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variable-geometry inlet
reasonable efficiency it is essential to have not only fully
variable inlet and nozzle but also variation in flow path in
engine itself, eg to divert flow around HP compressor in
supersonic mode or to convert engine into ramjet. Needs
explanation when used.
variable-geometry inlet See variable inlet.
variable-incidence Pivotally mounted so that angle of
incidence can be altered. * guide vane, stator blade or
turbine inlet guide vane whose incidence is altered for best
compromise between flow incident on leading edge and
flow angle leaving trailing edge, invariably auto scheduled
by engine control system. * tails, tailplane whose incidence
is varied either for trimming, with elevators as
primary flight control surfaces, or as primary flight
control. * wing: wing pivoted on transverse axis so that
over full (large) range of flight AOA fuselage can remain
more or less level, eg to improve pilot view on approach
or permit short landing gear.
variable inlet Variable-geometry airbreathing engine
inlet whose area, lip/wedge/centrebody axial position and
duct profile can all be adjusted to match required flight
shock position and mass flow. Mere downstream auxiliary
inlets or spill doors do not qualify.
variable-inlet guide vane Gas-turbine IGV whose incidence
varies according to engine operating regime; very
rare upstream of turbine but common upstream of first
and often subsequent stages of axial compressor, to match
airflow mass flow and whirl to rotor blade conditions and
avoid stall; controlled by auto system always sensitive to
rotor speed and inlet air temperature and occasionally
to other variables.
variable load All variables aboard aircraft other than
fuel and payload.
variable metering orifice In gas-turbine fuel system, key
element in CASC comprising triangular orifice moved
axially by stack of aneroid capsules and part-covered by
sleeve moved by centrifugal SCG.
variable overhead Varies with number of particular item
manufactured.
variable-pitch Synonymous with variable incidence.
Normally confined to propellers, where incidence is called
pitch. Usually means pitch can be varied on ground, or by
pilot in flight, often only as choice of either coarse or fine
pitch, without auto control such as constant-speed. Fine
distinction between * and adjustable-pitch, latter explicitly
meaning ground-adjustable only.
variable-ratio Two main applications: in shaft-drive
gearbox * drive is usually synonymous with constantspeed
drive, ie ratio is varied to hold output speed
constant despite varying input; * bypass engine or
turbofan (rare) has bleeds, two-position shutters or doors
to change ratio of airflow between bypass duct and core.
variable-stability aircraft Aircraft, invariably aeroplane,
whose flight-control surfaces, and possibly structure, can
be acted upon in flight to effect gross change of stability
and control characteristics, either for research or to mimic
the behaviour of a totally different type. The inputs
should be seamless, not noticed by pilot.
variable-stator Usually means gas turbine with not just
one but several rows of variable-incidence stator blades
(vanes) in axial compressor(s). These are required to avoid
surge and/or blade stall.
variable-stroke Though many reciprocating engines and
machines patented with *, invariably means axial oscillating
plunger liquid pump driven by variable-angle
swashplate (see variable-delivery).
variable-sweep Aerofoil is pivoted so that sweep angle
can be varied. Mainly applicable to main wings, where
left/right wings are made separate from rest of structure
and attached by large diameter fatigue-free pivots so that
both surfaces can be scheduled (either auto or by pilot
command) by actuator over wide range of sweep angles,
symmetrical about axis of symmetry. Does not mean slewwing.
(Helicopter blade rotation about drag hinge is
strictly * but is not called such). Also called variablegeometry
(VG) and (colloq.) swing-wing.
variable-timing Feature of magneto drives enabling ignition
to be advanced or retarded [there are many other
aerospace meanings].
variance Mathematical average of square of deviations
from mean value.
variance rate Difference between standard and actual
wages (US hourly-paid workers).
variant Different version of same basic aircraft type.
variation 1 Horizontal angle between local magnetic
and geographical meridians, expressed as E or W to indicate
direction of magnetic pole from true. Also called
declination (see grid*).
2 Detailed schedule of change orders or special
furnishings or equipment specific to one customer.
3 Small periodic change in astronomical latitude of
Earth locations due to wandering of poles.
varicam Pioneer variable-camber aerofoil.
varicowl Generalized term for any variable-geometry
inlet, esp. for main engine.
vario VSI (F, colloq.).
variocoupler RF transformer with fixed and moving
windings.
variometer 1 Aneroid-type VSI (traditional term of
gliding fraternity; * used to seek thermals).
2 Variable inductive coupler with fixed and moving
coils or rotors for comparing magnetic fields, esp. Earth’s
field.
varistor Two-electrode semiconductor resistor
characterized by resistance varying inversely with applied
V, in either direction of current.
Varite Resistor characterized by negative temperature
coefficient of resistance.
varnish 1 Solutions of resins, eg common gum or wood
rosin, in drying oil, eg linseed.
2 Thick slimes in overheated lubricant.
Varsol Naptha-like petroleum solvent (trade name).
Vartm, VARTM Vacuum-assisted resin transfer
moulding [molding].
Vartoms Variable rotor speed and torque-matching
system.
VAS 1 Visual augmentation system, or sleeve.
2 Voice-activated, or awareness, system.
3 Visible/IR spin-scan radiometer atmosphere sounder.
VASI, Vasi Visual approach slope indicator.
Vasis Vasi system (UK style).
Vast 1 Versatile avionics shop test(er); packaged
laboratory for installation on Navy airfields or carriers;
occasionally ‘a’ held to mean automatic.
2 Vibration analysis systems technique (GE).
3 Virtual air and space technology (NASA/FAA).
Vastac Vector-assisted attack.
Vastac
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