Here Is The Famous Aviation Alphabet
Human Flight has become a tired fact of modern life. At any given moment, roughly 5,000 airplanes crisscross the skies above the United States alone, amounting to an estimated 64 million commercial and private takeoffs every year [source:NATCA]. Consider the rest of the world's flight activity, and the grand total is incalculable.
It is easy to take the physics of flight for granted, as well as the ways in which we exploit them to achieve flight. We often glimpse a plane in the sky with no greater understanding of the principles involved than a caveman.
How do these heavy machines take to the air? To answer that question, we have to enter the world of fluid mechanics.
Physicists classify both liquids and gases as fluids, based on how they flow. Even though air, water and pancake syrup may seem like very different substances, they all conform to the same set of mathematical relationships. In fact, basic aerodynamic tests are sometimes performed underwater. To put it simply, a salmon essentially flies through the sea, and a pelican swims through the air.
The core of the matter is this: Even a clear sky isn't empty. Our atmosphere is a massive fluid layer, and the right application of physics makes it possible for humans to traverse it.
In this article, we'll walk through the basic principles of aviation and the various forces at work in any given flight.
It is easy to take the physics of flight for granted, as well as the ways in which we exploit them to achieve flight. We often glimpse a plane in the sky with no greater understanding of the principles involved than a caveman.
How do these heavy machines take to the air? To answer that question, we have to enter the world of fluid mechanics.
Physicists classify both liquids and gases as fluids, based on how they flow. Even though air, water and pancake syrup may seem like very different substances, they all conform to the same set of mathematical relationships. In fact, basic aerodynamic tests are sometimes performed underwater. To put it simply, a salmon essentially flies through the sea, and a pelican swims through the air.
The core of the matter is this: Even a clear sky isn't empty. Our atmosphere is a massive fluid layer, and the right application of physics makes it possible for humans to traverse it.
In this article, we'll walk through the basic principles of aviation and the various forces at work in any given flight.
1: Fueling Flight: Means of Propulsion
![Picture](/uploads/2/5/5/5/25558210/4047554.jpg?293)
When it comes to propelling an airplane through the sky, different designs depend on different means of propulsion to provide thrust. Most methods, however, work along the same basic principle: An engine accelerates a gas.
Let's peek inside a few different engines.
Propeller engine: In a typical propulsion system, an engine mixes fuel with air and burns the fuel to release the energy. The resulting heated gas moves a piston, which is attached to a crankshaft. This spins a propeller, or prop, which is essentially an array of spinning wings. Each blade is an airfoil with an angle of attack. The angle is greater toward the center because the speed of the propeller through the air is slower close to the hub. Many larger prop-driven aircraft boast propellers with adjustable pitch mechanisms. These mechanisms let the pilot adjust the propeller's angle of attack depending on air speed and altitude. There are, of course, variations. For example, in turbo prop planes, a gas turbine spins the propeller, and electric aircraft designs don't employ combustion.
Rocket engine: While a propeller engine uses the surrounding air as the working fluid of its propulsion, all a rocket needs is the thrust of its own combustion exhaust gas. This is why a rocket can provide thrust in space, but a propeller cannot. A rocket engine combines fuel and an internal source of oxygen called anoxidizer. The oxygen and fuel ignite in a combustion chamber, exploding in a hot exhaust. These gases pass through a nozzle to produce thrust.
Gas turbine engine: Also known as a jet engine, this means of propulsion works a lot like a rocket engine, only it obtains the necessary air from the surrounding atmosphere rather than a tank. As such, jet engines don't work in space either. Many variants of gas turbine engines, such as those seen on most airliners, collect the necessary air through fanlike rotary compressors. A ramjet, however, doesn't use a compressor. Instead, the airplane builds up speed, which forces air through forward-facing vents in the engine. In this model, the aircraft's speed naturally compresses the air necessary for combustion.
Now that we've covered engines, let's get some serious speed.
Let's peek inside a few different engines.
Propeller engine: In a typical propulsion system, an engine mixes fuel with air and burns the fuel to release the energy. The resulting heated gas moves a piston, which is attached to a crankshaft. This spins a propeller, or prop, which is essentially an array of spinning wings. Each blade is an airfoil with an angle of attack. The angle is greater toward the center because the speed of the propeller through the air is slower close to the hub. Many larger prop-driven aircraft boast propellers with adjustable pitch mechanisms. These mechanisms let the pilot adjust the propeller's angle of attack depending on air speed and altitude. There are, of course, variations. For example, in turbo prop planes, a gas turbine spins the propeller, and electric aircraft designs don't employ combustion.
Rocket engine: While a propeller engine uses the surrounding air as the working fluid of its propulsion, all a rocket needs is the thrust of its own combustion exhaust gas. This is why a rocket can provide thrust in space, but a propeller cannot. A rocket engine combines fuel and an internal source of oxygen called anoxidizer. The oxygen and fuel ignite in a combustion chamber, exploding in a hot exhaust. These gases pass through a nozzle to produce thrust.
Gas turbine engine: Also known as a jet engine, this means of propulsion works a lot like a rocket engine, only it obtains the necessary air from the surrounding atmosphere rather than a tank. As such, jet engines don't work in space either. Many variants of gas turbine engines, such as those seen on most airliners, collect the necessary air through fanlike rotary compressors. A ramjet, however, doesn't use a compressor. Instead, the airplane builds up speed, which forces air through forward-facing vents in the engine. In this model, the aircraft's speed naturally compresses the air necessary for combustion.
Now that we've covered engines, let's get some serious speed.
2: High Aircraft Speed
![Picture](/uploads/2/5/5/5/25558210/1341583.jpg?425)
Once fueled, an airplane's minimum flight speed depends on the movement of the air around it. Maximum airspeed, on the other hand, is limited largely by technology. We use the speed of soundas the ultimate measuring stick for airplane velocity, and this is quite simply the rate at which a sound wave moves through a gas.
The exact speed of sound depends on the elasticity and density of the gas medium it's traveling through -- which means varying air pressure and air temperature prevent the existence of a global speed of sound. At 32 degrees Fahrenheit (0 degrees Celsius), the speed of sound in air is 1,087 feet per second (331 meters per second). Raise the temperature to 68 degrees Fahrenheit (20 degrees Celsius), and the speed climbs to 1,127 feet per second (343 meters per second).
Whatever the details of the medium, we refer to the speed of sound as Mach 1, named after physicist Ernst Mach. If an airplane reaches the speed of sound, its speed is Mach 1. If the airplane reaches double the speed of sound, its speed is Mach 2.
(An F/A-18 Hornet from a cloud created when it broke the sound barrier)
Airplanes speeds that are less than Mach 1 are considered subsonic speeds, while those very close to Mach 1 are said to be transonic. Velocities surpassing the speed of sound are divided into high supersonic (Mach 3 through Mach 5) and hypersonic (Mach 5 through Mach 10). Speeds swifter than Mach 10 are considered high hypersonic.
If you've ever heard a supersonic aircraft fly overhead, then you've probably heard a sonic boom. Once an airplane attains Mach 1, the sound waves emitted by the plane can't speed ahead of it. Instead, these waves accumulate in a cone of sound behind the plane. When this cone passes overhead, you hear all that accumulated sound at once.
We'll head inside the airplane next to investigate which cabin systems work to keep us healthy at high altitudes.
The exact speed of sound depends on the elasticity and density of the gas medium it's traveling through -- which means varying air pressure and air temperature prevent the existence of a global speed of sound. At 32 degrees Fahrenheit (0 degrees Celsius), the speed of sound in air is 1,087 feet per second (331 meters per second). Raise the temperature to 68 degrees Fahrenheit (20 degrees Celsius), and the speed climbs to 1,127 feet per second (343 meters per second).
Whatever the details of the medium, we refer to the speed of sound as Mach 1, named after physicist Ernst Mach. If an airplane reaches the speed of sound, its speed is Mach 1. If the airplane reaches double the speed of sound, its speed is Mach 2.
(An F/A-18 Hornet from a cloud created when it broke the sound barrier)
Airplanes speeds that are less than Mach 1 are considered subsonic speeds, while those very close to Mach 1 are said to be transonic. Velocities surpassing the speed of sound are divided into high supersonic (Mach 3 through Mach 5) and hypersonic (Mach 5 through Mach 10). Speeds swifter than Mach 10 are considered high hypersonic.
If you've ever heard a supersonic aircraft fly overhead, then you've probably heard a sonic boom. Once an airplane attains Mach 1, the sound waves emitted by the plane can't speed ahead of it. Instead, these waves accumulate in a cone of sound behind the plane. When this cone passes overhead, you hear all that accumulated sound at once.
We'll head inside the airplane next to investigate which cabin systems work to keep us healthy at high altitudes.
3: Under (Cabin) Pressure
Sure, humans evolved to thrive in Earth's atmosphere, but it's important to realize that we only evolved to thrive in a thin layer of the planet's gaseous outer layer. Air pressure changes depending on altitude. In the same way that the water pressure in the ocean is greater on the seafloor than it is just below the surface, air pressure decreases the higher you ascend through the atmosphere.
When humans breathe thinner, high-altitude air, they have a harder time taking in enough oxygen. And when we hang out at heights higher than 9,800 feet (3,000 meters), our bodies become susceptible to a host of unpleasant or even deadly illnesses, like these:
Altitude sickness: Also the bane of high-altitude mountain climbers, reduced air pressure and lower oxygen concentration levels can cause extreme shortness of breath due to fluid buildup in the lungs. In extreme cases, this can lead to brain swelling, resulting in confusion, coma or death.
Ear barotrauma: The Eustachian tube connects your middle ear to the outside world. If this tube becomes blocked, changes in atmospheric pressure can cause a pressure differential that can result in dizziness, discomfort, hearing loss, ear pain and nose bleeds.
Decompression sickness: Divers know this condition as the bends, and it can occur in the air, as well as in the water. Exposure to low barometric pressures can cause dissolved nitrogen in the blood stream to form harmful bubbles that can cause everything from drowsiness to stroke.
Hypoxia: As low pressure means less oxygen in every breath you breathe, the brain receives less oxygen at high altitudes. The physiological results often include cognitive impairment or light-headedness, which can seriously impair a pilot's ability to fly the plane.
Pressurized cabins enable pilots, crew and passengers to avoid these pitfalls of flying at high altitude. While the air outside the cabin thins out the higher a plane climbs, compressed air inside the cabin maintains more surface-level air pressure and oxygen-rich air. In the event of accidental loss of cabin pressure, emergency oxygen masks provide the necessary air quality.
Pressurized flight suits achieve the same effect as pressurized cabins, only on an individual basis. Characterized by enclosed helmets, these suits typically see use in military and high-performance aircraft.
When humans breathe thinner, high-altitude air, they have a harder time taking in enough oxygen. And when we hang out at heights higher than 9,800 feet (3,000 meters), our bodies become susceptible to a host of unpleasant or even deadly illnesses, like these:
Altitude sickness: Also the bane of high-altitude mountain climbers, reduced air pressure and lower oxygen concentration levels can cause extreme shortness of breath due to fluid buildup in the lungs. In extreme cases, this can lead to brain swelling, resulting in confusion, coma or death.
Ear barotrauma: The Eustachian tube connects your middle ear to the outside world. If this tube becomes blocked, changes in atmospheric pressure can cause a pressure differential that can result in dizziness, discomfort, hearing loss, ear pain and nose bleeds.
Decompression sickness: Divers know this condition as the bends, and it can occur in the air, as well as in the water. Exposure to low barometric pressures can cause dissolved nitrogen in the blood stream to form harmful bubbles that can cause everything from drowsiness to stroke.
Hypoxia: As low pressure means less oxygen in every breath you breathe, the brain receives less oxygen at high altitudes. The physiological results often include cognitive impairment or light-headedness, which can seriously impair a pilot's ability to fly the plane.
Pressurized cabins enable pilots, crew and passengers to avoid these pitfalls of flying at high altitude. While the air outside the cabin thins out the higher a plane climbs, compressed air inside the cabin maintains more surface-level air pressure and oxygen-rich air. In the event of accidental loss of cabin pressure, emergency oxygen masks provide the necessary air quality.
Pressurized flight suits achieve the same effect as pressurized cabins, only on an individual basis. Characterized by enclosed helmets, these suits typically see use in military and high-performance aircraft.
4: Landing Gear
![Picture](/uploads/2/5/5/5/25558210/8574440.jpg?505)
We've discussed the parts of an airplane necessary for flight, but just as a bird eventually needs to stretch its legs, so too does an airplane require some form of landing gear. The gear in turn requires anundercarriage, or a structure that supports the plane's weight on the ground.
The Wright brothers' 1903 flyer depended on simple wooden skids for landing in the sand. Other more modern craft to possess landing skids include the German Messerschmitt ME 163 Komet, aWorld War II rocket-propelled interceptor, and the U.S. Air Force's X-15, an experimental, high-speed 1960s jet. Along similar lines, some aircraft boast floats or skis for landing on water, snow or ice.
When you think of landing gear, however, you probably think of the wheeled variety. The actual wheels involved have ranged over the vast spectrum of aviation designs. Some early landing gear resembled bicycle wheels while larger aircraft often feature bogie landing gear that employ sets of four or more wheels on each brace. During the 1950s, the U.S. Air Force even experimented with tank-style tracked landing gear for the enormous six-engine Convair B-36 Peacemaker.
Regardless of the type of wheel employed, such landing gear are typically arranged in one of two arrangements. First there's the conventional undercarriage with two front wheels and one smaller tail wheel or skid. You can spot this arrangement, also known as a taildragger undercarriage, on older prop-driven aircraft. Most modern planes use a tricycle undercarriage, in which the smaller wheel is positioned at the front of an aircraft.
Variations on these two basic themes are numerous, with additional wheels added depending on the particular demands of a given aircraft. The Lockheed U-2, for instance, features a tandem design with two fuselage wheels running down the middle and supporting wheels on each wing for balance. Many modern aircraft feature retractable landing gear, which pull up into fuselage during flight, but others still featurefixed landing gear that remain extended all the time.
The Wright brothers' 1903 flyer depended on simple wooden skids for landing in the sand. Other more modern craft to possess landing skids include the German Messerschmitt ME 163 Komet, aWorld War II rocket-propelled interceptor, and the U.S. Air Force's X-15, an experimental, high-speed 1960s jet. Along similar lines, some aircraft boast floats or skis for landing on water, snow or ice.
When you think of landing gear, however, you probably think of the wheeled variety. The actual wheels involved have ranged over the vast spectrum of aviation designs. Some early landing gear resembled bicycle wheels while larger aircraft often feature bogie landing gear that employ sets of four or more wheels on each brace. During the 1950s, the U.S. Air Force even experimented with tank-style tracked landing gear for the enormous six-engine Convair B-36 Peacemaker.
Regardless of the type of wheel employed, such landing gear are typically arranged in one of two arrangements. First there's the conventional undercarriage with two front wheels and one smaller tail wheel or skid. You can spot this arrangement, also known as a taildragger undercarriage, on older prop-driven aircraft. Most modern planes use a tricycle undercarriage, in which the smaller wheel is positioned at the front of an aircraft.
Variations on these two basic themes are numerous, with additional wheels added depending on the particular demands of a given aircraft. The Lockheed U-2, for instance, features a tandem design with two fuselage wheels running down the middle and supporting wheels on each wing for balance. Many modern aircraft feature retractable landing gear, which pull up into fuselage during flight, but others still featurefixed landing gear that remain extended all the time.