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Noise-generating aircraft propeller. Aircraft noise is noise pollution produced by an aircraft or its components, whether on the ground while parked such as auxiliary power units, while taxiing, on run-up from propeller and jet exhaust, during takeoff, underneath and lateral to departure and arrival paths, over-flying while en route, or during landing.
The primary sources of jet noise for a high-speed air jet (meaning when the exhaust velocity exceeds about 100 m/s; 360 km/h; 225 mph) are "jet mixing noise" and, for supersonic flow, shock associated noise. Acoustic sources within the "jet pipe" also contribute to the noise, mainly at lower speeds, which include combustion noise, and sounds ...
This gives a less effective exhaust gas velocity (lower jet noise) and therefore lower efficiency, and can be achieved in the landing phase by using a variable area final nozzle to rematch the fan. Furthermore, acoustic treatment in the intake and exhaust ducting can minimize turbomachinery noise.
A hush kit is an aerodynamic device used to help reduce the noise produced by older aircraft jet engines. These devices are typically installed on older turbojet and low-bypass turbofan engines, as they are much louder than later high-bypass turbofan engines .
The FAA Stage 5 noise standards are equivalent. [49] Higher bypass ratio engines produce less noise. The PW1000G is presented as 75% quieter than previous engines. [50] Serrated edges or 'chevrons' on the back of the nacelle reduce noise. [51] A Continuous Descent Approach (CDA) is quieter as less noise is produced while the engines are near ...
As in the case of roadway noise, little progress has been made in quelling aircraft noise at the source, other than elimination of loud engine designs from the 1960s and earlier. Because of its velocity and volume, jet turbine engine exhaust noise defies reduction by any simple means.
Acoustic quieting is the process of making machinery quieter by damping vibrations to prevent them from reaching an observer. Machinery vibrates, causing sound waves in air, hydroacoustic waves in water, and mechanical stresses in solid matter.
The earliest-known implementation of a Hoerner-style downward-angled "wingtip device" on a jet aircraft was during World War II. This was the so-called "Lippisch-Ohren" (Lippisch-ears), allegedly attributed to the Messerschmitt Me 163 's designer Alexander Lippisch , and first added to the M3 and M4 third and fourth prototypes of the Heinkel He ...