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the cockpit is reached. This additional movement stretches the control mechanism, and when the throttle
control is released, it springs back a slight amount.
Technicians often refer to this type of control adjustment as “rigging in the proper cushion.”
Springback assures that the stop on the carburetor is contacted before the stop in the cockpit.
springback (sheet metal forming). Springback, in sheet metal forming, is the tendency of the metal to
spring back and form an angle less than the angle bent in a brake or a forming block. When a 90° angle is
to be bent, the metal must be bent through an angle of about 93° or 94° (depending upon the temper of the
metal) so it will spring back to exactly 90°.
spring steel. High-carbon steel, a steel containing more than 0.5% carbon, that has been hardened and
tempered to give it the maximum amount of elasticity, or the ability to return to its original shape after it
has been deflected. Spring steel is hardened and then tempered to remove part of the brittleness by
reheating until it turns a uniform dark blue.
spring tab (aircraft controls). A small auxiliary tab, set into the trailing edge of a primary control surface
on a high-speed airplane. The control surface is attached to the control horn through a torsion rod. Under
normal flight loads, the spring tab remains fixed to the control surface and serves no purpose. But, when the
air loads are high and a large amount of force is needed to move the control surface, the torsion rod twists,
and the control rod moves the spring tab in a direction opposite to that of the surface on which it is mounted.
It then acts as a servo tab and aids the pilot in moving the control surface. See servo tab.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 549
springwood. The lighter, softer part of the grain of wood. The heavier and darker part of the wood grain is
the summerwood. The cross section of a tree trunk contains a series of concentric rings, called annual rings.
Each ring is made up of a light and a dark area. The light area is the part of the tree that grew at a fast rate
in the spring of the year and is called the springwood. The dark area is the part of the tree that grew more
slowly during the summer of the year and is called summerwood.
sprue (casting). A hole in a mold through which liquid plastic or molten metal is poured to fill the mold.
When the molded material becomes solid, the mold is opened, and the metal which was in the sprue (this
metal is also called a sprue) is broken from the casting and discarded.
spur and pinion reduction gear system. A type of reduction gear system that allows one shaft to turn at a
speed slower than that of another shaft. A pinion is a small-diameter spur gear, whose teeth mesh with
those on the larger-diameter gear. The pinion turns faster than the larger gear, and it turns in the direction
opposite to that of the larger gear.
spur gear. A gear wheel with teeth radiating outward around its periphery. The term spur gear comes from
the fact that this type of gear looks much like the rowel, or toothed wheel, that was a part of the spur worn
by many of the early-day cowboys.
spur gear pump. A form of constant-displacement fluid pump that uses two meshing spur gears mounted
in a close-fitting housing. Fluid is taken into the housing where it fills the space between the teeth of the
gears and is carried around the housing as the gears rotate. On the discharge side of the pump, the teeth of
the two gears mesh, and the fluid is forced out of the pump.
squall (meteorology). A sudden increase in wind speed by at least 15 knots to a peak of 20 knots or more,
and lasting for at least one minute.
The essential difference between a gust, lasting less than one minute, and a squall is the duration
of the peak speed.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 550
squall line (meteorology). Any nonfrontal line or narrow band of active thunderstorms with or without
squalls.
square (geometric figure). A closed, plane (flat), four-sided figure. Each angle in a square is a right angle
(90°), all sides have the same length, and the opposite sides of a square are parallel.
square engine (reciprocating engine). A reciprocating engine whose bore and stroke have the same
dimensions.
The bore of the engine is the diameter of the cylinders, and the stroke is the distance the piston
moves from the top of its travel to the bottom.
square mil. A unit of area possessed by a square having sides of one mil, or one thousandth of an inch
(0.001 inch).
square of a number (mathematics). The product of a number multiplied by itself.
square root (mathematics). A number which, when multiplied by itself, will give a particular number.
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航空术语词典Dictionary of Aeronautical Terms 下(66)
