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Roots-type air compressor. A positive-displacement air pump that uses two intermeshing figure-8-shaped
rotors to move the air.
rosette weld. A method of securing one steel structural tube inside another. Small holes are drilled in the
outer tube, and the inner tube is welded to it around the circumference of the holes. Rosette welds are used
to prevent the inner tube moving inside the outer tube. This type of weld gets its name from the fact that the
finished welds look like small roses.
rosin. A reddish-brown, translucent material left in the process of distilling turpentine from the sap of pine
trees. Rosin is used in the manufacture of paints, inks, adhesives, and as a flux for soldering.
rosin-core solder. A type of solder used for electrical and electronic work. Rosin-core solder is made in the
form of a hollow metal wire, filled with rosin. When the solder melts, the rosin flows out to cover the metal
and keep oxygen away from the surface, preventing the formation of oxides. Solder using synthetic rosin
for the core is called resin-core solder.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 497
rosin joint (bad solder connection). The common term for a bad connection made when soldering
electrical wires. Rosin core or resin core solder is used for this type of work, and it is possible for the
melted flux to hold the wires together without the solder wetting the wires and making a secure joint. A
rosin joint can be prevented by having the wires perfectly clean, and hot enough to melt the solder before
the solder is allowed to touch the wires.
rotable parts (maintenance supply). High usage, locally repairable components such as aircraft wheels,
tires, avionics assemblies, propellers, and built-up engines.
rotary actuator. A fluid-power actuator whose output is rotary movement. A hydraulic motor is a rotary
actuator.
rotary radial engine. A form of reciprocating engine used in some early airplanes because of its light
weight. In a rotary radial engine, the crankshaft is attached to the airframe and the crankcase, cylinders, and
propeller rotate. Rotary radial engines were popular up through World War I.
rotary switch. An electrical switch capable of selecting any of several circuits. Contacts around the
periphery of an insulating wafer connect to all of the circuits to be selected. The common lead is connected
to a wiper that makes connection with the contacts, one at a time. This wiper is turned by a shaft through
the center of the wafer. By turning the shaft, the wiper is moved to complete the selected circuit Rotary
switches may have several wafers stacked on one shaft to control several circuits at the same time.
rotation. That portion of the takeoff of an airplane equipped with a tricycle landing gear in which the
airplane has gained enough speed for the nose wheel to be lifted to increase the angle of attack and thus the
lift. The rotation speed is identified as the VR speed.
rotometer. A form of flow measuring instrument. A rotometer is made of a tapered glass tube holding a
metal indicator float. The fluid whose flow rate is to be measured enters the bottom of the rotometer and
flows upward, lifting the float. The taper inside the tube causes the pressure drop across the rotometer to
remain constant as the rate of flow changes. Rotometers can be used to measure the flow rate of either
gases or liquids.
rotor (axial-flow compressor component). The moving part of an axial-flow compressor. The rotor is
made of a series of disks, containing the compressor blades, that rotate between stages of fixed stator vanes.
Air is moved through the engine by the aerodynamic action of the rotor blades.
rotor (DC alternator component). The rotating component in a DC alternator. The rotor contains a field
coil mounted between two hard steel plates with interlacing fingers around their periphery. These fingers
form the poles for the rotating magnetic field. Excitation current is fed into the field coil through brushes
riding on two smooth slip rings.
rotor brake (helicopter rotor component). A brake used to stop the rotation of the rotor when a
helicopter is being shut down. The rotor brake may be actuated by either a mechanical or a hydraulic
mechanism.
rotor cloud (meteorology). A turbulent cloud formation found on the lee of some large mountain barriers.
The air in the cloud rotates about an axis parallel to the range, and rotor clouds indicate the possibility of
violent turbulence.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 498
rotorcraft. A heavier-than-air aircraft whose aerodynamic lift is produced by a set of rotating airfoils
called rotors. Helicopters and autogiros are types of rotorcraft. 14 CFR Part 1: “A heavier-than-air aircraft
　
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