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weathervane stability
and for weathercocking tendency of aircraft on ground to
face into wind. Hence * effect of vertical tail, which
progressively gives directional stability to VTOL aircraft
as forward speed increases.
weathervane stability That provided in flight by fixed tail
surfaces.
weave 1 To make continuous and smooth changes of
direction and height while over a period following a
desired track; weaving assigned to proportion of fighters
escorting slower aircraft so that continuous watch could
be kept astern and in other difficult areas. Hence, weaver.
2 Angular wander of spin axis, esp. of gyro, radar
scanner, rotary mirror etc.
WEB Web effective burn (time).
web 1 Principal vertical member of a beam, spar or other
primary structure running length of wing or fuselage,
providing strength necessary to resist shear and keep
upper and lower booms (chords) correct distance apart.
Occasionally expanded to * member, * plate.
2 In solid-propellant rocket, distance through which
propellant burning surface will advance from initial
surface until * burnout as defined by two-tanget method;
usually measured as linear distance perpendicular to
initial surface, symbol τ w .
3 Any material form resembling sheet, either as discrete
pieces or continuous * unrolled from drum or coil; esp.
sheet form of prepreg, supplied in standard widths.
web average burning-surface area Total volume of solid
rocket propellant, excluding slivers, divided by web; thus
has dimensions of an area, symbol A s .
webbing Strong close-woven fabric strip produced to
specified UTS, used eg for securing loose (bulk) cargo.
weber, Wb SI unit of magnetic flux; that flux which,
linking circuit of one turn, produces EMF of 1 V as it is
reduced to zero uniformly in 1 s. Symbol Φ. To convert
from maxwell, multiply by 10 –8 .
web fraction Web (2) divided by internal radius of motor
case or chamber; symbol f, expressed as %.
web rib Rib fabricated from sheet or plate.
WEC World Energy Conference.
WECMC Wing electronic-combat management, or
managers’, course.
WECPNL Weighted equivalent continuous perceived
noise level (see noise).
WED Water equivalent depth.
wedge 1 Air mass having wedge shape in plan, esp. such
a mass of high pressure extending between two lows.
2 Sharp-edged essentially 2-D * forming one wall of
2-D inlet of supersonic airbreathing engine, extending
ahead of inlet so that its shock may be focused on inlet lip
and normally extending rearwards as a variable ramp.
Hence * inlet.
3 Small * added above trailing edge of aileron [rarely,
other control surface] giving blunt trailing edge; supersonic
equivalent of aileron cord.
wedge aerofoil Sharp LE and blunt TE, useless except at
supersonic speed where efficiency is high, so confined to
use on missiles. See parallel double-*.
WEDS Weapons effects display system.
weeds, in the 1 At lowest possible level, on TFR or
manually (colloq.).
2 Location of [usually inadvertent] landing outside
airfield boundary.
weight
wee-heat A simple form of on/off turbojet afterburning.
weeping wing Fitted with liquid-injection leading-edge
de-icing.
wef, WEF With effect from.
Wefax Weather facsimile format; one selectable mode
of data transmission between weather satellite and ground
printout.
Weft Wings/engine(s)/fuselage/tail; most basic of
mnemonics used in early aircraft-recognition instruction.
WEG Weapons Evaluation Group (USAF).
Wehnelt Type of cathode whose emissivity is enhanced
by coating of radioactive-metal oxides.
Weibull analysis Standardised form of plotting component
failure against age, categorised as infantile, wear-out
and random.
Weick Coefficient for calculating propeller characteristic,
also called speed/power coefficient,
C s = V 5 ρ/PN 2 , where V is velocity of advance, ρ is
density, P is power and N is rpm See power/speed coefficient.
weighing Today almost all determination of aircraft
weight is done by moving landing gears over platforms
supported on load cells which measure forces by straingauges,
whose output may be summed and displayed
automatically. A few aircraft have landing-gear
hydraulics giving a cockpit readout of weight and c.g.
position.
weighing points Locations, published in engineering
documents and stencilled on aircraft, where jacks may be
applied in weighing process.
weighing record Hard copy updated each time aircraft is
weighed; includes c.g. position.
weigh-off Free ballooning of airship before casting off to
refine trim.
weight Force exerted on a mass by Earth’s gravity; thus
a figure unique to a particular location which by international
agreement is any at which g (free-fall acceleration)
is 9.80665 m/s. For modern aeroplane some measures
include: empty, complete aircraft plus systems measured
in accord with specification (eg in US military usage,
MIL-STD-3374); CCDR, empty minus items listed in
STD-25140A such as engine(s), starter(s), electrics and
avionics where removable direct from racking,
wheels/brakes/tyres/tubes; standard empty, bare aircraft
plus unusable fuel, full oil and full operating fluids (thus
excluding potable water); basic empty, standard empty
plus optional equipment; structure, bare airframe without
systems and equipment other than wing/tail movables and
flight-control power units, flap actuation, landing gear
and actuation, and equipped engine installation(s) minus
engines; useful load, those items that when added to *
empty (for transport, OEW) will add up to gross weight
for design mission (transport, MTOW); operating weight
(military), empty plus useful load minus expendable fuel
(internal/external), ammunition and stores; operating
empty (OEW), equipped empty + all consumables (fuel,
lube, filled galleys and bonded stocks, toiletries etc) +
removable furnishings, reading and entertainment
materials, cutlery, flight and cabin crews and their
baggage, ship’s papers; zero-fuel (ZFW), (military) operating
plus ammunition/missiles/stores, (transport)
MTOW minus usable fuel; gross (military), MTOW
(civil), allowable at moment of takeoff; ramp (MRW),
(civil) allowable at moment of starting engines; basic
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