Man has been fascinated with flight from the beginning of recorded history. Orville and Wilbur Wright are credited with the first powered, controlled flight. There were many who preceded the Wright Brothers who dreamed of flying.
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 useful 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
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.
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.
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.