ENVI ENG Flashcards
is any undesirable or unwanted sound.
Noise
The first-generation jet aircraft in the _____ led to a rapid expansion in commercial aviation and their engines created significant noise.
1950s
In the 1970s, the U.S. ________________ introduced the first noise certification standards
and the ________________ promoted similar standards
globally (Smith, 1989).
Federal Aviation Administration (FAA) ; International Civil Aviation Organization (ICAO)
Chapter 2 of ICAO’s “Environmental Protection/ Annex 16 to the Convention on International Civil Aviation” (ICAO, 2008a) defined ____________
for aircraft certified before October 6, 1977 (with some exemptions);
noise standards
Sound level is measured in _______
decibels
Two General Sources of noise from aircraft
Engines and the Airframe
Aircraft generate noise whenever there is_____________________________.
high-speed or turbulent airflow and/or high-speed mechanical movement and rotation
Airframe noise is caused by the __________________________________.
flow of air over the surfaces of the aircraft and the turbulent flows created by the structure and cavities introduced by the deployment of high-lift devices and landing gear
Engine noise tends to dominate on the ground, especially during _________ when
the engines are at very high thrust level, on _______ when using thrust reversers and
when taxiing at low speed.
takeoff ; landing
Another source of aircraft noise besides the engine and airframe
Sonic Boom
sonic boom created by aircraft flying at ___________ which can be very
disruptive to activities on the ground.
supersonic speeds
The increasingly stringent _______________ have spurred the development of low-noise technologies for new aircraft.
noise certification standards
Most reductions in aircraft noise have
been achieved through improvements in _________
engine technology
the ratio between the amount of air drawn in by the fan that bypasses the engine core relative
to that passing through the core.
Bypass Ratio
Bypass Ratio of Large modem turbofan
10:1
Sound Energy radiated by such sources is
transmitted through the air in sound waves which are tiny pressure fluctuations just
above and below atmospheric pressure.
These pressure fluctuations, called _______ , impinge on the ear, creating audible sound.
sound pressures
root-mean-square (RMS) value that is the square root of the average squared pressure fluctuation over some brief period of time
Sound Pressures
The loudest sounds people can hear without pain have about __________ the RMS sound pressure as the faintest sounds people can hear.
1 million times
Equally remarkable
is the way the auditory system perceives _________ in loudness.
changes
The smallest difference in RMS sound
pressure the human auditory system can detect is about ________.
10 percent
____________, is well suited for quantifying
sound in a manner which relates to human perception.
a logarithmic, or decibel scale
In its logarithmic form, RMS
sound pressure is called the _________
RMS sound pressure level (SPL).
is the logarithm of the ratio of two squared pressures, the numerator containing the
pressure of the sound source of interest and the denominator containing a reference
pressure
Sound Pressure Level
The unit of sound pressure level
decibels
Another important attribute of sound is its ___________.
frequency, or pitch
unit of frequency
hertz
this is the number of times per second the sound pressure oscillates back and forth
about atmospheric pressure
Pure tone
The normal frequency range of hearing for a young adult extends from a low of
__________________.
16 Hz to a high of about 16,000 Hz
