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fuselage of a jet-propelled aircraft.
pyrometer. An instrument used to measure high temperatures. Pyrometers usually begin measuring at
temperatures above about 600°C.
Pythagorean theorem (mathematics). The statement that the square of the length of the hypotenuse of a
right triangle is equal to the square root of the sum of the squares of the lengths of the other two sides.
Q
Q-band radar. Radar that operates in the frequency band from 36 to 46 gigahertz. At this frequency, the
wavelength of the energy is between 0.834 and 0.652 centimeter.
QEC assembly (engine maintenance unit). An engine change assembly (quick engine change) that allows
an aircraft engine to be changed with the least amount of downtime. The engine is mounted on the engine
mounts, all of the accessories and the propeller are mounted on the engine, and the cowling is installed. The
QEC assembly essentially contains everything forward of the firewall.
Q-factor of a coil. A measure of the quality factor of the coil. Q is the ratio of the inductive reactance of a
coil to its resistance, both measured in ohms.
quadrant (aircraft controls). The housing in an aircraft cockpit on which the engine control levers are
mounted. The top of the quadrant is in the shape of a quarter of a circle, and the control levers stick out
radially from the quadrant.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 467
quadrant (air traffic control). A quarter part of a circle, centered on a navaid, oriented clockwise from
magnetic north as follows: NE quadrant 000°-089°, SE quadrant 090° – 179°, SW quadrant 180° – 269°,
and NW quadrant 270° – 359°.
quadrant (mathematics). One of the four parts of a plane formed by the system of rectangular coordinates.
The four quadrants are numbered with Roman numerals. I is the upper right-hand quadrant, II, the upper
left-hand. III is the lower left-hand, and IV, the lower right-hand quadrant.
quadrantal error. The error in an automatic direction finder system installation caused by the metal in the
aircraft. The quadrantal error is different in each of the four quadrants (front right, front left, rear left, rear
right).
quadratic equation (mathematics). An algebraic equation that contains both the first and second powers
of the unknown quantity, as well as a constant term. An example of a quadratic equation is:
ax2 + bx + c = 0
quadrilateral. A plane (flat), closed polygon with four sides. Squares, rectangles, parallelograms, and
trapezoids are all forms of quadrilaterals.
quadrivalent element (chemical element). A chemical element with four electrons in its valence shell.
Carbon, silicon, germanium, tin, and lead are quadrivalent elements.
quality control. A system of control in a manufacturing company that is responsible for the quality of the
product produced by the company. The inspection department is normally a part of the quality control
department.
quantum theory. The theory which states that an atom or molecule does not absorb energy in a continuous
and even fashion. Energy is absorbed in steps (quanta), with the amount of energy in each step being
related to the frequency of the energy.
quart. A unit of volume measurement. One quart is equal to: two pints; one-fourth U.S. gallon; 57.75 cubic
inches; 9.46 x 10-4 cubic meters.
quartersawed wood. Wood sawed from a tree in such a way that the annual rings cross the plank at an
angle of greater than 45°.
quarter-wave antenna. A radio antenna whose length is one quarter of the wavelength of the frequency
for which the antenna is used.
quartz. A mineral (silicon dioxide) found in nature as a hexagonal (six-sided) crystal. Quartz has
piezoelectric characteristics, as it produces a voltage when it is bent or pressed, and it changes its shape
when a voltage difference exists across two of its faces.
quartz crystal. A thin slab of quartz, used to control the frequency of an electronic oscillator. A quartz
crystal vibrates at its natural resonant frequency when it is excited with a pulse of electrical energy. As the
crystal vibrates, it produces an alternating current whose frequency is determined by the physical
dimensions of the crystal.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 468
quartz glass. A type of glass made from pure quartz. Quartz glass does not filter out ultraviolet rays.
quartz-iodine lamp. An incandescent lamp with a tungsten filament and a quartz envelope. The envelope
is filled with iodine vapor that reacts with the vaporized tungsten to prevent the tungsten vapors from
darkening the quartz envelope.
quartz lamp. A mercury-vapor lamp enclosed in a transparent housing made of quartz, rather than glass.
　
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