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vapour
vapour Substance in gaseous state but below critical
temperature; thus can be converted by pressure alone to
liquid or solid (US = vapor).
vapour blasting Surface treatment of [usually metal] part
by firing abrasive particles in high-velocity jet.
vapour cycle Closed-circuit refrigeration, eg for airconditioning,
in which heat is extracted by refrigerant
alternately evaporated and condensed.
vapour degreasing Immersion in hot solvent vapour, eg
trichlorethylene.
vapour gutter Assembly of rings and radial struts,
usually of > section, to retain flame in afterburner; also
called flameholder or stabilizer.
vapour lock Complete breakdown of supply of liquid, eg
fuel from tank, because of blockage by bubble of vapour
at high point in pipe.
vapour-phase inhibitor Nitrite-based chemical, often
locked in paper or other solid, which protects metal parts
against corrosion by preventing formation of vapour, esp.
of water; usually white powder which volatilises and
recrystallises on metal surface.
vapour pressure Pressure exerted by molecules of vapour
on walls of container; with mixture, sum of partial
pressures. Compared with kerosene, wide-cut fuels have
high volatility and thus high *, hastening boiling and
vapour lock.
vapour tension Maximum attainable vapour pressure
exerted by plane liquid surface with vapour above, varies
with temperature.
vapour trail See condensation trail.
vapour-type thermometer Needle is driven by Bourdon
tube sensing pressure from vapour capsule whose temperature
is that indicated.
V APP Approach speed.
VAPS, Vaps 1 Virtual avionics [or applications] prototyping
system.
2 Visual approaches.
Vaptar Variable-parameter terrain-avoidance radar.
VAQ Unit prefix: airborne early-warning squadron
(USN).
VAR 1 V.h.f. aural range, ie radio range.
2 Visual/aural range; radio range in which two airways
are located by A/N signals and two by visual means, eg
panel instrument (obs.).
3 Volt/ampere(s) reactive; unit of wattless (reactive)
electrical power.
4 Vacuum-arc remelting.
5 Variation.
6 Volcanic-activity reporting.
var Variation (magnetic).
varactor Device employing p-n junction whose
capacitance is varied by reverse voltage; important in
parametric amplifiers.
VARI Vacuum-assisted resin injection.
variable When applied to IGV or stator ring, means
variable-incidence; when applied to jet-engine inlet or
nozzle, means variable profile and area.
variable-area nozzle Propelling nozzle whose crosssection
area can be altered (usually, together with profile)
to match changed Mach number and afterburner
operation (airbreather) or atmospheric pressure from SL
to vacuum (rocket).
variable-geometry engine
variable-area vane box Mounted directly under fixedaxis
quasi-vertical lift jets [e.g., LiftFan], vectors thrust
over large angle about transverse axis.
variable-area wing Rare arrangements have included
variable span and even retractable lower wing of biplane
into upper, but modern flap systems (eg Fowler) give
significant change.
variable camber 1 Apart from experimental aircraft,
most important methods are hinged leading and trailing
edges, eg F-16, which can each be pivoted slightly up,
centred or pivoted fully down independently to suit
desired flight condition. Tail surfaces, eg tailplane,
rudder, are today often divided spanwise to change not
just surface angle but also camber, for greater power.
2 Camber is varied by elastic deformation of surface,
eg 747 Kruegers.
variable-camber flap 1 See anti-balance tab.
2 Flap, usually Krueger, whose profile changes on
extension.
variable colour stripping Removal of part[s] of spectrum
to indicate presence of organic material or explosive
devices.
variable-cycle engine Jet engine in which path of
working fluid can be altered by shutters/valves/doors, eg
to convert from turbojet or turbofan to ramjet, hybrid
rocket or other form in cruising flight. Some authorities
claim adding an afterburner and variable nozzle results in
a *.
variable-datum boost control Auto boost control for
supercharged piston engine in which governed boost
pressure increases as pilot’s throttle lever is opened.
variable-delivery pump Fluid pump whose output can be
varied independently of drive speed, usually by variableangle
swashplate driving stroked plungers (at 90° stroke
is zero).
variable-density tunnel Wind tunnel whose pressure can
be varied over wide range (usually not below atmospheric)
while in operation; normally pressurized to achieve
desired Reynolds number.
variable-diameter tilt-rotor Full diameter for takeoff,
transition to reduced diameter for fast translational flight.
variable-discharge turbine Gas turbine, eg driven by
piston-engine exhaust, whose throughput (mass flow) can
be controlled by valve (often called waste gate) to match
turbine power to altitude and other variables.
variable-displacement pump Fluid pump whose output
(mass flow) can be varied over wide range, often to zero,
for any given input drive speed; often synonymous with
variable-delivery, but ** explicitly implies reciprocating
plungers or pistons whose stroke is variable.
variable-floor-level bridge Passenger bridge whose
airside end can be raised and lowered to match aircraft sill
height.
variable-flow ducted rocket Propulsion for long-range
AAM and ASMs offering sustained supersonic [even
hypersonic] speed from combining rocket with ramjet.
variable-geometry aircraft Aircraft whose shape can be
varied in gross manner, ie more fundamentally than by
retractable landing gear or flaps; term has come to mean
variable wing sweep, so should not now be used in any
other context, unless circumstances change or clear
explanation of meaning is furnished.
variable-geometry engine Invariably refers to airbreathing
engine for supersonic propulsion in which for
746