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weather conditions by measuring the amount and intensity of static electrical discharges within the storm.
STOVL (Short TakeOff and Vertical Landing). STOVL performance of an aircraft is the ability of the
aircraft to take off and clear a 50-foot obstruction in a distance of 1,500 feet from the beginning of the
takeoff run. The aircraft can land vertically, with no forward speed.
straightedge. A bar, or a piece of metal, wood, or plastic, used to check another piece of material or
surface for straightness, or used to draw straight lines. A straightedge is similar to a ruler, except a
straightedge does not have graduations marked on it.
straight-in IFR approach (air traffic control). An instrument approach in which the final approach is
begun without first executing a procedure turn. A straight-in approach is not necessarily completed with a
straight-in landing, nor is it made to straight-in landing minimums.
straight-in VFR approach (air traffic control). An entry into an airport traffic pattern by intercepting the
extended runway center line without executing any other portion of the traffic pattern.
straight-peen hammer. A type of hand-held hammer used for forming sheet metal. One end of the head is
round and has a flat face. The other end is wedge-shaped, with the apex (peak) of the wedge parallel to the
handle. A cross peen hammer is much like a straight peen hammer except the wedge on its head is
perpendicular to the handle.
straight-polarity arc welding. DC electric arc welding in which the electrode is negative with respect to
the work.
straight-run gasoline (petroleum product). Gasoline refined from crude oil without the addition of any of
the additives used in some of the other methods of refining.
straight-through combustor (turbine engine component). A combustor in a gas turbine engine through
which the air from the compressor to the turbine flows in an essentially straight line.
strain. A deformation, or physical change, in a material caused by a stress. According to Hooke’s law, the
strain in a material, the amount it stretches or compresses, is directly proportional to the stress, until the
elastic limit of the material is reached. Spring scales and certain types of torque wrenches work on the
principle that strain is proportional to stress.
strain gage. A device attached to the surface of a piece of equipment to measure the amount of strain
acting on the surface. A strain gage is a piece of extremely fine wire bonded (glued) to the surface, with the
length of the wire parallel to direction of the strain to be measured. When the surface is stressed, it is also
strained (deformed), and it either stretches or compresses. Since the strain gage is bonded to the surface, it
also stretches or compresses.
The resistance of the strain gage is measured with a precision bridge-type instrument, and the
resistance change caused by the wire stretching or compressing is measured. Strain gages are calibrated so
the change in resistance indicates the amount of strain acting on the surface.
strain hardening (metallurgy). A method of hardening metals that cannot be hardened by heat treatment.
Copper, some aluminum alloys, and low-carbon steel cannot be hardened by heat treatment, but they can be
hammered, rolled, pulled, or bent to change their grain structure enough that they become hard.
stranded wire (electrical conductor). An electrical conductor made up of a number of small wires. These
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 560
wires are either twisted together or braided and are usually enclosed in an insulating material. A stranded
wire is often called a cable.
stratiform clouds (meteorology). Clouds that form in stable air and appear to be in layers. Stratus clouds,
stratocumulus, and nimbostratus clouds are all stratiform clouds.
stratocumulus (meteorology). Low clouds that are predominantly stratiform in nature. Stratocumulus
clouds are gray with some dark parts and often with white patches.
stratosphere. The upper part of earth’s atmosphere. The stratosphere extends upward from the tropopause,
which is about seven miles (11 kilometers) above the surface of the earth, to an altitude of about 22 miles
(35 kilometers). The temperature of the air in the stratosphere remains constant at –56.5°C (–69.7°F), and
since there is no water vapor in the stratosphere, there are no clouds, nor any of the weather conditions that
exist at the lower altitudes.
stratus (meteorology). A low, gray cloud layer or sheet with a fairly uniform base. Stratus clouds
sometimes appear in ragged patches. They seldom produce precipitation but may produce drizzle or snow
grains.
streamlined body. A body whose shape is such that fluid moving over it flows in smooth lines with no
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