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terminal of an electrical source to its negative terminal. The actual movement within an electrical circuit is
that of electrons and is called electron current.
The arrowhead in a semiconductor diode symbol points in the direction of conventional current,
while electron current moves in the opposite direction.
conventional landing gear (airplane landing gear). The type of airplane landing gear with the main
wheels ahead of the center of gravity and a small wheel supporting the tail when the airplane is on the
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ground.
A conventional landing gear requires a great deal of pilot skill to keep the airplane from ground
looping (accidentally turning around) when it is moving at a fast speed on the ground.
The other type of landing gear, which is now the most commonly used, is the tricycle landing gear.
The two main wheels are behind the center of gravity, and the auxiliary wheel supports the aircraft nose.
converge. To draw closer together and eventually to meet. Converging lines are lines which, if continued,
will meet and cross one another.
convergence (meteorology). The condition that exists when the distribution of winds within a given area is
such that there is a net horizontal inflow of air into the area. In convergence at lower levels, the removal of
the resulting excess air is accomplished by upward movement.
Clouds and precipitation are likely to occur in areas of low-level convergent winds.
convergent-divergent duct. A duct that has a decreasing cross section in the direction of flow (convergent)
until a minimum area is reached.
After this point, the cross section increases, or becomes divergent. Convergent-divergent ducts are
called CD ducts, or in the United Kingdom, con-di ducts.
convergent-divergent exhaust duct (gas turbine engine exhaust duct). An exhaust duct used on the
engine of a supersonic aircraft. The cross-sectional area of the duct decreases in the direction of the gas
flow until it is small enough that the gases passing through this area travel at the speed of sound. Beyond
this point of minimum area, the duct enlarges so the gases can be further speeded up above the speed of
sound.
convergent-divergent inlet duct (supersonic airplane component). A form of duct, or passage, used for
the inlet air to supersonic airplane engines.
The forward section of the duct is convergent (it becomes smaller in the direction of the airflow).
The air entering the duct at a supersonic speed is slowed to a speed of Mach one by a shock wave in the
narrowest part of the duct.
Beyond this point, the area of the duct increases — becomes divergent. The air, now traveling
slower than the speed of sound, is further slowed, and its pressure increases.
convergent duct. A duct, or passage, whose cross-sectional area decreases in the direction of fluid flow.
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conversion coating (aircraft finishing system component). A chemical solution used to form an airtight
oxide or phosphate film on the surface of aluminum or magnesium parts. The conversion coating prevents
air reaching the metal and keeps it from corroding.
convertaplane (aircraft design). A type of heavier-than-air aircraft able to rise and descend vertically. The
convertaplane rises vertically by using rotors similar to those on a helicopter. But, when it is in the air, the
rotors can be tilted forward to produce thrust to pull the convertaplane through the air as a fixed-wing
aircraft.
converter (electrical machine). A rotating electrical machine that changes, or converts, alternating current
into direct current. A converter is usually a form of motor-generator, in which an AC motor drives a DC
generator.
convex surface. A surface that is curved outward with its outer edges lower than the center.
coolant. A fluid used to remove heat from a component or a system. A mixture of ethylene glycol and
water is normally used as a coolant in liquid-cooled aircraft engines.
cooling fins. Thin ribs that extend outward from a surface to carry heat from the surface into the air
flowing through the fins.
The cylinders of air-cooled aircraft engines are finned to increase their surface area, so a
maximum amount of heat can be transferred from the cylinder into the air.
coordinated universal time (UTC). Time corrected for the seasonal variations in the earth’s rotation about
the sun. Coordinated universal time is also known as universal time coordinated (thus UTC), Greenwich
mean time (GMT), and Zulu time.
coordinates (air traffic control). The intersection of lines of reference, usually expressed in
degrees/minutes/seconds of latitude and longitude, used to determine a position or location.
　
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