If you have ever lived near an airport, you know that an airport generates a tremendous amount of noise. Of course it is the aircraft that generates these noises and it is aircraft that are, in many ways, responsible for the variety of problems associated with these high noise levels. To understand the problem of aircraft noise, it is important to understand exactly what it is that causes airplanes to make so much noise.
If you want to understand what causes airplanes to make so much noise, you need to understand a little bit about an aircraft engine. An aircraft engine includes, among other things, a fan which is located toward the front of the engine and the propulsive jet, which is near the rear of the engine. The jet is the thing that actually makes the aircraft move. The engine of an aircraft is the primary source of noise. The sound of the fan creates noise as it spins and this is the whirring that you can hear when you are in an airplane and you are getting ready to taxi down the runway to take off. The other half of the engine noise is created by the propulsive jet. This is the sound of the gases as they escape from the jet and as they push the plane forward.
There is another source of noise, however, for an aircraft. When an aircraft is approaching an airport, the aircraft makes just as much noise as the engine itself. This is because air flows over the flaps, the undercarriage, and the slats on an aircraft. As the air flows past these obstacles, the air is unsteady and this causes the frame of the jet to create sound.
Fortunately, there are some ways to reduce the noise that an aircraft makes. For example, engineers have created specific types of shielding that will make the airplane engine quieter. Another important component in reducing airplane noise is moving the engines above the wings. When the engines are beneath the wings, sound tends to reflex downward toward the ground. When the engines are above the wings, the noises that the engines produce are shielded from listeners that are on the ground. A number of other technologies such as acoustic liners located in the inlet of the engine and the exit ducts of the engine can help to absorb some of the engine noise. In addition, air frame noise can be cut by slowing the approach speed when the plane is preparing to land. In addition to reducing sound this provides a number of other benefits to the flight process.
