quotient (mathematics). The answer found when one number is divided by another.
R
rabbet. A groove cut near the edge of a piece of wood that allows another piece to fit into it to form a joint.
rabbet plane. A woodworking plane whose blade extends to the outside edge of the body of the plane. A rabbet plane is used to cut a rabbet (groove) in the face of a piece of wood.
race (bearing). A hardened and polished steel surface on which antifriction bearings roll. The races for ball bearings are grooves. For tapered roller bearings, the races are cones, and for needle bearings, the races are flat rings.
rack-and-pinion (gear arrangement). An arrangement of gears in which rotary motion of the pinion (a small spur gear) is changed into linear motion of the rack. The rack is a straight piece of metal with teeth cut into one of its sides. The teeth of the pinion mesh with the teeth of the rack, and as the pinion rotates, it moves the rack. The rack and pinion may also be designed in such a way that movement of the rack rotates 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 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.