| Airplanes Essay, Research Paper
One of the first things that is likely to be noticed
during a visit to the local airport is the wide variety of
airplane styles and designs. Although, at first glance, it
may be seen that airplanes look quite different from one
another, in the long run their major components are quite
similar. These similarities lie in the fuselage, wing,
empennage, landing gear, and powerplant. The four forces of
flight which all planes have in common are lift, weight,
thrust, and drag.
The fuselage serves several functions. Besides being a
common attachment point for the other major components, it
houses the cabin, or cockpit, which contains seats for the
occupants and the controls for the airplane. The fuselage
usually has a small baggage compartment and may include
additional seats for passengers.
When air flows around the wings of an airplane, it
generates a force called “lift” that helps the airplane fly.
Wings are contoured to take maximum advantage of this force.
Wings may be attached at the top, middle, or lower portion of
the fuselage. These designs are referred to as high-, mid-,
and low-wing, respectively. The number of wings can also
vary. Airplanes with a single set of wings are referred to
as monoplanes, while those with two sets are called biplanes.
To help fly the airplane, the wings have two types of
control surfaces attached to the rear, or trailing, edges.
They are referred to as ailerons and flaps. Ailerons extend
from about the midpoint of each wing outward to the tip.
They move in opposite directions – when one aileron goes up,
the other goes down. Flaps extend outward from the fuselage
to the midpoint of each wing. They always move in the same
direction. If one flap is down, the other one is also down.
The empennage consists of the vertical stabilizer, or
fin, and the horizontal stabilizer. These two surfaces are
stationary and act like the feathers on an arrow to steady
the airplane and help maintain a straight path through the
air.
The rudder is attached to the back of the vertical
stabilizer. Used to move the airplane’s nose left and right.
Actually, using the rudder and ailerons in combination during
flight to initiate a turn.
The elevator is attached to the back of the horizontal
stabilizer. During flight it is used to move the nose up and
down to direct the airplane to the desired altitude, or
height.
Most airplanes have a small, hinged section at the back
of the elevator called a trim tab. Its purpose is to relieve
the pressure it must be held on the control wheel to keep the
nose in the desired position. In most small airplanes, the
trim tab is controlled with a wheel or a crank in the
cockpit.
Some empennage designs vary from the type of horizontal
stabilizer. They have a one-piece horizontal stabilizer that
pivots up and down from a central hinge point. This type of
design, called a stabilator, requires no elevator. Move the
stabilator using the control wheel, just as in an elevator.
When you pull back, the nose moves up; when you push forward,
the nose moves down. An antiservo tab is mounted at the back
of the stabilator, to provide a control “feel” similar to
what you experience with an elevator. Without the antiservo
tab, control forces from the stabilator would be so light
that it might might be “over controlled” the airplane or move
the control wheel too far to obtain the desired result. The
antiservo tab also functions as a trim tab.
The landing gear absorbs landing loads and supports the
airplane on the ground. It typically is made up of three
wheels. The two main wheels are located on either side of
the fuselage. The third may be positioned either at the nose
or at the tail. If it is located at the tail, it is called a
tailwheel. In this case, the airplane is said to have
conventional landing gear.
Conventional gear is common on older airplanes, as well
as on some newer ones. It is desirable for operations on
unimproved fields, because of the added clearance amid the
propeller and the ground. However, airplanes with this type
of gear are more difficult to handle during ground
operations.
When the third wheel is located on the nose, it is
called a nosewheel. This design is referred to as tricycle
gear. An airplane with this type of gear has a steerable
nosewheel, which you control through use of the rudder
pedals.
Landing gear can also be classified as either fixed or
retractable. Fixed gear always remains extended, while
retractable gear can be stowed for flight to reduce air
resistance and increase airplane performance.
Just as shock absorbers are needed on a car, some shock
absorbing device is needed on the landing gear. Shock struts
are designed for this purpose. They absorb bumps and jolts,
as well as the downward force of landing.
Airplane brakes operate on the same principles as
automobile brakes, but they do have a few significant
differences. For example, airplane brakes usually are
located on the main wheels, and are applied by separate
pedals. Because of this, operating the brake on the left
independently of the brake on the right, or vice versa is
possible. This capability is referred to as differential
braking. It is important during ground operations when you
need to supplement nosewheel steering by applying the brakes
on the side toward the direction of turn. In fact,
differential braking is extremely important on conventional
gear airplanes, since some do not have a steerable wheel.
In small airplanes, the powerplant includes both the
engine and the propeller. The primary function of the engine
is to provide the power to turn the propeller. It also
generates electrical power, provides a vacuum source for some
flight instruments, and, in most single-engine airplanes,
provides a source of heat for the pilot and passengers. A
firewall is located between the engine compartment and the
cockpit to protect the occupants. The firewall also serves
as a mounting point for the engine.
During flight, the four forces acting on the airplane
are lift, weight, thrust, and drag. Lift is the upward force
created by the effect of airflow as it passes over and under
the wings. It supports the airplane in flight. Weight
opposes lift. It is caused by the downward pull of gravity.
Thrust is the forward force which propels the airplane
through the air. It varies with the amount of engine power
being used. Opposing thrust is drag, which is a backward, or
retarding, force that limits the speed of the airplane.
Lift is the key aerodynamic force. It is the force that
opposes weight. In straight-and-level, unaccelerated flight,
when weight and lift are equal, an airplane is in a state of
equilibrium. If the other aerodynamic factors remain
constant, that airplane neither gains nor loses altitude.
When an airplane is stationary on the ramp, it is also
in equilibrium, but the aerodynamic forces are not a factor.
In calm wind conditions, the atmosphere exerts equal pressure
on the upper and lower surfaces of the wing. Movement of air
about the airplane, particularly the wing, is necessary
before the aerodynamic force of lift becomes effective.
During flight, however, pressures on the upper and lower
surfaces of the wing are not the same. Although several
factors contribute to this difference, the shape of the wing
is the principal one. The wing is designed to divide the
airflow into areas of high pressure below the wing and areas
of comparatively lower pressure above the wing. This
pressure differential, which is created by movement of air
about the wing, is the primary source of lift.
The weight of the airplane is not a constant. It varies
with the equipment installed, passengers, cargo, and fuel
load. During the course of a flight, the total weight of the
airplane decreases as fuel is consumed. Additional weight
reduction may also occur during some specialized flight
activities, such as crop dusting, fire fighting, or sky
diving flights. In contrast, the direction in which the
force of weight acts is constant. It always acts straight
down toward the center of the earth.
Thrust is the forward-acting force which opposes drag
and propels the airplane. In most airplanes, this force is
provided when the engine turns the propeller. Each propeller
blade is cambered like the airfoil shape of a wing. This
shape, plus the angle of attack of the blades, produces
reduced pressure in front of the propeller and increased
pressure behind it. As is the case with the wing, this
produces a reaction force in the direction of the lesser
pressure. This is how a propeller produces thrust, the force
which moves the airplane forward.
To increase thrust by using the throttle to increase
power, thrust exceeds drag, causing the airplane to
accelerate. This acceleration, however, is accompanied by a
corresponding increase in drag. The airplane continues to
accelerate only while the force of thrust exceeds the force
of drag. When drag again equals thrust, the airplane ceases
to accelerate and maintains a constant airspeed. However,
the new airspeed is higher than the previous one.
When the thrust is reduced thrust, the force of drag
causes the airplane to decelerate. But as the airplane
slows, drag diminishes. When drag has decreased enough to
equal thrust, the airplane no longer decelerates. Once
again, it maintains a constant airspeed. Now, however, it is
slower than the one previously flown.
As it has been seen, drag is associated with lift. It
is caused by any aircraft surface that deflects or interferes
with the smooth airflow around the airplane. A highly
cambered, large surface area wing creates more drag (and
lift) than a small, moderately cambered wing. If the
airspeed is increased, or angle of attack, the drag and lift
increases. Drag acts in opposition to the direction of
flight, opposes the forward-acting force of thrust, and
limits the forward speed of the airplane. Drag is broadly
classified as either parasite or induced.
In conclusion, the basic construction of planes are
really quite similar and all planes need the four forces of
flight so that they are able to fly. These things are quite
unique in their own way but without these things the planes
would never be able to fly or even be built.
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