RFI (radio-frequency interference). Interference with the operation of radios, televisions, and other types of electronic equipment caused by electromagnetic radiation. RFI is caused by spurious (unwanted and unintentional) radiation of electromagnetic energy. Improperly filtered amateur radio transmitters, radio-frequency electrical heaters, and certain types of medical equipment cause radio-frequency interference.
rheostat (electrical component). A variable resistor having two connections to install it in a circuit. The resistance element of a rheostat is made either of wire wound on a circular insulating card or of a carbon compound molded onto a disk. A wiper moves across the resistance element to change the amount of resistance put into the circuit.
A rheostat is similar to a potentiometer except that the potentiometer has three connections rather than two.
RHI (range-height indicator) scope (radar meteorology). A radar indicator scope that displays a vertical cross section of targets along a selected azimuth.
rhomboid. A plain, four-sided, closed figure in which the opposite sides are parallel, and the adjacent sides have different lengths. None of the angles in a rhomboid are right angles (90° angles).
rhumb line (navigation). A line drawn on a navigational chart that crosses all the meridians of longitude at the same angle.
rib (aircraft structure). The part of an aircraft wing structure that gives the wing its aerodynamic cross section. Sheet metal or fabric covers the ribs and gives the wing its airfoil shape.
ribbon direction (honeycomb material). The direction in a piece of honeycomb material that is parallel to the length of the strips of material that make up the core.
ribbon parachute. A parachute whose canopy is made of a series of cloth tapes that resemble ribbons. A ribbon parachute has less opening shock than a solid-canopy parachute because of the air escaping between the ribbons.
rib lacing. See rib stitching.
rib stitching (aircraft fabric covering). A method of attaching fabric to the structure of an aircraft by sewing it with a strong waxed string called rib-stitching cord. The cord is passed around the wing ribs, through the top and bottom fabric, and over a reinforcing tape. Each stitch is locked with a modified seine knot.
rib tread (tire tread). A series of circumferential grooves cut into the tread of a tire. A rib tread pattern provides superior traction and directional stability on hard-surfaced runways.
rich flameout (gas turbine engine operation). A condition in which the flame in a gas turbine engine goes out because of an overly rich fuel-air mixture. For fuel to burn in a turbine engine, it must be mixed with air in a ratio of between 8 and 18 parts of air for 1 part of fuel, by weight. If there is either more fuel or more air than this in the mixture, the flame will go out.
rich mixture (fuel-air mixture). An air-fuel mixture that contains less than 15 parts of air to 1 part of fuel, by weight.
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