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enough that the insulated thermocouple remains at the same temperature as the measuring thermocouples,
no signal is sent to the fire warning system. But if a fire occurs and the measuring thermocouple gets hot
before the insulated reference thermocouple, a voltage is produced that causes a current to flow and actuate
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 477
the fire warning system.
rate of yaw. The rate, usually expressed in degrees per second, at which an aircraft rotates about its vertical
axis.
rating. 14 CFR Part 1: “A statement that, as a part of a certificate, sets forth special conditions, privileges,
or limitations.”
ratio. A relationship between two quantities. A ratio of two to one (2:1) is a relationship in which the first
quantity is two times as large as the second.
ratiometer indicator mechanism. A direct current indicating instrument in which the pointer deflection is
proportional to the ratio between the current flowing in a reference coil and that flowing in the measuring
coil.
RATO (rocket assisted takeoff). RATO is a method of assisted takeoff that can be used by a heavily
loaded airplane when taking off from a high-altitude airport. Auxiliary boost rockets, attached to the
airframe, are ignited at the critical time during takeoff to provide the needed additional thrust.
rattail file. A long, narrow, tapered, round file. Rattail files are used for filing a radius in the corner of a
cutout.
rawhide mallet. A soft-face mallet whose head is made of a tightly wound roll of rawhide. Rawhide
mallets are used to form soft sheet metal and to pound parts that must not be damaged by hitting them with
a hard hammer.
rawinsonde observation (radar meteorology). A combined winds aloft and radiosonde observation.
Winds are determined by tracking the radiosonde by radio direction finder or radar.
RC circuit (electrical circuit). An electrical circuit that contains both resistance and capacitance.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 478
RC time constant. See capacitive time constant.
RDF (radio direction finding). A method of locating a radio transmitter by using radio receivers equipped
with directional antennas. The station to be located is received by two or more RDF stations, and the
bearings (the direction from the receivers to the transmitter) are plotted on a chart. The transmitting antenna
is located at the point the bearings from all of the RDF stations cross.
reach (spark plug design feature). The length of the threads on a spark plug shell. The reach needed by a
spark plug is determined by the thickness of the cylinder head into which the spark plug screws. The end of
the spark plug should be flush with the inside of the cylinder head.
A long-reach 18-mm aircraft spark plug has a reach of 13/16-inch; a short-reach 18-mm spark
plug has a reach of 1/2-inch.
reactance (X). Opposition to the flow of alternating current caused by capacitance and inductance in the
circuit. Reactance opposes the flow of alternating current without using any power.
Reactance caused by capacitance is called capacitive reactance, its symbol is XC, and it is
measured in ohms. Capacitive reactance causes the current in the circuit to lead the voltage.
Reactance caused by inductance is called inductive reactance, and its symbol is XL. Inductive
reactance is also measured in ohms, and it causes the current in a circuit to lag behind the voltage.
reaction. A response to an action that occurs in a direction opposite to the action. The recoil produced
when a gun is fired is an example of reaction. When the powder in the cartridge burns, the resulting gas
forces the bullet out the barrel. The action forcing the bullet from the barrel causes an opposing reaction
that pushes back on the gun with exactly the same amount of force.
reaction engine. A form of heat engine that produces thrust by heating a mass of air inside the engine and
discharging it at a high velocity through a specially shaped nozzle. The amount of thrust is determined by
the mass of the air and by the amount it is accelerated. Reaction engines which include rocket engines are
commonly called jet engines.
reaction turbine. A type of turbine wheel turned by an aerodynamic force produced by the turbine blades.
This force is similar to the lift produced by an aircraft wing. The blades of a reaction turbine are small
airfoils mounted on the periphery of the turbine wheel in such a way that they form converging ducts that
accelerate the hot gases passing through them. The high-velocity gas flowing over the reaction turbine
blades produces a pressure difference between the top and bottom of the blade. This pressure difference
　
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