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robot. A form of automated machine, used to replace a human operator in some tasks that are dangerous or
highly repetitive. Robots can be programmed to sense certain conditions and act in the correct way for the
conditions that exist.
robotics. The branch of science or technology that deals with the design, application, construction, and
maintenance of robots.
rocker arm (reciprocating engine component). A pivoted arm on the cylinder head of a reciprocating
engine. The pushrod forces one end of the rocker arm up, and as the other end moves down, it forces the
intake or exhaust valve off its seat.
rocker box. The enclosed part of a reciprocating engine cylinder head that houses the valve mechanism.
rocket. A flight vehicle propelled by expanding gases produced when the fuel combines with oxygen
carried in the vehicle. Rocket engines can use either liquid or solid fuel, and they are not dependent upon
oxygen in the atmosphere. Rockets are used to launch orbiting satellites.
14 CFR Part 1: “An aircraft propelled by ejected expanding gases generated in the engine from
self-contained propellants and not dependent on the intake of outside substances. It includes any part which
becomes separated during the operation.”
rocket engine. A form of reaction engine whose fuel and oxidizer contain all of the oxygen needed for the
release of heat energy. The released heat expands the gases which are ejected at a high velocity from a
nozzle at the rear of the rocket. Rocket engines can operate in outer space where there is no atmosphere.
rocketsonde (meteorology). A type of radiosonde launched by a rocket which makes its measurements
during a parachute descent. Rocketsondes are capable of obtaining soundings to a much greater height than
is possible by balloon or aircraft.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 496
rocking shaft (aircraft instrument component). A shaft used in the mechanism of a pressure-measuring
instrument to change the direction of movement by 90° and to amplify the amount of movement.
Rockwell hardness tester. A precision testing machine, used to measure the hardness of a material. A
diamond pyramid or hardened steel ball is pressed by an accurately calibrated force into the surface of the
material being tested. The depth to which the pyramid or ball penetrates the surface is measured with a dial
indicator. The greater the depth of penetration, the softer the material.
rock wool. A form of insulating material made by blowing a high-velocity stream of air through molten
rock. Rock wool is fireproof, and the dead air space it contains makes it a good thermal insulator.
roentgenology. The branch of science dealing with the use of X-rays.
roll (aircraft flight maneuver). Rotation of an aircraft about its longitudinal axis.
roll cloud (meteorology). A dense and horizontal roll-shaped cloud located on the lower leading edge of a
cumulonimbus, or less often on a rapidly developing cumulus. Roll clouds indicate the presence of
turbulence.
roller bearing. A form of antifriction bearing that supports the load on hardened steel cylinders rolling
between two hardened and polished races. Roller bearings are used for radial loads, rather than thrust loads.
roll pin. A press-fit pin used as a pivot in certain types of machinery. A roll pin is made of spring steel
sheet rolled into a small, open-sided cylinder. When a roll pin is pressed into a hole slightly smaller than its
outside diameter, it squeezes together to fit into the hole. The spring action trying to expand the pin to its
normal diameter holds it tightly in the hole.
roll threading. A method of forming threads on a bolt or rod by rolling the material to be threaded between
grooved rollers. No material is removed when the threads are rolled, as it is when they are cut.
root (mathematics). A number which, when multiplied by itself a specified number of times, will produce
a given number.
root (propeller blade nomenclature). The portion of a propeller blade that secures the blade in the hub.
root mean square (rms) (alternating current value). A value used to measure the heating effect of
sine-wave alternating current. The rms value is found by dividing one alternation of the AC into an infinite
number of instantaneous values. Each instantaneous value is squared (multiplied by itself), and all of the
squares are averaged to find the average, or mean, square. The square root is taken of this mean square.
The rms value of sine wave alternating current is 0.707 time the peak value of one alternation. One
ampere rms has a peak value of 1.414 ( ) amps and produces the same amount of heat as one amp of
direct current. The rms value is also called the effective value.
　
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