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Y
Y 1 Yaw, yaw angle.
2 Lateral axis (strictly OY) or any measure or component
along that axis, esp. lateral force [e.g.,
helicopter-rotor side force], or cross-stream distance in
wind tunnel.
3 Admittance.
4 IATA symbol, tourist class.
5 US DoD aircraft designation prefix; prototype/
service-test quantity.
6 Yttrium.
7 Year (eg in FY, fiscal *).
8 Adiabatic factor.
9 Bessel function of the second kind.
10 Induced pressure, eg caused by presence of jet.
11 Rules governing change from IFR to visual.
12 Prefix yotta, multiplied by × 10 24 .
13 Other meanings include yes (affirmative) and yellow.
y 1 Vertical axis (ordinate) of cartesian coordinates or
graphical figure.
2 Any value measured parallel to (1) or any co-ordinate
point measured along that axis.
3 Admittance (Y is more common).
4 Perpendicular distance from extreme [surface] fibre to
neutral axis.
5 Prefix yocto, = × 10 -24 .
6 Maximum transverse deflection of a beam.
7 Today often used instead of Y(2).
ȳ 1 Co-ordinate position of c.g. along OY axis (normally
at or near origin).
2 Sample average value.
3 Spanwise c.p. position expressed as f (b/2).
Ȳ - Spanwise location [distance from aircraft centreline] of
centroid of wing area.
Y ,y Lateral aixis fixed relative to direction of flight.
Y ,y Lateral axis relative to Earth or space.
Y-allocation Second group of 126 frequency-paired
Tacan/civil DME channels.
Y-alloys British aluminium alloys originally developed by
Rolls-Royce and HDA for pistons, typically with 4% Cu,
2% Ni, 1.5% Mg and other elements, which because of their
retention of strength to 250–300°C were chosen as ruling
materials for Concorde with names RR.58 (UK) and
AU2GN (F).
Y-axis See Y (2), y (1)
Y-channel See Y-allocation.
Y-connection One end of all three coils of 3-phase
electrical machine connected to common point while other
ends constitute 3-phase line; alternative to delta, also called
star.
Y-cut crystal Cut parallel to Z-axis, perpendicular to
Y-axis; thus parallel to one face of hexagaon.
Y-duct Leads from two [usually lateral] inlets to single
engine.
Y-loader Trolley with manually pumped hydraulic jack
for loading bombs and other stores, picking them up from
stillage.
Y-plates Horizontally parallel deflector plates whose
potential difference positions electron beam vertically in
CRT.
Y-scale Scale along line of principal vertical in oblique
reconnaissance imagery, or along any other line which on
ground area shown would be parallel to this.
Y-section Structural section resembling Y, often with
flanged or beaded edges.
Y-service Electronic intelligence (UK, WW2).
Y-valve Lube-oil drain valve from dry sump.
Y-winding See Y-connection.
YAF Yesterday’s Air Force, California (US).
YAG, Yag Yttrium aluminium garnet Y 3 Al 5 O 12 .
Yagi aerial Directional aerial comprising driven dipole,
reflector and one or more (usually linear array) parasitic
dipole directors spaced at 0.15–0.25 wavelength; maximum
radiation is projected parallel to long axis.
yard Traditional Imperial unit of length = 0.9144 m
exactly.
yaw Rotation of aircraft about vertical (OZ) axis; positive
= clockwise seen from above; symbol ψ.
yaw damper Automatic subsystem in aeroplane (usually
jet) FCS which senses onset of yaw and immediately applies
corrective rudder to eliminate it. Early types were called
parallel because they operated whole circuit including
pedals; modern series ** has no effect on FCS further
forward than fin (though sensing gyro may be near c.g.) and
its activity is unnoticed by pilot. Most aircraft are flyable
throughout virtually whole flight envelope with ** inoperative.
yawed wing Wing proceeding obliquely to relative wind;
slewed wing.
yaw guy Cable along ground under mooring airship for
attachment of yaw-guy wires.
yaw-guy wires Ropes or cables dropped from bow of
airship before mooring for securing to yaw guys; these stop
nose from swinging.
yawhead Yaw sensor, eg angled pitots, on pivoted vane.
yawing moment Moment tending to rotate aircraft about
vertical OZ axis, symbol usually N = qSc¯c n where q is
constant, S is wing area, c¯ is mean chord and c n ** coefficient;
measured positive if clockwise seen from above.
yaw lines Yaw-guy wires (US).
yawmeter Instrument or sensor for detecting yaw; can be
simple device, eg yaw string or two or more pitot tubes at
different inclinations whose pressure difference is sensed, or
electronic gyro-fed subsystem.
yaw pointing Additional flight-control mode for some
modern fighters in which yaw can be controlled without
changing flight trajectory by varying sideslip angle while
holding zero lateral acceleration. Usually achieved by
deflecting vertical canard while linked to rudder(s) and rollcontrol
surfaces. Gives much quicker and better
gun-aiming.
yaw stability Tendency to reduce yaw to zero, also called
weathercock stability. The derivative can be written C n β.
yaw string Crude yawmeter comprising string, wool or
other filament allowed to align with relative wind, eg ahead
of windscreen.
yaw vane Small vertical aerofoil on long pivoted arm
giving weathercock indication of yaw.
Yb Ytterbium.
787