|By Allen Martis, USA [ Published Date: May 17, 2005 ]|
The dream of flying is as old as mankind itself. However, the concept of the airplane has only been around for two centuries. Before that time, men and women tried to navigate the air by imitating the birds. They built machines with flapping wings called ornithopters. On the surface, it seemed like a good plan. After all, there are plenty of birds in the air to show that the concept does work.
The trouble is, it works better at bird-scale than it does at the much larger scale needed to lift both a man and a machine off the ground. So folks began to look for other ways to fly. Beginning in 1783, a few aeronauts made daring, uncontrolled flights in lighter-than-air balloons, but this was hardly a practical way to fly. There was no way to get from here to there unless the wind was blowing in the desired direction.
It wasnít until the turn of the nineteenth century that an English baronet from the gloomy moors of Yorkshire conceived a flying machine with fixed wings, a propulsion system, and movable control surfaces. This was the fundamental concept of the airplane. In 1804, Sir George Cayley built the first true airplane - a kite mounted on a stick with a movable tail but it was an unmanned airplane. Between 1899 and 1905, the Wright brothers conducted a program of aeronautical research and experimentation that led to the first successful powered airplane in 1903 and a refined, practical flying machine two years later. All successful airplanes since then have incorporated the basic design elements of the 1903 Wright Flyer.
Iíve always been fascinated by how an airplane flies in the air defying gravity. It is interesting to learn how an airplane is designed to speed off into the sky carrying with it passengers, loads of cargo and tons of steel used in the construction of an airplane.
The four aerodynamic forces that act upon an airplane in flight are lift (the upward acting force), weight (or gravity, the downward acting force), thrust (the forward acting force), and drag (the air resistance or backward acting force). These four forces are continuously battling each other while an airplane is in flight.
Gravity opposes lift, thrust opposes drag. In order to take off, the aircraft's thrust and lift must be sufficient to overcome its weight and drag. In level flight at constant speed, thrust exactly equals drag and lift exactly equals the pull of gravity. To land, an aircraft's thrust must be reduced safely below its drag, as its lift is reduced to levels less than its weight.
How an Airplane Generates Lift
Lift is the aerodynamic force that counteracts gravity and holds an airplane in the air. Most of the lift required by an airplane is created by its wings, but a certain portion is also generated by other parts of the aircraft, such as the fuselage. But what actually causes the lift to be created?
First, understand that air is a fluid, just like water, and that all fluids adhere to the same physical and mathematical principles. Next, realize that lift can only be generated when a fluid is in motion. For example, a wing must be passing through the air or the air must be moving around a stationary wing, one or the other. (The way it usually happens is that the wing is doing most of the moving, although the air may be moving too, at the same time.)
Most airplane wings have a special, basic shape: their upper surfaces are curved and their lower surfaces are flatter. This shape is what works with the fluid motion of the air to create lift. As air moves around a wing, some goes over the top and some goes underneath. The air that goes over the curved upper surface undergoes two important changes: it is reduced in pressure (by the centrifugal force of flowing across the curved surface) and it is accelerated downward (as it leaves the trailing edge of the wing). The wing is forced into the region of reduced air pressure above the upper surface of the wing by the higher air pressure beneath the wing. Also, the downward acceleration of the air (downwash) at the trailing edge forces the wing upward.
Since lift is dependant on the motion of the air, it increases as the speed of the air increases. Lift also increases (to a point) as the angle that the wing makes with the airflow (known as the angle of attack) increases. Past a certain point, however, increased angle of attack will cause the wing to suddenly lose its lifting ability, or stall.
Control Surfaces and Maneuvering
An airplane in flight moves around three axes of rotation: longitudinal axis, lateral axis, and vertical axis. These axes are imaginary lines that run perpendicularly to each other through the center of gravity of the airplane. Rotation around the longitudinal axis (the line from the nose of the plane to the tail) is called roll. Rotation around the lateral axis (the line from wingtip to wingtip) is called pitch. Rotation around the vertical axis (the line from beneath to above the plane) is called yaw. The pilot guides and controls the aircraft by controlling its pitch, roll, and yaw via the control surfaces. These include the ailerons, elevators, and rudder.
The ailerons on an airplane's wings control roll around the longitudinal axis. They work together, simultaneously, tied to the control wheel, or stick, in the cockpit. When the control wheel is turned left, the aileron on the left wing goes up and the one on the right wing goes down. The opposite occurs when the wheel is turned right. But how does this make the airplane roll? The ailerons alter the lifting ability of the wings slightly. When an aileron is lowered, the lift on the outer portion of that wing increases, causing that wing to rise a little. When an aileron is raised, the lift on the outer portion of that wing is decreased slightly, causing that wing to drop a little. Since the ailerons on an airplane work together, their action causes the airplane to roll.
The elevators on the horizontal portion of the tail of an airplane control the pitch of the plane, or its motion around the lateral axis. They are also tied to the control wheel in the cockpit. When the wheel is pulled back, the elevators move upward, causing the tail of the plane to move downward and the nose to pitch upward. When the wheel is pushed forward, the elevators move downward, causing the tail of the plane to rise and the nose to pitch downward. The elevators work like the ailerons on the wings, in that they cause changes in the lift generated by the tail of the plane. Also, the elevators work together, simultaneously, like the ailerons, but they do not work in opposition to one another. Both go up when the control wheel is pulled back and both go down when the control wheel is pushed forward.
The rudder on the rear edge of the vertical fin on the airplane's tail controls yaw around the vertical axis. It is connected to the pedals at the pilot's feet. Pushing the right pedal causes the rudder to deflect to the right. This makes the tail of the airplane move toward the left, causing the nose to move to the right. Pushing the left pedal makes the rudder deflect to the left, the tail moves to the right, and the nose points to the left. Although the rudder pedals and control wheel in the cockpit are not linked together, they must be used simultaneously to control the plane. The pilot guides the airplane by careful and precise movements of the control wheel and rudder pedals, as well as adjusting the thrust of the aircraft.
How Does an Airplane Produce Thrust?
Thrust is the force created by propellers or jet engines that overcomes the airplane's aerodynamic drag (its resistance to passing through the air) and gives it forward motion. This force can either "pull" or "push" the aircraft forward, depending on the type of power source used.
What would the world be like if there were no airplanes? In the 100 years since airplanes were invented, they have changed the world so much it would be hard to imagine what life would be like without them. Without airplanes, the world would be a bigger, slower place. Travel that takes place in an afternoon on an airplane would take days or weeks without them. If all the people flying for business or pleasure were driving, there would be more cars on the road. Moving the cargo would also put more trucks and trains on the roads/rails, and result in more accidents. Therefore the increased land-based traffic would mean more people would be hurt in traffic accidents.
Airplanes have made commerce around the world very practical and convenient, and have been a major influence in integrating the world's populations. People are able to visit and live in places they otherwise could not. Thus, in general, people have become more knowledgeable, aware, and accepting of others. Without airplane, the world would seem much bigger because it would take much longer to travel great distances.