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35% distillates in the kerosine range. JP-4, the equivalent of commercial Jet-B fuel is a primary fuel for
military jet aircraft.
JP-8 (gas turbine engine fuel). A gas turbine engine fuel which is a form of highly refined kerosine. JP-8
is the NATO equivalent of Jet-A fuel.
jumper (electrical circuit). A short wire used to temporarily connect two points in an electrical circuit.
Jumpers are normally used to temporarily bypass a portion of a circuit for test purposes and for
troubleshooting.
jump seat. A removable seat that can be set up between, and slightly behind, the pilot’s and copilot’s seats
in an airplane. A flight mechanic (flight engineer) or observer riding in the jump seat can watch the
instruments and can operate some of the auxiliary controls.
junction (thermocouple). The point in a thermocouple at which the dissimilar metals join. A thermocouple
has two junctions: the hot, or measuring, junction, and the cold, or reference, junction.
junction box (electrical equipment). A box in which electrical wires can be joined and the junction of the
wires protected from damage. Junction boxes are normally made of metal or fiberglass-reinforced plastic.
junction field effect transistor. See JFET.
junction transistor. A semiconductor device made of three layers of doped silicon or germanium. In an
NPN junction transistor, layers of N-material are used as the emitter and collector. Between the two layers
of N material is a very thin layer of P-material, which acts as the base. Electrons flowing between the
emitter and base control the electrons flowing between the emitter and collector.
A PNP junction transistor is like an NPN transistor except that the base is made of N-material
between an emitter and collector of P-material. See illustration for bipolar transistor.
jury strut (airplane structure). A small strut that connects the center of the main wing struts of a
strut-braced monoplane to the wing spar. A jury strut stiffens the main struts to prevent their vibrating.
K
K. The abbreviation for the unit of measurement in the metric system equal to one thousand. K stands for
kilo. In computer use, K is a measure equal to the number two, raised to its tenth power (210), and this is
equal to 1,024. A computer with a memory of 64K has a memory that can actually store 65,536 bits of
information.
kaolin. A fine, white clay used for making ceramic materials and as a filler for certain types of plastic
resins.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 338
katabatic wind (meteorology). Any wind blowing downslope. Fall winds, foehns, chinooks, and Santa
Anas are katabatic winds.
K-band (aircraft radar). A type of radar that operates in the frequency range from approximately 10.9 to
36.0 gigahertz. The wavelength of K-band radar is between about 2.73 to 0.83 centimeters.
keel (seaplane structure). The main longitudinal structural member extending along the center line of the
bottom of a seaplane hull or float.
keeper (magnet). A piece of soft iron placed across the poles of a magnet when the magnet is not being
used. Magnetic energy is used to force lines of flux through the air between the poles, and the loss of this
energy partially demagnetizes the magnet.
The amount of energy used is determined by the reluctance (the opposition to the passage of the
lines of flux) of the material between the poles. The soft iron keeper has a very low reluctance compared
with air, and when the lines of flux travel through the keeper rather than through the air, less energy is used,
and the magnet self-demagnetizes less.
Kelvin bridge (resistance measuring instrument). A form of precision resistance-measuring instrument
which is a modification of the Wheatstone bridge. A Kelvin bridge minimizes the effect of lead and contact
resistance and is used for accurate measurements of low resistances.
Kelvin temperature (absolute temperature). Temperature measured from absolute zero on a scale using
the same divisions as are used in the Celsius system. Water freezes at 273°K and boils at 373°K.
Kennelly-Heaviside layer (atmospheric layer). A layer of ionized particles in the atmosphere at an
altitude of between 100 and 120 kilometers above the surface of the earth. Some radio waves cannot
penetrate these particles, and they bounce back to the earth. The Kennelly-Heaviside layer is also called the
Heaviside layer and the E-layer.
kerf. The slit (the narrow slot, or opening) made by a saw blade as it cuts through wood, metal, or plastic,
or by a cutting torch as it cuts through metal.
kerosine (petroleum product). A light (specific gravity of about 0.8), almost colorless hydrocarbon liquid
obtained from crude oil by the process of fractional distillation. Kerosine is used as a fuel for lamps and
　
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