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nodding
nodding Deflection under vertical acceleration of masses
cantilevered ahead of or behind main structure, eg
forward fuselage (in flight only) or engine on wing pylon
well ahead of leading edge.
nodding aerial One oscillating only, or principally, in
vertical plane, eg HFR.
noddy cap Protective cover for delicate (eg IR-homing)
missile nose (RAF, colloq.).
NODE National operational [ATC] display equipment.
node 1 In structures, location of point where load variation
causes only rotation but no linear deflection.
2 Point, line or surface in wave system where some
major variable has zero amplitude.
3 In any network, terminal point or point where two
channels branch.
4 Intersection of orbit of satellite with plane of orbit of
primary.
5 Location in mobility system where movement is
originated, processed or terminated (DoD).
NODLOR Night observation device, long-range.
no-draft forging One forged essentially to finish dimensions,
thus needing little if any machining.
NODS 1 Night observation and detection system.
2 Near-object detection sensor.
nodular cast iron See SG cast iron.
NOE Nap of the Earth, ie flight as low as posible over
undulating terrain.
noed Knot (F).
no-escape zone In AAM engagement with fast target,
often less than 0.25 maximum AAM range.
NOF International Notam Office (ICAO).
no-feathering axis Axis of swashplate, about which there
is no feathering moment or first-harmonic variation of
cyclic pitch.
no-feathering plane That in which an observer sees no
variation in cyclic pitch [helicoper rotor].
no-flare landing Aeroplane landing (rarely, other
aircraft) in which approach trajectory is continued in
essentially straight line until landing gear hits ground.
no-fly list Passengers who, for whatever reason, are
permanently denied boarding (TSA).
no-fly zone Airspace prohibited to the aircraft of that
country, and [usually] patrolled by aircraft of a hostile
country to ensure compliance.
NOFORN No foreign [dissemination of information]
(US).
Nogaps Navy operational global atmospheric prediction
system (USN).
no-go gauge One whose linear dimension (between
faces, threads or diameter) is just below smallest permitted
limit for part.
no-go item One whose failure or absence from aircraft
prohibits takeoff according to operating rules (though not
necessarily rendering it unairworthy).
NOGS, Nogs Night observation gunship system.
NOI 1 Notice of intention.
2 Notice of Inquiry (US).
3 NCCT operations interface.
NOISE National Organization to Insure [sic] a Soundcontrolled
Environment (US).
noise 1 Noise in air. Basic unit is decibel, dB, 0.1 bel,
measure of sound pressure above local atmosphere on
logarithmic scale, usually related to starting reference
pressure of 2 × 10 –5 Nm –2 . Sound pressure level L = 10 log
noise
p 2 /p o 2 = 20 log (p/p o ) where p o is reference pressure and p
actual measured pressure. Alternative is to use source
power level L W = 10 log (W/W o ) dB where W o is reference
power commonly taken to be 10 –12 W (Watts). Pressure
levels are more common, and log scale allows for millionfold
increase in human perceived pressures, each 6 dB
increment representing doubling of pressure level. Study
of aircraft noise from 1952 led to many new measures in
attempts to quantify noise nuisance. In 1953 CNR
(Community Noise Rating) gave single-number scale
based on public response to six generally quantifiable
factors, and in 1957 NC (Noise Criteria) curves attempted
to portray equal-loudness contours taking into account
discrete tones, impulsive nature of some sounds and other
variables. By this time many workers had tried to quantify
human aural response to different frequencies and
tones with mixed frequencies, and curves drawn in 1959
were labelled L PN (Perceived Noise Level) in units of
dB(PN), sometimes written PNdB. Despite its complexity
this gained major foothold, and virtually eliminated
traditional measures (phon, relating sound pressure level
to standard 1 kHz tone, and sone, loudness corresponding
to 40 phons). Various weighted dB measures were introduced
for the measures taken by meters with scales
adjusted to equal-loudness contours for different overall
pressure levels, these being called by various letters (thus,
A-weighted = dBA = L A ). In 1961 a series of surveys
measured annoyance according to new measures, L PN50 or
L PN90 (L PN exceeded by 50 or 90 per cent of aircraft), D 85
or D 95 (10 log time in seconds when sound pressure
exceeded 85 or 95 dB), and N (number of aircraft ‘passing
over’, latter criterion not being defined); result was single
value for location called NNI (Noise and Number Index).
Another 1961 unit was derived by splitting noise into onethird-octave
bands and assigning each band a Noy rating
by comparing with subjective noisiness of random noise
centred on 1 kHz; individual Noy figures then added by
method allowing for masking of one band by others and
presented in PNdB. Further work allowing for particular
features – such as intense pure tones, as from compressor
blading, in otherwise broadband jet sound – led to use of
L EPN (Effective Perceived Noise Level) measured in
EPNdB (Effective Perceived Noise dB) in first-draft legislation
in 1966, which led to FAR Pt 36 and subsequently
closely similar ICAO Annex 16. By that time at least 20
national or local authorities had published research,
including Australia’s AI (Annoyance Index) = L – PN + 10
log N; German Störindex Q – based on dBA; French R-
index = L – PN + 10 log N-30; Dutch Total Noise Rating B
based on log of summation of A-weighted pressure levels;
American CNR (Community Noise Rating) based on
many variables; California’s CNEL (Community Noise
Equivalent Level) using WECPNLs (Weighted
Equivalent Continuous Perceived Noise Levels) varying
with time of day and season; American NEF (Noise
Exposure Forecast) = L – EPN + 10 log N-K where K is 88
by day and 76 by night; the European Community’s
L DEN = noise from all sources [noise density] summed
through each 24 h; South Africa’s NI (Noisiness Index) =
L – × 10 log N + 10 log T a /T where T a and T are times;
British TNI (Traffic Noise Index) and resulting L eq
(Equivalent Average Sound Pressure Level), which led to
L NP (Noise Pollution Level) = L eq + 2.56 σ where σ is standard
deviation of dB fluctuations. Further measures
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