Aviation noise Guide, Meaning , Facts, Information and Description
Aviation noise is one of the most publicised forms of environmental noise.Sound will always be produced by aeroplanes. As an aircraft moves through the atmosphere, compression and rarefaction of the air will produce motion in the air molecules. Similarly, an aircraft jet engine or propeller will also cause movement in the molecules of the atmosphere. This movement in the air molecules propagates through the air as pressure waves. If these pressure waves are strong enough and within a certain frequency spectrum, it produces a sensation of hearing. Noise can simply be defined as unwanted sound. There are few aircraft, if any, where the question of unwanted sound, or noise, does not arise.
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2 External noise of civilian aircraft activity |
Different aircraft types have different noise levels and spectra. The contributions to the total noise levels originate from 3 main sources:
Cockpit and cabin noise
Historically, cockpit noise levels have always been high, and the development of new aircraft and operation types have not necessarily led to improvements over the years. Aerodynamic noise
Aerodynamic noise arises from the external airflow around the aircraft fuselage and control surfaces. This type of noise increases with aircraft speed and also at low altitudes due to the density of the air.
Jet-powered aircraft noise has a large aerodynamic contribution and is typically broad-band. Low-level, high-speed flight in military combat aircraft carries a particularly large aerodynamic noise contribution.
The level of aerodynamic noise varies with aircraft design. Thus, the shape of the nose, windshield or canopy of an aircraft can greatly affect the noise level.
Much of the noise of a propeller-driven aircraft is aerodynamic noise due to the flow of air around the propeller blades. The helicopter main and tail rotors also give rise to aerodynamic noise. This type of aerodynamic noise is mostly low-frequency and is related to the rotation speed of the propeller or rotor.
Aviation noise may cause problems in communities and has been claimed to cause several types of health problems. It is said to cause heart diseases, immune deficiencies, neurodermatis, asthma and other stress related diseases. Allthough there are some studies that suggest connections with disease, further research needs to be carried out to increase knowledge in this issue.
Since aviation noise became a major public issue in the 1960s and 1970s, governments around the world have brought in legislative controls, and aircraft designers, manufacturers, and operators have developed quieter aircraft and more careful operating procedures. Modern fan-jet engines, for example, are quieter than the pure jets of the 1960s. This is an Article on Aviation noise. Page Contains Information, Facts Details or Explanation Guide About Aviation noise Engine and other mechanical noise
Engine noise contributes to the general noise level in an aircraft. However, much of the noise in propeller-driven aircraft comes from the propellers themselves and as such is aerodynamic noise. The highest levels of internal aircraft noise usually found in line with the propeller blades.
Helicopter noise has a unique spectral content, essentially being aerodynamically induced noise from the main and tail rotors and mechanically induced noise from the main gearbox and various transmission chains 3 . The mechanical sources produce narrow-band high-intensity peaks relating to the rotational speed and movement of the different moving parts. Noise from aircraft systems
Internal aircraft systems also form an important part of the noise in aircraft of today. Cockpit and cabin pressurisation and conditioning systems are often a major contributor to noise in both civilian and military jet aircraft. Other internal aircraft systems can also contribute, such as specialised electronic equipment in some military aircraft.External noise of civilian aircraft activity
Starts, approach and landing of aircraft may lead to a noise of more than 100 dB(A) at the ground.
Since aircraft landing in inner-city airports are often lower than 200 ft (60 m) above roof level, they can cause a noise of more than 95 dB(A).