Ever since I was little I was amazed at the ability for a machine to fly. I have always wanted to explore ideas of flight and be able to actually fly. I think I may have found my childhood fantasy in the world of aeronautical engineering. The object of my paper is to give me more insight on my future career as an aeronautical engineer. This paper was also to give me ideas of the physics of flight and be to apply those physics of flight to compete in a high school competition.
History of Flight
The history of flying dates back as early as the fifteenth century. A Renaissance man named Leonardo da Vinci introduced a flying machine known as the ornithopter. Da Vinci proposed the idea of a machine that had bird like flying capabilities. Today no ornithopters exist due to the restrictions of humans, and that the ornithopters just aren’t practical. During the eighteenth century a philosopher named Sir George Cayley had practical ideas of modern aircraft. Cayley never really designed any workable aircraft, but had many incredible ideas such as lift, thrust, and rigid wings to provide for lift. In the late nineteenth century the progress of aircraft picks up. Several designers such as Henson and Langley, both paved the way for the early 1900’s aircraft design. Two of the most important people in history of flight were the Wright Brothers. The Wright Brothers were given the nickname the “fathers of the heavier than air flying machine” for their numerous flights at their estate in Kitty Hawk, North Carolina. Orville and Wilbur Wright created a motor-powered biplane in which they established incredible feats of the time. The Wright Brothers perfected their design of the heavier than air flying machine, and eventually sold their idea to the U.S. military. The airplane does not become important until the end of World War I. Towards the end of the War the airplane becomes a practical device of war being able to carry weapons. Anthony Fokker and Louis Bleriot create the most successful of early modern biplanes known as the D-VII and D-VIII. Biplanes are eventually taken over by the monoplane, or one wing. This new design allowed for faster flight and better visibility for the pilot. Air-cooled engines lead the way for commercial aircraft, and Boeing introduces the first modern airliner the 247. Airplanes are effected the greatest by supply and demand of war. New styles of war begun to emerge so did new and improved types of aircraft. The population of the U.S. also begun to grow which leads to the modern most sophisticated commercial airliner the 777. Most aircraft improvements are found in the military and intelligence field. The most high tech aircraft known today for such things as spying are the SR-71 Blackbird, and the U-2 Spy plane. The most complicated and best aircraft performance is still held by the space shuttle and probably always will be. The last 200 years have seen incredible changes in aircraft from the man with wings to heavier than air flying machines that can travel at supersonic speeds.
Every single part of an aircraft is incredibly important, without a piece of the airplane it just wouldn’t fly. If there had to be a most important part of the aircraft, it would mostly likely have to be the wing. The wing allows a heavier than air (unlike hot air balloons) machine to fly. The principle that allows a heavier than air machine to fly is the principle of Bernoulli. Daniel Bernoulli came up with idea using water tests that low pressure over high pressure would cause something to rise, or lift. Bernoulli had no idea of the effect it would have on a flying machine. Bernoulli died in 1782 and the first airplane wasn’t even designed until the late 1800’s. Bernoulli had never seen his application of water pressure, but his principle became the basic principle behind all heavier than air machines. Several aspects of a wing are necessary for flight. The wing must have a long enough span that the lift will counter act the force of gravity. The wing must be shaped in a foil design so that it produces lots of lift and less drag. There are many different shapes of wings, and foil designs all serving different purposes. The most commonly used foil design is a wing with a flat bottom and the top must be curved upward more drastically towards the front and sloping down to a point towards the end (a diagram of a foil design is shown in page 10).
Another important aspect of flight is the opposite of forward motion called drag. Drag can be seen in almost everyday life. An example of drag would be swimming in a pool. As you dive in the water the water must displace around you therefore causing two kinds of friction and slowing you down. The two types of drag friction that aircraft deal with are pressure drag and skin friction drag. An example of pressure drag is the air that hits the frontal part of the wing, or the most forward flat part of the wing and causes the plane to slow down. An example of skin friction is the actual air moving over the wing and being slowed down by the skin of the wing. There are a few other types of drag called induced drag. Induced drag basically means that drag caused by lift. Since the plane moves upward during lift the plane also has to displace air above the wing. Another type of induced drag is the drag caused by the wing tips. As the aircraft lifts off the ground air wants to move onto the top of the wing rather than stay on the bottom (equalize pressure). The wing tips actually allow the air on the bottom of the wing to travel to the top in a sideward motion or around the wing tip. When this happens the air from the bottom of the wing pushes down on the wing forcing the airplane to want to go down. “The only way to eliminate wing tip drag is to have a wing of infinite size, which is impossible because lift would not be effective (Smith 77).” All of the different kinds of drag play a great role in the designing of the aircraft, and its efficiency. Drag has its biggest effect on the fuselage, or the body of the aircraft because of its large size. Since all types of aircraft have mass it is impossible to eliminate all drag; therefore aircraft must be designed to use drag to their advantage, or be efficient enough that lift over powers drag.
Another extremely important element in flight is thrust. For flight to ever occur there must be some kind of initial force to force air over the wings creating lift. This initial force is usually found in the form of a propeller or a jet engine. An exception to those forms of thrust is a glider. A glider still needs an initial force to begin flight, which is usually found in a tow plane. The most commonly used thrust mechanism is a propeller. The propeller will continue to be the most commonly used because of its effectiveness and cheapness. Due to the jet engines high cost and high speeds it will remain primarily a military aircraft power plant. The physics of thrust used in aircraft is semi-complicated. Firstly, in the case of the propeller the propeller must be large enough to displace or pull enough air to keep the aircraft in flight. On the other hand jet engines must be able to displace a small amount of air at much higher speeds than the propeller. As an aircraft speeds up in must displace air at faster amounts causing more drag. This factor creates a barrier of speed within the Earth’s atmosphere. Although some aircraft do come extremely close to this barrier of speed such as the SR-71 and the space shuttle. The SR-71 or surveillance aircraft can reach speeds of over mach two, or two times the speed of sound approximately 14,000mph. The space shuttle on the other hand can reach speeds of over mach five, or 36,000mph while orbiting the Earth. Both are extremely fast and made of strong, lightweight, and fire retardant materials. Today new designs for propulsion is being created such as thrust vectoring. Thrust vectoring is the ability for a jet engine to change the direction of air changing the direction of flight without using the rudder. In conclusion, without thrust or an initial power source flight is not possible.
Stability and Control
Stability of an aircraft during flight is crucial. To understand stability one must imagine a three-space Cartesian coordinate system, or 3-D space. The aircraft must be controlled on its entire axis, x, y, and z. In order to keep a straight flight a rudder or vertical stabilizer must be added to the rear of the aircraft. For unhampered flight on the horizontal plane horizontal stabilizers must be added to the rear of the aircraft. Nothing needs to be added to nose of the aircraft due to the thrust of the engine. All stabilizers are important on an aircraft without one the aircraft would just spin out of control. This is seen often when a helicopter spins out of control when the tail fan loses power. In all cases the torque of the propeller would cause an induced spin and the outcome would be disaster. New designs in stabilizer technology have allowed for lightweight aircraft to be produced. Instead of having a horizontal stabilizer and a vertical stabilizer both is put together to give just two small stabilizers emanating from the fuselage at forty-five degree angles eliminating the need for three stabilizers. The pilot has the ability to control the aircraft’s entire axis by two control devices called a pedal and a stick, or a specialized steering wheel. Making the stick one of the most important devices inside a cockpit.
High Speed Flight
Minimal speed flight and high-speed flight vary in several degrees. An important aspect of this variation is related to the speed of sound. The speed of sound or sound barrier is the speed of sound moving through a given space. The actual speed of sound is varied at different altitudes due to the density of air, and how much air sound has to displace. At sea level the speed of sound is approximately 761 mph. In the early 1940’s the sound barrier seemed almost impossible until the X wing class experimental aircraft had been developed. The speed of sound was unattainable by a conventional propeller; therefore new kinds of thrust had to be developed known as the jet engine. The jet engine carried aircraft into a new age of flight. The first aircraft to reach the speed of sound was the X-1 flown by the famous Chuck Yeager on October 14, 1947. The X-1 was shaped like a bullet because at the time it was believed to be the most aerodynamic design. The X-1 found out several important changes in flight during, before, and after an aircraft reaches the speed of sound. The X-1 found out that when an aircraft reaches the speed of sound it is at a very unstable point of flight, but before or after the speed of sound the flight was more stable. They also found out about shock waves and how they affect flight. “In order to understand how high speed affects the compressibility of the air, let us consider an example of wave motion. Suppose we drop pebbles into a pool of water and observe the waves resulting from these disturbances. If we drop all pebbles at the same spot, but placed at equal time intervals, the waves would all spread out from a single point. The outermost wave would be from the first pebble, the next wave from the second, and so on. Now suppose that we drop the pebbles at the same time interval but slowly move to the right as we drop them. Notice that the waves are moving faster than our forward speed. Finally, we proceed at a rate faster than the waves are able to move. Each pebble hits outside of the wave made by the previous pebble. Just as we drop the fourth pebble, the waves pile up at the forefront of our motion and tend to reinforce each other (Smith 191-192).” These shock waves build up on the nose of the aircraft creating a disturbance over the wings. The Concord has a bendable nose so at supersonic flight it can reduce the disturbance over the wing to allow a more steady and smooth flight. Another way to decrease the disturbance over the wings are to move the wings lower than the horizontal stabilizer or visa versa to allow the shock waves moving over each wing to miss each other. Most aircraft today do not have enough fuel to maintain the speed of sound for great distances. Engineers have designed a brand new aircraft known as the F-22, which has the ability to fly an entire mission at supersonic speeds. The speed of light is unattainable by aircraft due to drag. We have no materials that could with stand the heat caused by the friction of the air moving over its body, nor materials strong enough to be able to take the enormous drag. Today there is no thrust capability that would allow for the speed of light. Although aircraft has proved such things as time dilation it is still impossible for an aircraft to travel at 900,000 miles per second.