Aircraft Noise - Research Paper Example

Running head: Aircraft Noise Name: University: Course: Tutor: Date of Submission: Introduction Aircraft noise is one type of noise pollution which is usually produced by aircrafts as well as its components during various phases of the flight. The identified phases through which an aircraft produces noise to the environment consists of; when the aircraft is parked on the ground, while taxiing, on run-up from propeller and jet exhaust, during takeoff, underneath and lateral to departure, when landing and while over-flying (Smith,56-60). Aircraft noise actually is a major problem facing many of the communities living around airports as well as those living near under flight paths especially during the night (Woodward, & Briscoe,20-45).Not only does the noise problem have a strong impact on communities living around airports as well as along under- flight paths it also has a strong effect on passengers, cabin crews and even the pilots too. Aircraft noise therefore has been issue since the introduction of first jet aircraft and the problem has been made worse through progressive technological developments, flights frequent movements as well as introduction of larger aircrafts which produce much noise (Austin, 114-120). Aircraft noise is very much disruptive especially to individual living around the airports, though the effects associated with it are not uniform around the whole world rather it differs according to the types of aircrafts operating at a particular airport, the location, type of housing under the flight path, airport hours of operation as well as the total number of flights that the airport has (Moir, & Seabridge, 30-40). The health effects associated with aircraft noise consists of hearing impairment, hypertension, heart diseases, sleep disturbances and decreased school performance. Aircraft noise A study done by (O'Connell, 12-30), indicate that aircraft noise is a result of an interaction between the aircraft components as well as the air molecules. A moving aircraft causes compression and rarefaction to occur in the air, a process which in turn results to air molecules movement. The air molecules movement in turn propagates through the air as pressure waves creating an audible frequency spectrum that produces sensational hearing known as noise (O'Connell, 12-30). Aircraft noise therefore can be viewed as a result of the interaction between the aircraft and moving air molecules. A research study by Woodward, & Briscoe,20-45),shows that various kinds of aircrafts tend have different noise levels and frequencies hence the three main sources of aircraft noise consists of; Aerodynamic noise, Engine and other mechanical noise and Noise from aircraft systems (Woodward, & Briscoe,20-45). Aerodynamic noise of the aircraft Aerodynamic noise is the kind of noise which arises from the flow of air around the aircraft fuselage and its control surfaces. This kind of noise is usually generated as a result of unsteady motion of the air and its interaction with the surrounding aircrafts control surfaces sometimes referred to as aerodynamically generated sound (Smith, 56-60). Aerodynamic noise is unpleasant to human ears and in most cases the noise is usually produced when an aircraft is landing and taking off from the ground. In other cases aerodynamic noise in aircrafts comes as a result of descending and forward flight movements of a helicopter. On other hand Jet-powered, low-flying and high- speed military aircraft produce intense aerodynamic noise from its aerodynamics. This kind of noise tends to increase with aircraft speed as well as when the flight is flying at low attitudes due to the density of the air. A study done by(Woodward, & Briscoe, 20-45), indicates that the different shapes of an aircraft nose, windshield and canopy determine the kind of Aerodynamic noise produced from a certain aircraft (Woodward, & Briscoe, 20-45).From the research it was evident that much of the aerodynamic noise produced is from the aircraft propellers and airscrews. This is because of the constant flow of the air around the blades. When an aircraft is moving Aircraft propellers which usually are attached to the crankshaft of a piston engine and airscrews convert rotary motion generated from piston engines as well as turboprops into propulsive force (Crocker, 10-35). In the case of helicopters main and tail rooters are key sources of aerodynamic noise hence this kind of noise is usually of low frequency given the fact that it normally determined by the rotor speed. Research done by (Crocker, 10-35), indicates that aerodynamic noise in a helicopter is usually generated when air flow passes aircraft objects such as wings or landing gears and its surfaces. Research survey done by Crocker (10-35),show that there two types of aerodynamic noise and they comprises of; Bluff Body Noise which is normally produced from alternating vortex shedding from either side of an aircraft bluff body. When this happen low pressure region are created at the core of the shed vortices which eventually manifests themselves as pressure waves normally referred to as aerodynamic noise. The aerodynamic noise is usually caused by unstable air flow around the bluff body of the aircraft (Crocker, 10-35).During the process the airflow rolls up into ring vortices which eventually break down into turbulence releasing noise to the surrounding environment. The second type of aerodynamic noise is Edge Noise. This kind of noise is usually produced when a turbulent flow passes near aircraft control surfaces as well as through high lift aircraft clearance devices. When this happens fluctuations in pressure occurs producing unpleasant sound to the surrounding environment normally referred to as aircraft noise. Engine and other mechanical noise Aircraft Gas Turbine engines normally refereed to as (Jet Engines) are perceived to be accountable for much of the aircraft noise especially when the aircraft is taking off as well as when it is climbing .The advances in noise reduction technology has reduced the noise produced from the jet engines hence today airframes are more noisy especially during landing. This kind of noise normally is a by product of the turbulent exhaust air mixing relatively with calm surrounding ambient air (Crocker, 10-35). This usually occurs as a result of high velocity being producing from a jet engine nozzle which eventually causes low turbulence airflow .This airflow in turn produces a low frequency noise which does not travel very far though as the gases are dissipated further from the nozzle the turbulence increases and interacts with the air causing a high frequency sound which eventually reaches the human ear as noise. Noise levels from various engines vary but they are directly proportional to the engine thrust as well as the amount of work the engine performs on the air while passing through the air. This implies that larger engines can move the same amount of air as a smaller engine does though thrust produced is the same (Woodward, & Briscoe,20-45). Turbofans are quieter than turbojets at equivalent thrust outputs because of the way a turbofan processes air. Turbofans have larger turbine which normally supply the necessary power to drive fan hence reducing velocity of the exhaust as well as aircraft noise. Noise from aircraft systems Studies show that Cockpit and cabin pressurization as well as aircraft conditioning systems are major contributor’s aircraft noise. From the research conducted it was clear that the most significant source of cabin noise especially from a commercial jet aircraft apart from engines is Auxiliary Power Unit (APU). Cabin noise To begin with, the first way through which the noise is usually produced in the cabin is through the combination of turbulence in the boundary layer located on the outer surface of the cabin and the engine noise which is usually transmitted through the atmosphere as vibration via the airframe structures (Crocker, 10-35). Cabin noise too is usually released from internal aircraft systems in particular the cabin air conditioning/pressurization system and there associated ducting. The worst cabins are those of the helicopter and propeller powered aircraft in which noise from the rotors is extremely difficult to control. Auxiliary power units (APUS) An Auxiliary Power Unit is an on board power generator installed in an aircraft and primarily is usually used to start the main engines using compressed air as well as provide electrical power to the aircraft when it is on the ground. These units supply essential power to the aircrafts while they are on the ground at the airport as well as when the main engines are not working or in situations where no external power supply is available (Crocker, 10-35). The Auxiliary power units are small gas turbine engines mounted in the rear of the fuselage that in normal circumstances provides an audible source of noise to passengers and cabin crews when the craft is being prepared to take off. The noise produced from these components has no effect on the communities living around the airport rather is of a major concern to ground crew. Air and hydraulic power systems These systems are of no consequence in the overall airport noise scene rather the noise produced from them can be of high effect to the passengers and cabin crews. Although the noise suppressors have been developed primarily to reduce the level of low frequency noise to given level of degree, their benefits is only to minimize shock noise by disturbing the shock structure in the supercritical jet. The increase in noise mixing rate do enlarge the cone of silence raising frequency of spectrum of mixing noise. This entire process causes some noise disturbance to the passengers (Crocker, 10-35). Cockpit noise The other source of internal aircraft noise is usually from the airflow from the cockpit conditioning as well as pressurization systems. The noise is usually generated through turbulent airflows coming from an aircraft outlet sprays. In addition cockpit noise is also generated as a result of turbulent flow around and across the canopy as well as protuberances around other areas such as IR sensors, canards, refueling probes Noise levels produced from cockpit systems are usually associated with cabin conditioning and cooling flow hence in most cases it is normally constant with speed and height (Woodward, & Briscoe, 20-45). The cockpit noise spectrum in most cases usually varies with the given conditioning mode. In the case of fast jets the internal cockpit noise spectrum is usually random in nature with high energy levels spread over abroad frequency band. Cockpit noise is usually generated from two predominant sources thus the external airflow around the aircraft canopy as well as the front structure of the aircraft. The other source is internally generated noise which is usually released from air conditioning and cooling flows which inturn travels to the cockpit space. The noise levels which are normally generated from the external airflow sources in most cases are dependent upon aircraft dynamic pressures as well as speed and height of the aircraft. Noise mitigation programs Noise mitigation programs are a set of strategies implemented to reduce aircraft noise pollution. Over the years this has been a challenge to many airports around the world hence great progress continues to be made as away of reducing aircraft noise around airports. Reverse Thrust Restrictions program Noise from the use of jet engine thrust reverse is considered to be a key source of aircraft noise at the Airport. Pilots usually use reverse thrust procedures to slow a jet aircraft for an appropriate landing as well as an appropriate measure for passengers’ safety (Smith, 79-101). Reverse thrust usually redirects the flow of the jet-engine exhaust towards the front of the aircraft hence slowing down the aircraft as well as maintaining directional control on the ground in the event of landing. The redirection of jet exhaust usually results to an increase in noise to the sides of the aircraft especially during night hours. Though, this method is safe since it ensures passengers safety as well as it is according to the stipulated landing procedures many airports should implement Reverse Thrust Restrictions program which restricts pilots from frequently using this method of landing as way of reducing noise problem when an aircraft is landing(Smith,79-101). Ground Noise Reduction programs Ground noise control programs are programs designed to reduce noise from the jet engines maintenance. An example of these programs is run-up rules restriction which restricts airport engine maintenance at night bewteen10 p.m. and 7 a.m in the morning. In case of violation by any airline a certain fee should be imposed to the airline by that particular airport. Another program which can help in reducing ground aircraft noise problem is the implementation of Gate push backs restrictions. These restrictions states will restrict aircrafts from being pushed back by a tug rather than by powering up them with jet engines. This helps in reducing jet engine noise when the plane is taking off as well as while landing. Noise monitoring programs These programs related to noise data monitoring by respective monitoring sites. Most of the Airports around the world have developed permanent regional noise monitoring sites which are responsible for tracking data, implementing the noise reduction programs as well as responding to citizen complaints and information requests about the noise (Lombardo,20-30). The noise monitoring sites are charged with the responsibility of recording community and daily aircraft noise. The monitoring sites use the recorded data to update noise contours as well as put in place required measures in reducing the levels of noise. Property Programs Property Acquisition/Relocation These are property acquisition and relocation programs in which the airport staff works in hand with residents living around the airport, property owner and tenants when their land is required for airport construction or in cases where the residential use is incompatible with airport activities (Smith,79-101). Mobile Home parks programs Since some mobile homes cannot be sufficiently sound insulated, some airports operating near such homes park should implement relocation programs for the residents living in these homes and who most of the time are affected by aircraft noise. Noise Remedy Program This is a program which has been designed to use sound insulation primarily as a way of reducing aircraft noise to the communities living around the airports. Airports should struggle to put in place these programs in addition to putting in place community resource noise mitigation information (Lombardo,14-20). This is because such programs provide guidelines on specific materials that residents living around the airport can use for roofing hence reducing interior noise levels and its effects. This program should be developed for homes as well as schools, churches, hospitals and any other buildings near the airports and under the flight runway. Single Family Home Insulation This is a program reduces the levels of noise experienced by communities living around the airport as well as to residents who have houses build on the flight runway path. Cabin noise control programs Methods of controlling cabin noise have proved to be effective when it comes to controlling internal aircraft noise. This is usually achieved through containing the noise at the source or by modifying the fuselage structure or cabin furnishings tends to reduce the performance of the aircraft by increasing the cost of operation (Eagan & Gardner, 78-90). The turbofan power plant contributes little to the cabin noise due to the mere fact that airborne noise, jet velocity and resultant mixing noise is of low frequency due to low levels of vibration from the turbine engines. The noise produced usually is of low frequency hence strongly transmitted via the airframe structures as well as the atmosphere. Conclusion Aircraft noise is one of the major challenges that various airports all over the world have been facing with many of them trying to put in place strategies and mitigation programs to control this problem. Reference Austin, Reg. Unmanned Aircraft Systems: UAVS Design, Development and Deployment. New York: John Wiley and Sons, 2010:114-120 Crocker, Malcolm J. Handbook of noise and vibration control. London: John Wiley and Sons, 2007: .pp10-35 Eagan, Mary E & Gardner, Robin. Compilation of noise programs in areas outside DNL 65.vol 16. Washington: Transportation Research Board, 2009:78-90 Lombardo, David A. Aircraft systems. Chicago.2nd ed. McGraw-Hill Professional, 1998:pp14-20 Lombardo, David A. Advanced Aircraft Systems. Chicago.2nd ed. McGraw-Hill Professional, 2008:pp20-30 Moir, Ian & Seabridge, Allan. Aircraft systems: mechanical, electrical, and avionics subsystems Integration.3ed.New York: John Wiley and Sons, 2008:pp.30-40 O'Connell, Max H. Aircraft noise. Michigan: School of Aviation Medicine, USAF Aerospace Medical Center (ATC), 2006:12-30 Smith, Michael J. T. Aircraft noise.vol 3. New York: Cambridge University Press, 2004:56-60 Smith, Michael J. T. Mitigation programs to Aircraft noise, vol 3.New York: Cambridge University Press, 2004:79-101 Woodward, John M & Briscoe, Lisa L. Aircraft noise: a toolkit for managing community Expectations, Volume 15.Publisher: Transportation Research Board, 2009:20-45 Read More