lock ring (safety device). A retaining ring used to prevent a shaft moving lengthwise out of a hole. A groove is cut around the outside of the shaft, and the spring steel lock ring grips the groove and holds the shaft in place.
A lock ring is made in the shape of an open circle, with tabs at both of its ends so a pair of special lock ring pliers can be used to expand the ring enough for it to slip over the shaft. When the ring is over the groove, the pliers are released, and the spring action of the lock ring holds it tight in the groove. Lock rings are made for both external and internal grooves.
lockstitch (aircraft fabric covering). A type of stitch used to prevent an entire hand-sewed seam loosening if the thread should break at any point. When making a sewed-in patch to aircraft fabric, the patch is sewed in using a baseball stitch. At every eight to ten stitches, the seam is locked with a modified seine knot.
lock tab (mechanical locking device). A type of mechanical lock, used to prevent a nut from loosening on a shaft. A locking hole or keyway is cut in the shaft and the internal tab on the lock ring is slipped into it. The nut is screwed down onto the shaft and tightened to the proper torque; then one or more of the external locking tabs are bent up against the flats of the nut to keep it from backing off and becoming loose.
lockwire. A term used for safety wire. Lockwire is soft brass, stainless steel, or galvanized low-carbon steel wire, used to safety fasteners so they will not loosen by vibration. Lockwire is passed through holes in the fasteners and twisted, then secured to a hole in an adjacent fastener or to a hole in the structure. Twisted lockwire should always pull on the fastener in the direction that tries to tighten it.
lodestone. A natural magnetic iron oxide. Lodestones were discovered in ancient times and were the first devices to be used as a magnetic compass. The term lodestone comes from “leading stone.”
log (record). A record kept of activities, with entries made as they occur. In the field of aviation, a log is kept by pilots to record flight time. A log is kept on every airframe, engine, propeller, and rotor, to show the amount of time in service and to record all the maintenance that has been done on each device.
logarithm. The exponent used to indicate the power to which a base number must be raised to obtain a
given number. In the expression 64 = 1,296, the base number is 6, and 4 is the power to which 6 must be raised to get 1,296. Four is the logarithm of 1,296 to the base 6.
logarithmic curve. A mathematical curve plotted in such a way that the coordinate of any point varies as the logarithm of the other coordinate.
Horizontal Vertical
coordinate coordinate
20 -----------------------------------------0
21 -----------------------------------------2
22 -----------------------------------------4
23 -----------------------------------------8
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