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free streamline
free streamline One passing well away from moving
body. Streamline separating fluid in motion from fluid at
rest.
free-stream Mach number Mach number of body
measured in free stream, unaccelerated by body’s
presence.
free-stream velocity Usually means difference between
body’s velocity and undisturbed air, symbol Vα.
freestyle Aerobatic routine selected by pilot, not preset.
Similarly * skydiving, not following a preset sequence.
free takeoff From aircraft carrier, not using catapult.
free turbine One that drives output shaft to propeller or
helicopter rotors, and is not connected to compressor.
free-vortex compressor Axial compressor designed to
impart tangential velocities inversely proportional
to radius from axis.
free-vortex flow Persisting in fluid remote from source
or solid surface, eg tornado.
freewheel Sprag clutch or other device which permits
helicopter rotor system to continue to rotate even if input
shaft from main gearbox is arrested.
freewing Wing freely able to rotate about spanwise axis,
thus having incidence determined by relative wind while
AOA remains constant [the reverse of conventional aeroplane].
freeze 1 To arrest dynamic operations, eg in simulator
training.
2 Radar mode which, once commanded, permits one
more scan; emissions then cease and display remains
active but frozen until * button is pushed a second time.
3 See freezing.
freeze-out Method of controlling humidity by
condensing water vapour, and possibly carbon dioxide,
over cold surface.
freezing 1 Stage in design when all major features are
irrevocably settled, thus enabling detail design to start.
2 Manually arresting input to display, leaving static
(prior) situation for study.
3 Sudden locking of flight-control system, preventing
movement.
4 Sudden onset of panic causing pilot [usually pupil] to
‘lock solid’ on flight controls, possibly with abnormal
strength.
free zone Customs-free area.
freight Cargo, including mail and unaccompanied
baggage but excluding express.
freight consolidating Process of receiving shipments of
less than carload/truckload size and assembling them into
carload/truckload lots for onward movement to ultimate
consignee or break-bulk point.
freight container See container.
freight doors Designed to take freight, vehicles or
containers.
French landing With plenty of power on.
Frensor Freezing-point sensor.
Freon Trade name for family of halogenated hydrocarbons
containing one or more fluorine atoms, including
CFCs, widely used as refrigerant medium (eg in vapourcycle
air conditioning), as fire extinguishant and as
aerosol propellant.
freq, FREQ Frequency.
frequency 1 Reciprocal of primitive period of timeperiodic
function, symbol f, units (SI) Hz, (fps units)
cycles per second.
frequency response
2 Number of services operated by airline per day or per
week over particular route.
frequency agility The ability to generate an output
whose frequency is variable. This is a basic ECCM technique.
In the case of radars the magnetron or other
waveform generator can be tuned to give a different
frequency on each scan. There are many other FA
methods for communications and other emissions. The
objective is invariably to prevent hostile jamming.
frequency band Continuous range of frequencies
extending between two limiting values; EM bands are
listed in Appendix 2.
frequency bias Constant frequency added to signal to
prevent its frequency falling to zero.
frequency channel 1 Band of frequencies which must be
handled by carrier system to transmit specific quantity of
information.
2 Band of frequencies within which station must maintain
modulated carrier frequency to prevent interference
with stations on adjacent channels.
3 Any telecommunications circuit over which telephone,
telegraph or other signals may be sent.
frequency departure Variation of carrier frequency or
centre frequency from assigned value.
frequency deviation 1 Maximum difference between
IF (1) of FM wave and frequency of carrier.
2 In CW or AM transmission, variation of carrier
frequency from assigned value.
frequency distortion Produced by unequal amplification
of signals or reproduction of sounds of different
frequency; usual criterion for high-fidelity reproduction is
level amplification over 20-15,000 Hz.
frequency division multiplex Telecommunications
allowing two or more signals to travel on one network
simultaneously by modulating separate subcarriers, suitably
spaced in frequency to prevent interference.
frequency drift Slow change in frequency of oscillator or
transmitter with time.
frequency equation Relates phase speed to wavelength
and to physical parameters of system in linear oscillation;
also known as dispersion equation.
frequency hopping Unpredictable continual and rapid
changes of frequency of radar or other military electronics
to defeat hostile ECM.
frequency modulated radar One in which range is
measured by interference beat frequencies between transmitted
and received FM waves.
frequency modulation, FM Instantaneous frequency of
modulated wave differs from carrier by amount proportional
to instantaneous value of modulating wave.
Combination of phase and frequency modulation
commonly referred to as FM.
frequency monitor Stabilized receiver giving audible or
visual indication of any departure of transmitter from
assigned frequency.
frequency pairing Association of each VOR frequency
with a specific DME channel to reduce workload and
errors.
frequency parameter Ratio of airspeed to product of
frequency of oscillation and representative length of oscillating
system.
frequency response 1 Portion of EM spectrum sensed
within specified limits of error.
2 Response as function of excitation frequency.
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