Knox Model Airplane Club 
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Basic Aviation In ancient times there was
little hope of man taking to the air. Ancient man had to make due with fables of manned
flight such as that of Daedalus and his ill fated son Icarus. During the middle ages there
are numerous accounts of man attempting to fly. These efforts, usually a launch from a
tower in a kite-like crude glider, frequently ended with tragic results. The lack of
understanding of aerodynamics and structure usually resulted in the collapse of the
structure and the death of the would-be pilot. Eventually man grasped the
principals of the forces acting upon a flying machine. The first recorded evidence of this
was an engraving made on a silver disk by Sir George Cayley in 1799. On the front of the
disk was a sketch of a fixed wing aircraft. On the back of the disk was a diagram of the
forces of lift, drag and thrust acting on a flying body. It was the Wright brothers
who made the dream of powered flight a reality. On December 17, 1903, in Kitty Hawk, North
Carolina. Orville climbed aboard the Flyer I andthrottled up the engine. The machine
accelerated along the rail on which it taxied for launch, lifted from the trolley and flew
for approximately twelve seconds, covering 120 feet before touching down. Since the first powered
flight in 1903 to the present there has been one mind boggling advancement after another
in the field of aviation. The structures have become more durable and the engines have
become more powerful. As engineers came to better understand the principals of flight and
materials have become more sophisticated, aircraft became faster, more maneuverable and
able to carry larger loads. Whether one studies the
Wright Flyer I or a modern jet such as an F-18, if an aircraft is to prove airworthy it
must be designed and built within the restrictions of certain physical properties. To
design an aircraft which will fly, the designer must have a full understanding of the
pricipals of lift, drag, stall, dihedral, weight and center of gravity. How can an aircraft sit on
a runway, held fast by the powerful force of gravity and yet still be able to lift off the
runway and defy this force? To understand this a good place to start is with and
understanding of Bernoulli's Principal. The definition of Bernoulli's Principal is as
follows: When the speed of a fluid
increases, the pressure in the fluid decreases, and when the speed of a fluid decreases
the pressure in the fluid increases. Air, in the study of aeronautics, is considered a
fluid since it contains molecules which can flow over a surface. An airfoil is designed so
oncoming air is forced to travel a longer distance over the airfoil than below it. If the
air travels farther then it will be forced to travel faster over the airfoil. The air
travelling faster over the airfoil will cause a low pressure area in the air over the
airfoil. The air travelling under the airfoil travels comparably slower which will result
in a high pressure area under the airfoil. The low pressure area over the wing pulls the
wing up toward it while the high pressure area under the wing pushes the wing up.
There is another method
designers use to gain lift in their designs. This method is by increasing the angle of
attic of the wing. The angle of attack is the angle between the oncoming airflow and the
airfoil. At airspeed an increased angle of attack causes the air to flow faster over the
top of the wing than below, thus the amount of lift is increased.
However if the angle of
attack is increased too much, the streamlined flow of air is broken up and the air begins
to whirl in pockets over the airfoil. These pockets of air are called eddies. Once eddies
form over a wing the amount of lift suddenly decreases and the wing is said to stall. It
in effect stops flying. This is somewhat usefull in aerobatics.
Thrust is the energy
expended to move an aircraft forward. There are basically two methods used to provide
thrust in powered aircraft, the internal combustion engine and the jet engine. An internal
combustion engine is similar to a car engine. An internal combustion engine uses a
propeller to push or pull the aircraft forward. The jet engine works on the principal of
pressurized gasses being forced through ducts or vents at the rear of the aircraft
resulting in the aircraft being propelled forward. Stall occurs when the lift
surfaces of a wing can no longer provide enough lift to overcome the weight of the
aircraft and keep it airborne. In a stall and aircraft will lose altitude rapidly. Stall
is one of the major causes of small aircraft crashes. A stall may occur if the angle of
attack of the wing is too high, as mentioned earlier or is the airspeed of the aircraft is
reduced. If a plane slows to a point at which the air flowing over the airfoil no longer
provides enough lift, the plane will stall. Dihedral is the angle of
the wing in relation to the fuselage of the aircraft. Dihedral improves the stability of
the aircraft. The dihedral of a wing provides stability of the aircraft along the
longitudinal axis.
The weight of an aircraft
provides the downward force placed on the craft. Gravity is the force responsible for
this. As a result of this force the distribution of weight is an improtant factor. If the
center of gravity placed so the weight of the plane will be balanced, the most efficient
design can be acheived. If the weight is too far forward the plane will have a tendency to
dive. If the weight is placed too far to the rear the plane will have a tendency to hold
it's nose up and possibly stall. The aeronautical engineer
uses many vocabulary terms which must be understood to successfully design an aircraft.
These terms fall under the following headings: Parts of an aircraft Control surfaces of an
aircraft Dimensions of an aircraft Airplane axes Parts of an aircraft
There are specific terms
used when describing the parts of an aircraft. The fuselage is the main
body of the aircraft. The wing is that portion of the craft that contains
the airfoil and provides the lift that allows the aircraft to fly. The horizontal
stabilizer provides lift for the rear of the plane to assist in maintaining level
flight. The vertical stabilizer or fin assists the plane in maintaining a
straight flight.
Control Surfaces of an aircraft
The control surfaces of an
aircraft include the rudder, the elevator and the ailerons. The rudder is
located at the rear of the vertical stabilizer. The rudder allows the plane to rotate on
its vertical axis. The elevator is located at the rear of the horizontal
stabilizer. The elevator allows the aircraft to rotate on its lateral axis. The ailerons
are located at the rear of the main wing. The ailerons allow the plane to rotate on its
longitudinal axis.
When a plane is in flight
we think of it being controlled on the three axes mentioned above. The longitudinal axis
is the imaginary line running from the extreme nose to the extreme tail of the plane. The
ailerons control the movement of the plane about this axis. Movement about this axis is
called roll. The lateral axis runs from
wingtip to wingtip at the center of gravity point. Movement on this axis is controlled by
the elevator which causes the nose to move up or down. This movement is called pitch. The vertical axis runs
through the top of the plane and out the bottom, intersecting the two axes. Rotation about
this axis is controlled by the rudder which causes the nose to move left and right. This
movement is called yaw. Dimensions of an aircraft
The dimensions of an
aircraft are referred to by the following terms: Length:
The distance from the nose to the tail Wingspan: The distance from one
wingtip to the other. Wing chord: The distance from the
leading edge of the wing to the trailing edge of the wing. Angle of incidence: The angle of the wing in
relation to the horizontal plane of the aircraft provides the angle of attack. Dihedral Angle: The angle of the wing from
the wingtip to the center of the wing. |
