rime ice. A type of ice which forms on an aircraft flying through visible moisture (as in a cloud) when the air temperature is below freezing. Rime ice is made of ice crystals and is rough and milky looking. Rime ice not only adds weight to the aircraft, but since it is rough, it disturbs the airflow over the wing and tail surfaces and destroys lift.
ring cowl (reciprocating engine cowling). A type of cowling used to cover an aircraft radial engine. A ring cowl surrounds the cylinder heads and decreases the aerodynamic drag caused by the cylinders and improves the flow of cooling air through the cylinder fins. Ring cowls are also called speed rings, or more properly, Townend rings, after their inventor, English physicist H.L. Townend. See illustration for Townend ring.
ring gear. One of the gears in a planetary gear system. The teeth are on the inside of the ring gear, and the planetary gears mounted on pins fastened to the spider-like output shaft mesh with and ride between the inside the ring gear and the outside of the sun gear. The ring gear can be either rigidly mounted in the gear housing, or it can be driven by the input shaft, depending upon the gear ratio of the system. If the ring gear is rigidly mounted, the sun gear is driven by the input shaft.
ringworms (fabric defect). A series of circular cracks in the dope film on a fabric-covered aircraft. Ringworms appear when a blunt object presses against the fabric that is covered with a dope film that has become brittle because its plasticizers have dried out. Ringworms can be removed by rejuvenating the dope. See rejuvenation.
rip panel (free balloon component). A panel in the gas bag of a free balloon that can be opened by pulling the rip cord to dump gas from the balloon.
ripple filter (electronic filter). An electronic filter installed in a DC power supply. The ripple filter decreases the amplitude of the ripple remaining when alternating current is rectified.
ripple frequency. The frequency of the ripple in the output of a rectifier circuit. In a full-wave rectifier, the ripple frequency is twice the frequency of the alternating current. In a half-wave rectifier, the ripple frequency is the same as that of the AC.
ripsaw. A woodcutting saw with large, chisel-shaped teeth. A ripsaw is used to cut wood in the direction of its grain.
rise time (electrical pulses). The length of time (usually measured in picoseconds or nanoseconds) needed for the leading edge of an electrical pulse to rise from 10% to 90% of its final value. The rise time of a pulse relates to the steepness of the leading edge of the pulse.
rivet. A small pin-type fastener, used to fasten pieces of sheet metal together. Most aircraft rivets are made of aluminum alloy and are driven cold. The rivet is slipped through holes in the material being fastened, and a heavy steel bucking bar is held against the end of the shank. The head of the rivet is hammered with a rivet gun (an air hammer). The bucked head, or shop head, that is formed when the rivet is driven, is flat on top, and its sides are rounded.
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