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used for cooling. Secondary air is not used in the combustion process.
secondary cell (batteries). A battery which can be recharged after it has been discharged. The action in
which chemical energy is changed into electrical energy is reversible. This means that electrical energy
from a battery charger can be changed into chemical energy to recharge the cell.
secondary color. A color produced by combining two primary colors in equal proportions. Green is a
secondary color made by mixing equal amounts of two primary colors, yellow and blue.
secondary controls of an airplane. Controls that modify the effect of the ailerons, rudder, and elevators of
an airplane, and do not in themselves cause rotation of the airplane about any of its three axes. Wing flaps,
trim tabs, servo tabs, spring tabs, and antiservo tabs are examples of secondary controls.
secondary current (electrical current). Current that flows in the secondary winding of a transformer.
Secondary current in a magneto ignition system is the high-voltage current induced in the secondary
winding of the magneto coil. It is this secondary current that flows through the distributor and produces the
spark at the spark plug.
secondary emission (electron tubes). Emission of electrons in an electron tube from an electrode other
than the cathode. Secondary emission takes place when electrons traveling at a high velocity strike the
anode (plate) and knock other electrons from it.
When secondary emission is a problem, a suppressor grid is installed near the anode. A negative
voltage on the suppressor grid suppresses the secondary emission by forcing the electrons that have been
knocked from the anode, back onto it.
secondary fuel (gas turbine engine fuel metering). The main flow of fuel from the fuel nozzles inside a
gas turbine engine. Primary, or pilot, fuel is used for starting the engine and for low-speed operation.
Secondary fuel allows the engine to produce its maximum power.
secondary radar. Radar which responds to pulses of energy transmitted from an interrogator. The response
is transmitted on a frequency different from that which was received.
secondary standard. A unit of length, weight, voltage, capacitance, time, or other value that is compared
with a primary standard to determine its accuracy. Secondary standards are working standards.
A clock, for example, is used as a secondary standard for measuring time, and it is calibrated by
comparing it to the time signal transmitted by radio station WWV. In this example, the signal transmitted
by station WWV is used as the primary standard.
secondary voltage. The voltage in an alternating current circuit produced across the secondary winding of
a transformer.
secondary winding (electrical transformer). The transformer winding connected to the electrical load.
The winding connected to the source of electrical energy is called the primary winding. If the secondary
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 508
winding has more turns than the primary winding, the transformer is a step-up transformer.
secondary winding (magneto coil). The winding in a magneto or ignition coil that connects to the
distributor rotor. The secondary winding is normally made of very small-diameter wire and has a large
number of turns, typically about 20,000.
second-class lever. A lever in which the fulcrum is at one end, and the lifting force is at the other. The
weight force is between the lifting force and the fulcrum. A wheelbarrow is an example of a second-class
lever.
second in command. 14 CFR Part 1: “A pilot who is designated to be second in command of an aircraft
during flight time.”
sectional chart. An aeronautical chart drawn to a scale of 1:500,000 (one inch is equal to eight statute
miles). Sectional charts are designed for visual navigation of slow- or medium-speed aircraft. Topographic
information on these charts feature the portrayal of relief and a judicious selection of visual checkpoints for
VFR flight. Aeronautical information includes visual and radio aids to navigation, airports, controlled
airspace, restricted areas, obstructions, and related data.
sectional view (aircraft drawing). A detail view in an aircraft drawing that shows the inside of a part. A
view of the main drawing is cut with a cutting plane, and the sectional view is drawn to show the shape and
construction of the piece along this cutting plane.
sectioning (aircraft drawing). The use of cross-hatching to indicate the type of material used in a sectional
view of a part on an aircraft drawing.
sector (part of a circle). A part of a circle bounded by two radii and the arc that lies between them.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
　
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