The concept of jet propulsion has been understood for thousands of years across many cultures. Ancient Greece understood how ejected steam could make an object spin, and the Chinese invented rocketry in the form of fireworks and projectile weapons. It wasn't until the twentieth century, however, that jet engines became useful for flight. The first jet-powered airplane was successfully tested in Germany in 1939, the dawn of World War II, and the first jet-to-jet dogfight was fought between Korea and the United States in 1950. In the 1950s and 1960s, jets became more common in commercial flights, and by the 1970s the jet was improved to such a degree that it all but replaced the piston engine. Today, the jet is taken for granted as the most efficient way to travel long distances at high altitudes, at velocities approaching and even far exceeding the speed of sound.
Jets are the most economical way of traveling long distances, first because they are fast. Commercial airlines tend to be about 10 times faster than cars for intracontinental travel, and they are almost the only mode of intercontinental travel in wide use. Jets are also cheap from a consumer standpoint. Some airlines offer flights of hundreds or even thousands of miles for less than a hundred dollars. Compare that to the money a person spends on car gasoline and maintenance--not to mention the greater amount of time taken off from work to travel--and the economic superiority of flying versus driving becomes indisputable.
Jets operate on Newton's third law, which states that every action results in an equal and opposite reaction. First, a fan at the front of the engine spins, sucking in atmospheric air, which immediately separates into two columns: an outer column and an inner column. The outer column goes directly toward the back of the engine, where it is expelled to help produce thrust. The inner column of air goes into a compression chamber of powerful fans that squash the air. This hot, dense air moves into the combustion chamber, where the stream is continually ignited along with jet-grade gasoline. The ignited air and gasoline enter the turbines, causing them to spin, which in turn spins the compressor and fan up front. The cold and hot air then combine in the mixer near the back (to quiet the engine; burning hot air is louder than cold). Finally, all this processed air moves past a cone-shaped nozzle and blasts out the back of the engine. This produces thrust. All the plane needs now is lift. To achieve that, the wings and cabin of the aircraft are aerodynamically shaped so that the air coming toward the aircraft is "planed" underneath the wings. We have liftoff.
Jets account for about 7 percent of the world's petroleum use, making them one of the biggest air polluters in terms of carbon output. If you are concerned about air pollution, you can minimize your carbon footprint by seeking out other forms of transportation when feasible. Some of the more disastrous risks of jet engine flight include rotary part breakage--when pieces of the compressor come apart and ignite fuel lines--and bird strikes. Both of these risks have been radically reduced in recent decades due to design improvements and redundant engine parts.
Two of the most common makes of commercial airliners are Airbus and Boeing. The Airbus A319, A320 and A321 are standard-sized jets, seating fewer than 200 passengers. Similarly, the Boeing 737 and 757 are the standard domestic aircraft for that make. If you are flying internationally, the jet will likely be larger, such as the Airbus A330 and Boeing 767, which both seat over 200 passengers apiece. These are just two of the most common makes of commercial jetliners, but they represent the average.
