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efractive index radar
radio/radar important forms are atmospheric * (lowaltitude
temperature, pressure, humidity; also responsible
for errors in apparent altitude of celestial bodies), coastal
* (change in propagation path at land/sea boundary) and
ionospheric * (change of direction in passage through
ionized layer).
refractive index Ratio of phase velocity of EM radiation
in free space (vacuum) to phase velocity in medium
considered; normally related to air, though in fact ** for
air is not unity, common S/L value being 1.003. For radio
normally refined to modified ** (n + h/a) where n is ** at
height h and a is radius of Earth.
refractory Resistant to high temperatures; normally
implies able to retain precise structural shape and bear
appreciable stress at temperatures up to 2,200° C
(4,000°F) without significant long-term change.
refresh rate Rate at which data on electronic display, eg
radar, are resupplied in order to maintain bright picture
free from flicker; early radar had no refresh and picture
was generated only once on each scan; today data are
updated at each revolution but are refreshed 100 to 200
times between updates. Panel-instrument * is usually
40–80 Hz.
refrigerant Working fluid pumped round closed circuit
to extract heat, usually by repeated evaporation/
condensation.
Refrigerant 12 Difluorodichloromethane (DDM).
refrigerant injection Water injection into gas turbine.
refrigeration capacity Common unit is ‘tons’, normally
a heat-extraction rate sufficient to convert one short ton
of water at 0°C to ice every 24 h, equivalent to 3.517 kW
= 4.715 hp.
refrigeration icing Caused by sudden drop in temperature
of airflow, notably by depression in choke tube
and/or evaporation of fuel.
refrigeration tunnel Wind tunnel used for icing tests.
REFS Reconfigurable engineering flight simulator.
refusal speed That at which a takeoff can no longer be
aborted, equivalent to V 1 (RAF).
REG 1 Registration, registered.
2 Regular.
3 Regulation.
Rega, REGA Swiss air ambulance association. Not an
acronym, but French and Italian counterparts GASS are.
Regal Range and elevation guidance for approach and
landing (FAA test 1960).
regard Total solid angle of ‘vision’ of a sensor trainable
to point in different directions; FOV may be much less.
regeneration 1 Introduction of closed-circuit operation
in gas-turbine plant in which by various methods part of
exhaust heat is extracted and used to increase temperature
of incoming airflow; hence regenerative gas turbine.
Essentially synonymous with use of heat exchanger.
2 Increase in radio detector sensitivity by positive feedback.
3 Favourable heat transfer between rocket thrust
chamber nozzle and propellant (see regenerative cooling).
4 In EDP (1) rewriting to prevent memory
deterioration.
regenerative cooling Use of a cool incoming liquid, eg
rocket-engine propellant, to remove heat from hot hardware,
eg rocket nozzle skirt and exit cone. Essential
feature is that heat transfer is beneficial to both cooled
item and coolant.
reinforced carbon/carbon
regenerator See heat exchanger.
RegFD Regulation fair disclosure (US Securities and
Exchange Commission).
regime One defined mode of operation, clearly distinguished
from other types of operation of same device; eg
USAF fighter flight-suit pressure regulator has lo * maintaining
3 lb/sq in and hi * maintaining 6.5.
region See flight information region.
regional airport One serving a number of (usually
modest-sized) local communities.
Regional augmentation Navsat transponders broadcast
ground-derived GPS integrity assurance and accuracy
enhancement.
regional carrier Civil operator whose route network
covers only a minor part of a large country, and not over
500 nm sectors; often same as third-level. In the US, a
traditional definition included “an operator whose
aircraft do not exceed c70 seats.”
regional QNH See QNH.
register Small array of bistable circuits storing one EDP
(1) word.
registering balloon Small free balloon carrying
recording meteorological instruments; ballonsonde.
registration Entry of civil aircraft into records of
national certification authority, with allocation of
letter/number code displayed on aircraft [Appendix 9] and
* certificate which in most countries must be displayed
inside aircraft.
REGL Regional.
REGR Recent hail.
regression Precession of nodes; eg Moon completes
revolution in 18.6 years.
regression rate Linear rate at which solid-propellant
grain burns, measured normal to local surface; in 1970
typically 0.25 mm/s, in 2002 over 5 mm/s.
regressive burning Solid-motor combustion in which
burn surface area and hence chamber pressure and thrust
all fall throughout period of burn.
regressive orbit See retrograde.
regroup airfield Military or civil airfield at which post-
H-hour, aircraft would reassemble for rearming,
refuelling and resumption of armed alert, overseas
deployment or further combat missions (DoD, IADB).
REGS Regulations.
regular airfield One which may be listed in flight plan as
intended destination.
regular airport That at which scheduled service calls
(UK usage).
regulated take-off weight See WAT-limited.
REH Rapid-erect hangar.
reheat Original [UK] term for afterburning.
REHM Recording engine health monitor.
REI 1 Repair engineering instruction.
2 Reusable external insulation
Reid vapour pressure Absolute pressure of liquid
[usually hydrocarbon fuel] in enclosed volume at given
temperature, usually 100°F (37.8C).
REIL Runway-end identification or identifier lights
(FAA); S adds system.
reinforced carbon/carbon Composite material
comprising high-strength carbon fibres bonded in matrix
of pyrolitic carbon; or can be thought of as pyrolitic
carbon reinforced with CF.
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