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the fastener.
wrinkle finish. A rough paint finish that is often applied to aircraft instrument panels. The surface of
wrinkle-finish paint dries quickly, and the material below the surface shrinks as it dries. The shrinkage
pulls the surface into a series of small wrinkles. A wrinkle finish does not show fingerprints or small
scratches as much as a smooth finish.
wrist pin (reciprocating engine component). The hardened and polished steel pin that attaches a piston to
the small end of a connecting rod. Wrist pins are called piston pins, and in the United Kingdom, gudgeon
pins.
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Page 633
wrought iron. A commercial grade of iron used for the manufacture of low-strength items. Wrought iron is
malleable (it can be shaped by hammering), tough, and relatively soft.
wye connection (electrical connection). A name that is often used for a Y- or star-connected electrical
circuit.
See Y-connection.
X
X-axis. The longitudinal, or roll axis of an aircraft. The vertical axis is the Z-axis, and the lateral axis is the
Y-axis. See longitudinal axis.
X-band radar. Radar whose energy is transmitted in a frequency band of between 5.2 and 10.9 gigahertz,
and whose wavelength is between about 5.77 and 2.75 centimeters.
xenon. An inert, colorless, odorless, gaseous chemical element. Xenon’s symbol is Xe, its atomic number
is 54, and its atomic weight is 131.30. Xenon is extracted from liquified air, and it is used to fill
stroboscopic lamps because it gives off a brilliant flash of light when it is ionized and current flows through
it.
X-ray inspection. A form of nondestructive inspection in which a piece of photographic film is exposed by
X-rays passing through a section of the aircraft structure. The density of the structure determines the
amount of energy passed to the film. Because of the different densities of the structure, an image of the
structure is formed on the film.
X-ray inspection is used to examine the inside of a structure for corrosion or damage that deforms
the structure.
X-rays. Rays of electromagnetic energy having a wavelength of approximately one angstrom. X-rays are
produced by accelerating electrons to a high velocity and then stopping them instantly by collision with a
solid object.
X-rays are able to penetrate many types of solid objects and are used to produce a photographic
record of the inside of an aircraft structure.
xylene. A flammable, oily, aromatic, hydrocarbon fluid. Xylene is mixed with other hydrocarbon fluids and
used as a solvent and as an additive to improve the combustion characteristics of reciprocating engine fuels.
Y
yagi antenna (radio antenna). A highly directional antenna used for high-frequency (HF) radio
communications. A yagi antenna has a single dipole connected to the transmission line (this is the driven
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 634
dipole) and several unconnected dipoles parallel to the driven dipole. These unconnected dipoles act as
reflectors and directors for the radio-frequency energy transmitted from the antenna.
yard (unit of measure). A unit of length in the English system of measurement. One yard is equal to 36
inches, three feet, or 0.9144 meter.
yardstick. A wooden measuring stick with the length of three feet, or one yard. A yardstick is marked at
every inch along its length.
yaw (aircraft flight condition). A flight condition of an aircraft in which the aircraft rotates about its
vertical axis. Yawing is not the same as turning, because an aircraft can be yawed and continue in straight
flight with the wind striking it from the side. When an airplane is turned, it follows a curved flight path,
with the wind always flowing parallel to its longitudinal axis.
yaw damper (airplane control). A part of an aircraft automatic flight control system used to keep the
aircraft from unwanted yawing. Yaw dampers are generally needed for swept-wing airplanes because of the
tendency of this type of airplane to Dutch roll. See Dutch roll.
Y-axis. The lateral, or pitch, axis of an aircraft. The vertical, or yaw, axis is the Z-axis, and the longitudinal,
or roll, axis is the X-axis. See lateral axis.
Y-connected circuit (electrical circuit). A three-phase alternating current circuit in which one end of each
of the three windings of a three-phase generator or transformer is connected to form a common point. In a
Y-connected circuit, two windings are in series with each other, and the current flowing in each of the two
windings is 120 electrical degrees out of phase with the current flowing in the other windings.
The voltage across the ends of the two windings is 1.73 times the voltage across either of the
　
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