aircraft.
STRUCTURAL
MEMBERS.
As we stated earlier, the lifting force applied to the
wings, and the load that is carried inside the wings, require the wing
structure to be very strong. Wings are subjected to stress, such as twisting
and bending. These stresses are resisted by a truss construction of the wing
itself. Aircraft wings have structural members called spars, stringers,
stiffeners and ribs.
SPARS.
Spars are the main structural units of the wing.
They extend from the wing root to the wing tip. They
must have the ability to resist twisting and bending. This is why there is no external
bracing on the full cantilever constructed wing.
Spars are the longest and strongest members of the
wing.
RIBS.
Notice how the ribs are fastened to
the spars and stringers to give cross sectional strength and shape to the wing.
They also transfer the wing load from the covering skin to the spar. To reduce
the weight of a solid rib, lightening holes are punched or cut in areas of low
stress.
Stringers Wing
The stringers may be as long as the spars and are
installed parallel to the spars. They are lighter in weight than the spars.
Stringers are used to add strength to the frame and for attaching the skin. See
figure 1-35, stringers are colored blue for identification.
Stiffeners.
Stiffeners are
used to give more support in critical areas such as between the ribs. Some
stiffeners are made as a part of the rib while others can be removed so work
can be done. Stiffeners are also used to support the skin and other units.
WING SKIN. Wing skin is either aluminum alloy covering
or honeycomb construction. Some aircraft wings may be a combination of both.
The aluminum alloy cover used on the wings is similar to that used on the
fuselage.
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An airplane has six main parts—fuselage, wings,
stabilizer (or tail plane), rudder, one or more engines, and landing gear.
The
fuselage is the main body of the machine, customarily streamlined in form. It
usually contains control equipment, and space for passengers and cargo. The
wings are the main supporting surfaces. Modern airplanes are monoplanes
(airplanes with one wing) and may be high-wing, mid-wing, or low-wing (relative
to the bottom of the fuselage). At the trailing edge of the wings are auxiliary
hinged surfaces known as ailerons that are used to gain longitudinal control
and to turn the airplane.
The lift of an airplane, or the force that supports it
in flight, is basically the result of air moving over the surfaces of the
wings. The lift varies with velocity (airspeed); there is a minimum velocity at
which flight can be maintained. This is known as the stall speed. Because speed
is so important to maintain lift, objects such as fuel tanks and engines, that
are carried outside the fuselage are enclosed in structures called nacelles, or
pods, to reduce air drag (the retarding force of the air as the airplane moves
through it).
Directional stability is provided by the tail fin, a
fixed vertical airfoil at the rear of the plane. The stabilizer, or tail plane,
is a fixed horizontal airfoil at the rear of the airplane used to suppress
undesired pitching motions. To the rear of the stabilizer are usually hinged
the elevators, movable auxiliary surfaces that are used to produce controlled
pitching. The rudder, generally at the rear of the tail fin, is a movable
auxiliary airfoil that gives the craft a yawing (turning about a vertical axis)
movement in normal flight. The rear array of airfoils is called the empennage,
or tail assembly. Some aircraft have additional flaps near the ailerons that
can be lowered during takeoff and landing to augment lift at the cost of
increased drag. On some airplanes hinged controls are replaced or assisted by
spoilers, which are ridges that can be made to project from airfoils.
Airplane engines may be classified as driven by
propeller, jet, turbojet, or rocket. Most engines originally were of the
internal-combustion, piston-operated type, which may be air- or liquid-cooled.
During and after World War II, duct-type and gas-turbine engines became increasingly important, and since then
jet propulsion has become the main form of power in most commercial and
military aircraft. The landing gear is the understructure that supports the
weight of the craft when on the ground or on the water and that reduces the
shock on landing.
The airframe components are constructed from a wide
variety of materials and are joined by rivets, bolts, screw, and welding or
adhesives. The aircraft components are composed of various parts called
structural members. Aircraft structural members are designed to carry a load or
to resist stress. A single member of the structure may be subjected to a
combination of stresses. In most cases the structural members are designed to
carry end loads rather than side loads; that is, to be subjected to tension or
compression rather than bending.
Strength may be the principal requirement in certain
structures, while others need entirely different qualities. For example,
cowling, fairing, and similar parts usually are not required to carry the
stresses imposed by flight or landing loads. However, these parts must have
such properties as neat appearance and streamlined shapes. Every square inch of
a wing and fuselage, every rib, spar and even each metal fitting must be
constructed in relation to the physical characteristics of the metal from which
it is made. Every part of the aircraft must be planned to carry the load
imposed upon it. Although planning the design is not the function of the
mechanic, it is important to understand and appreciate the stresses involved in
order to avoid changes in the original design through improper repairs.
AIRCRAFT
FUSELAGE.
See Figure 1-31. The word fuselage originated during
the early developments in French aviation and is still used to designate the
body portion of an aircraft. The original purpose of the fuselage was to
support the empennage for directional control and stability. Later, the
fuselage was used as a primary structure to which all other components, such as
engines, landing gear, and wings were attached. This is still the primary
function of the fuselage.
The second
purpose of the fuselage is to carry the crew and cargo. The type of
configuration is often determined by the basic mission of the aircraft. The
three types of fuselage construction are the truss, monocoque, and the
semi-monocoque.
Figure 1-31, Major Structural Components of Cargo Type Aircraft
Construction
style:
AIRCRAFT
TRUSS.
See Figure 1-32, in architecture and engineering, a
supporting structure or framework composed of beams, girders, or rods commonly
of steel or wood lying in a single plane. A truss usually takes the form of a
triangle or combination of triangles, since this design ensures the greatest
rigidity. Trusses are used for large spans and heavy loads, especially in
bridges and roofs. Their open construction is lighter than, yet just as strong
as, a beam with a solid web between upper and lower lines. The members are
known as tie-beams, posts, rafters, and struts; the distance over which the
truss extends is called the span. The upper and lower lines or beams are
connected by web members.
Figure
1-32, Fuselage Construction
AIRCRAFT MONOCOQUE CONSTRUCTION.
The monocoque type of fuselage construction is like a
shell in which the skin of the fuselage carries the primary stresses. Rings and
bulkheads are used to shape the fuselage. Since no longitudinal bracing members
are present, the skin must have sufficient thickness and strength to keep the
fuselage rigid. Thus, weight becomes a problem. Most early aircraft featured
this type of construction.
SEMI-MONOCOQUE
CONSTRUCTION.
The semi-monocoque type of construction uses aluminum
alloy and is used in nearly all present-day aircraft. The fuselage members are
arranged so that each member carries part of the load.
Fuselage Structural Components
AIRCRAFT
LONGERONS.
The longerons are the longest and strongest structural
members of the fuselage and are used primarily to obtain strength. They run
from the nose of the fuselage to the empennage. In the total construction the
longerons hold the rings, formers, and bulkheads together. The rings, formers,
and bulkheads hold the stringers.
AIRCRAFT
STRINGERS.
Stringers are small, lightweight members running
lengthwise from the nose of the fuselage to the empennage. Stringers furnish
some strength but are mainly used for attachment of the skin. The skin of the
aircraft is fastened to the stringers by rivets, screws, and other fasteners.
AIRCRAFT
BULKHEADS.
Bulkheads give cross-sectional strength to the
fuselage and divide the aircraft into compartments bulkheads are the strongest
support members, set at a 90° angle to the longitudinal axis. Bulkheads that
separate pressurized compartments have doors with seals to prevent pressure
loss. Bulkheads also have openings for conduits, hoses, lines, and control
cables to pass through.
AIRCRAFT
EMPENNAGE.
The empennage is the stabilizing group of surfaces
located at the aft section of the fuselage, and is designed to balance and
stabilize the aircraft during flight. The empennage has two main parts, the
horizontal stabilizer and the vertical stabilizer.
AIRCRAFT
Horizontal stabilizer.
The horizontal
stabilizer is the horizontal tail surface which keeps the aircraft stable about
the lateral axis. Attached by hinges to its trailing edge are the elevators,
which control the up and down movement, or pitch, of the aircraft. On some
aircraft, the entire surface moves. This type of unit is called a stabilator
and is commonly found on fighter aircraft.
Figure 1-33, Empennage
AIRCRAFT
Vertical Stabilizer.
The vertical stabilizer, figure 1-33, gives the
aircraft positive stability about the vertical axis. The rudder is the hinged
flight control surface attached to the trailing edge of the vertical
stabilizer. It controls the side-to-side movement, or yaw, of the aircraft
(fishtailing effect).
This is an Aerospace engineering concerned with the development of aircraft and spacecraft, focused on designing aeroplane and space shutlle and it is a study of all the flying wing used within the earth's atmosphere. Also dealing with the Avionic systems that includes communications, navigation, the display and management of multiple systems. Also dealing with Aircraft mishap such as Accident and Serious Incident
