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VORMB, VOR/MB
indicator or (esp. in light aircraft) simple VOR receiver
with localizer needle only.
VORMB, VOR/MB VOR marker beacon.
Vormet Sends scripted pilot’s weather reports to overflying
aircraft.
Vorpostenboot Flakship (G).
Vortac Combination of VOR and Tacan (occasionally
written VOR/TAC) offering from one fixed station VOR
az, Tacan az and Tacan (DME) distance information;
ident codes prove VOR and Tacan signals are both from
same fixed station. Normally * is end-product of trying to
integrate civil (VOR/DME) with military (Tacan)
navaids, latter being u.h.f. and therefore inherently
incompatible.
vortex Fluid in rotational motion (possessing vorticity),
eg streamed behind wingtip or across leading edge of
slender delta. See line *, point *, trailing *.
vortex breakdown Sudden separation of large vortex
from leading edge of slender delta (naturally followed by
its decay) at particular AOA (higher than stalling AOA
for most wings); essentially represents stall of slenderdelta
wing.
vortex burst See vortex breakdown.
vortex dissipator Bleed-air jet(s) blown down below and
ahead of jet-engine inlet to prevent ingestion of material
from unpaved airfields or contaminated runways.
vortex drag Drag caused by vortex formation; not
normally a recognized part of aircraft drag.
vortex filament Line along which intense (theoretically
infinite, at R = 0) vorticity is concentrated; either closed
loop or extending to infinity.
vortex flap Hinged along its leading edge just behind
leading edge of wing on upper surface. Opened to 45°
traps vortex to increase lift.
vortex flow Fluid flow combining rotation with translational
motion.
vortex generator Small flat blade perpendicular to skin
of aircraft or other body set at angle to airflow to cause
vortex which stirs boundary layer, usually to increase
relative speed of boundary layer and keep it attached to
surface; also called turbulator.
vortex hazard Danger to aircraft, esp. light aircraft,
from powerful vortices trailed behind wingtips of large
aircraft; also called wake hazard, wake turbulence.
vortex lift Lift generated by slender delta or similar wing
having sharp, acutely swept leading edge (subsonic
relative velocity normal to leading edge): large and
powerful vortex is shed evenly on left/right wings, adding
major non-linear increment to lift; also postpones stall to
lower speed and extreme AOA, but with high drag.
vortex line Line whose direction at every point coincides
with rotation vector, all of whose tangents are parallel
with local direction of vorticity. Must be closed curve or
extend to infinity, or to edge of fluid or to a point on an
infinitely intense vortex sheet.
vortex panel A hypothetical treatment of aerofoil circulation
by dividing the flow into a series of nodes on the
surface.
vortex ring Vortex forming closed ring (eg smoke ring);
collar vortex, and formed by helicopter as it slows to the
hover.
vortex-ring state Operating state of rotorcraft (esp. helicopter)
main rotor in which direction of flow through
rotor is in opposite sense to relative vertical flow outside
VP
rotor disc and opposite to rotor thrust. Occurs in autorotative
landing, and can occur with rotor under power if
rate of descent equals rotor downwash velocity.
vortex separation Filtration of different types of particle
from fluid by different centrifugal forces in vortex motion.
vortex sheet Theoretical infinitely thin layer of fluid
characterized by infinite vorticity; in practice layer of
finite thickness formed by large number of small vortices,
eg as trailed behind lifting wing (where much of vorticity
is quickly rolled up into two large tip vortices).
vortex street See street.
vortex strength Circulation round any body or other
closed system, symbol Γ, constant at all points on a vortex
filament.
vortex trail Visible (white) trail from wingtip, propeller
tip etc, caused by intense vortex.
vortex tube Device devoid of moving parts in which pressure
difference induces fluid flow through tangential slots
into tube; violent vortex divides flow into surrounding
warm flow and cold (about 40°C cooler) core.
vortex turbine Mounted in optimum location at wingtip
to extract power from tip vortex.
vorticity Vector measure of local rotation in fluid; in
uniformly rotating fluid proportional to angular velocity
(in UK, exactly defined as twice angular velocity). Symbol
q [some authorities use ] = V¯ V where V¯ is del (mathematical
operator) and V is vector velocity (° curl V in US;
often called rot. V, from rotation, in Europe).
vorticity component Circulation around elementary
surface normal to direction of vorticity divided by area of
surface; more strictly, limit of circulation as area of
element approaches zero.
vortillon Name coined by McDonnell Douglas to
describe fence around underside of DC-9 wing leading
edge controlling boundary-layer direction.
VORW VOR without voice.
VOS 1 Velocity of sound.
2 Voice-operated switch.
VOT, Vot VOR test signal; ground facility for testing
accuracy of VOR receivers.
voter Binary logic element or device which compares
signal condition in two or more channels and changes
state whenever a predetermined signal mismatch occurs,
usually to exclude a minority ‘outvoted’ signal. Also
called a * monitor.
voter threshold Difference between signals at which
voter is switched or triggered; normally difference
between one selected signal and mid-value signal from all
others in parallel system.
voting system System in which outputs of several
parallel channels are sensed and compared by voter so
that any single malfunctioning channel may be excluded.
Votol, VOTOL Vertical-only take-off and landing.
VOWS, Vows Valuation of weight saved; measure of
financial reward (usually in increased annual earning
power) from cutting each unit of mass (kg or lb) from
empty weight; eg VOWS for Concorde in 1974 currency
was £50/lb.
VOx Vanadium oxide.
VOX See Vox.
Vox Voice (communication, keying or activation).
VP 1 Variable-pitch.
2 Code: fixed-wing patrol squadron (USN); suffix B
adds bomber.
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