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layer of clouds or obscuring phenomena reported as ‘broken,’ ‘overcast,’ or ‘obscuration,’ and not
classified as ‘thin’ or ‘partial.’”
ceiling balloon (meteorology). A small, black, helium-filled balloon used to find the height of a base of
clouds.
The balloon is released by a weather observer, and the time needed for it to disappear into the
clouds is measured. Since both the rate of rise of the balloon and the time it took to disappear into the
clouds are known, the height of the base of the clouds can be determined.
ceiling light (meteorology). A light used by weather observers to measure the height of the bottom of a
layer of clouds at night. A beam of light, shone vertically upward, makes a spot of light on the bottom of
the cloud.
A theodolite (an instrument used to measure angles), located a known distance away from the light,
is used to measure the angle up to the spot of light on the cloud base.
By knowing the distance between the theodolite and the ceiling light and the angle measured by
the theodolite, the height of the cloud base can be determined.
ceilometer (meteorology). A cloud-height measuring system. A ceilometer projects a beam of light on the
cloud base, detects the reflection by a photoelectric cell, and determines the cloud-base height by
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 112
triangulation.
celestial navigation. A form of navigation used by airplanes and ships. Location fixes are found by
observing the angle between the observer and one of the navigational stars, and noting the exact time the
observation is made. The exact location of the navigational star at the time of the observation is found by
referring to a nautical almanac.
The location on the earth’s surface of the star at the time of observation and the angle between the
star and the observer are plotted on a navigational chart. Celestial navigation has been almost entirely
replaced by various forms of electronic navigation, which are more accurate and easier to use.
cell (electrochemical). An electrochemical device consisting of two electrodes surrounded by an
electrolyte. A potential difference exists between the electrodes that causes electrons to flow.
Celluloid. The registered trade name for one of the early thermoplastic materials. Celluloid is made from
cellulose nitrate and camphor.
cellulose. A material obtained from natural fibrous plants such as cotton and kapok. Cellulose is treated
with certain acids to make the base for some plastic materials.
cellulose acetate butyrate dope (aircraft finishing material). A form of finishing material for
fabric-covered aircraft made of a cellulose fiber dissolved in a mixture of acetic and butyric acids.
Plasticizers, solvents, and thinners are mixed with the film base to give it the proper working
qualities.
Cellulose acetate butyrate dope, also called CAB dope or, more simply, butyrate dope, has become
more popular than the older cellulose nitrate dope because it is far less flammable than nitrate dope.
cellulose nitrate. A compound made by treating cellulose with a mixture of nitric and sulfuric acids.
Cellulose nitrate is used as the base for certain plastics, and as a component in the manufacture of
explosives. Cellulose nitrate is also known as nitrocellulose and guncotton.
cellulose nitrate dope (aircraft finishing material). A form of finishing material for fabric-covered
aircraft made of a cellulose fiber dissolved in nitric and sulfuric acids. Plasticizers, solvents, and thinners
are mixed with the film base to give it the proper working qualities.
Cellulose nitrate dope (generally called nitrate dope) is an excellent adhesive, but it is being
replaced to a great extent by butyrate dope. Butyrate dope is not as good an adhesive, but it is much less
flammable.
Celsius temperature. Temperature measured on a scale that sets the freezing point of water at 0° and its
boiling point at 100°. There are 100 equal graduations called degrees between these two points. Absolute
zero is –273°C. Celsius temperature was formerly called centigrade temperature.
CEMF (counterelectromotive force). A voltage produced in the armature of an electric motor as the
armature windings cut across the fixed magnetic field. The polarity of the CEMF is opposite the polarity of
the voltage applied to the motor, and it opposes the applied voltage.
center. A point within an object that is the same distance from all points on the surface of the object.
center drill. A cutting tool which combines a twist drill and a 60° countersink. A center drill is used to drill
the center hole in a piece of metal so it can be mounted between the centers in a lathe.
　
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