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direction the fluid is flowing, and when fluid flows through a converging nozzle at a subsonic speed, it
speeds up. The area of a diverging nozzle increases in the direction the fluid is flowing, and when fluid
flows through a diverging nozzle at a subsonic speed, it slows down.
nozzle diaphragm (gas turbine engine component). The ring of stationary vanes directly ahead of the
turbine wheel. The vanes in the nozzle diaphragm form a series of convergent ducts which accelerate the
air as it leaves the combustors and direct it into the turbine blades at the angle that gives the turbine its
maximum efficiency.
The nozzle diaphragm is also called the turbine inlet guide vanes. See turbine inlet guide vanes.
nozzle guide vanes. See turbine inlet guide vanes.
NPN transistor. A bipolar transistor made of three pieces of semiconductor material (silicon or germanium)
joined together. The emitter and collector are made of N-type material, and the base, which is sandwiched
between them, is made of P-type material.
N-struts (airplane wing struts). Interplane struts installed between the upper and lower wings of a biplane
near the wing tips. N-struts get their name from the fact that the three pieces of these struts are arranged in
the shape of the letter N.
NTAP (Notice to Airmen Publication). A publication issued every 14 days, designed primarily for the
pilot, which contains current NOTAM information considered essential to the safety of flight as well as
supplemental data to other aeronautical publications. The contraction NTAP is used in NOTAM text.
N-type semiconductor material. A semiconductor element, such as silicon or germanium, doped with an
element having more electrons in its valence shell than are needed to complete the covalent bonds within
the material. There are electrons in N-type material that are free to move about. Silicon and germanium are
doped with a pentavalent element, such as arsenic or phosphorus, to make N-type material.
NTZ (no transgression zone). A 2,000-foot-wide zone, located equidistant between parallel runway final
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 408
approach courses in which flight is not allowed.
nuclear energy. Energy released when neutrons are knocked out of the nuclei of certain materials.
Neutrons bind the protons together in the nucleus of an atom, and when neutrons are knocked out, the
protons are then able to leave the nucleus. As they leave, they release great amounts of energy in the form
of heat and light.
nuclear fission. The breaking apart of the nucleus of an atom by striking the nucleus with a neutron. If a
neutron strikes the nucleus with enough force, it splits the nucleus and creates atoms of different materials.
Nuclear fission releases a tremendous amount of heat and light.
nuclear fusion. A method of energy release in which a heavier nucleus is formed by fusing two lighter
nuclei. When the lighter nuclei fuse, a large amount of energy is released.
nuclei. A plural form of nucleus; an alternate plural form is nucleuses.
nucleonics. The branch of science and technology that deals with nuclear energy and its applications.
nucleus of an atom. The core (center portion) of an atom. The nucleus contains one or more protons
(positive charges), and all nuclei except that of hydrogen contain one or more neutrons. Neutrons have
mass but no electrical charge.
null balance. A method of setting one voltage exactly equal to another. When no current flows between the
two voltages, as indicated by a sensitive current-measuring instrument, the two voltages are exactly the
same. The voltages have nulled out, or cancelled, each other.
null detector (electrical instrument). An instrument used to measure a value by comparing it with a
known variable value. The known value is compared with the unknown and is changed until the null
detector determines that there is no difference between the two. The known value is now exactly the same
as that of the unknown.
null position (automatic direction finder). The position of an ADF loop antenna when the signal being
received is canceled in the two sides of the loop, and the signal strength is the weakest.
numbers. Terms used to assign a value or an order to something. Cardinal numbers, such as 1, 2, and 3, tell
how many. They assign a value to something. One engine, 2 wrenches, 3 airplanes are examples of cardinal
numbers being used to assign values.
Ordinal numbers, such as first, second, and third, tell us the order in which something occurs. The
first day, the second order, or the third time are examples of the use of ordinal numbers.
numerator (mathematics). The part of a common fraction above the line; the denominator is the part of
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航空术语词典Dictionary of Aeronautical Terms 中(149)
