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the pinion.
rack-and-pinion actuator (fluid power actuator). A form of rotary actuator in which the fluid acts on a
piston on which a rack of gear teeth is cut. As the piston moves, it rotates a pinion gear which is mated with
the teeth cut in the rack.
radar. An electronic device which, by measuring the time interval between transmission and reception of
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radio pulses and correlating the angular orientation of the radiated antenna beam or beams in azimuth
and/or elevation, provides information on range, azimuth, and/or elevation of objects in the path of the
transmitted pulses. Radar, an acronym for RAdio Detecting And Ranging, was developed as a military
system during World War II.
A pulse of high-frequency electrical energy is transmitted from a highly directional antenna. The
pulse travels until it strikes an object, then bounces back and is received by the antenna. The return pulse
causes a bright spot to appear on the screen of a cathode-ray tube.
Radar is used for detecting precipitation, for navigation, and for detecting obstructions to flight.
Simplified radar is used for measuring the speed of vehicles on our highways.
radar altimeter. See radio altimeter.
radar altitude. The altitude of an aircraft determined by a radar-type radio altimeter. It is the actual
distance between the aircraft and the nearest terrain feature.
radar beacon transponder. A type of radar used to identify aircraft flying along controlled airways.
Ground radar at the airways traffic control center transmits a pulse of electromagnetic energy. When this
pulse is received by the transponder, it replies with a special coded pulse.
The coded reply is received by the ground radar and displayed on the controller’s radar scope to
show the location of the aircraft. An encoding altimeter directs the transponder to use a code that shows the
altitude the aircraft is flying. This altitude shows up as numbers beside the return on the radar screen.
radar beam. A beam of focused electromagnetic energy radiated by radar. It is similar to a flashlight or
searchlight beam, except that the frequency of the electromagnetic energy is beyond the visible range.
radar clutter (ICAO). The visual indication on a radar display of unwanted signals.
“Radar contact lost” (air traffic control). A phrase used by ATC to inform a pilot that radar data used to
determine the aircraft’s position is no longer being received or is no longer reliable, and radar service is no
longer being provided.
The loss may be attributed to several factors, including the aircraft merging with weather or
ground clutter, the aircraft operating below radar line of sight coverage, the aircraft entering an area of poor
radar return, failure of the aircraft transponder, or failure of the ground radar equipment.
radar identification (air traffic control). The procedure for ascertaining that an observed radar target is
the radar return from a particular aircraft.
radar mile. The time in microseconds needed for a pulse of radar energy to travel a distance of one
nautical mile and return to the radar receiver. One radar mile is approximately 12.4 microseconds.
radarsonde observation (radar meteorology). A weather observation in which winds are measured by
radar tracking a balloon-borne target.
radial (electronic navigation term). A line of radio bearing radiating outward from a very-high-frequency
omnirange (VOR) navigation facility. There are 360 radials radiating out from each VOR, and each radial
is named for the number of degrees clockwise from magnetic north that the radial leaves the facility.
radial bearing load. The load on a bearing that is perpendicular to the shaft on which the bearing is
mounted. Centrifugal loads are radial loads.
radial engine. A form of reciprocating engine that was at one time very popular for use on aircraft. The
cylinders are arranged radially around a small central crankcase. Radial engines have an exceptionally good
power-to-weight ratio, but they have so much frontal area that they cause an excessive amount of
aerodynamic drag and are not efficient for modern high-speed airplanes.
radial-inflow turbine. A type of turbine that uses a wheel similar to the wheel of a centrifugal air
compressor. The hot exhaust gases that drive the turbine flow in through its outer rim and out its center.
Radial-inflow turbines are used to drive the compressors in turbochargers for reciprocating engines.
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radial lead (electrical component). The lead of an electrical component, such as a resistor or capacitor,
that protrudes from the side of the component (it radiates outward). The other type of lead used on these
　
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