Glossary - S

Schematic diagram.   A diagram that locates components with respect to each other within a system.

Scientific notation.   Used as a type of shorthand to express very large or very small numbers. For example, to express 1,250,000,000,000 in scientific notation is 1.25 × 1012.

Sea level pressure.   The atmospheric pressure at sea level. Average sea level pressure is 29.92 inches of mercury, or 1013.25 millibars.

Sectional view.   A view obtained by cutting away part of an object to show the shape and construction at the cutting plane.

Semiconductor.   Any device based on either preferred conduction through a solid in one direction, as in rectifiers, or on a variation in conduction characteristics through a partially conductive material, as in a transistor.

Series circuit.   The most basic electrical circuit in which there is only one possible path for current to flow. Current must pass through the circuit components, the battery and the resistor, one after the other, or “in series."

Series-parallel DC circuits.   A grouping of parallel resistors connected in series with other resistors.

Signed numbers.   A signed number can be either a positive or negative number. A positive number is a number that is greater than zero. A negative number is a number that is less than zero.

Sine.   A trigonometric function comparing two sides of a right triangle as follows: Sine = opposite side hypotenuse

Sine wave.   A continuous waveform with a constant frequency and amplitude.

Sketch.   A simple rough drawing that is made rapidly and without much detail.

Slide caliper.   Often used to measure the length of an object. It provides greater accuracy than a ruler.

Solenoid.   A loop of wire, often wrapped around a metal core, which produces a magnetic field when an electrical current is passed through it.

Specific gravity.   The ratio of the mass of a solid or liquid to the mass of an equal volume of water.

Specific heat.   The quantity of heat necessary to increase the temperature of a unit of the mass of a substance 1 °C. The specific heat of a substance is the ratio of its specific heat capacity to the specific heat capacity of water.

Speed of sound.   The speed of sound at sea level under standard temperature and pressure conditions is 1,108 feet per second or 658 knots.

Spirit level.   A leveling instrument placed on or against a specified place on the aircraft. Spirit levels have vials that are full of liquid, except for a small air bubble. When the air bubble is centered between the two black lines, a level condition is indicated.

Square root.   A non-negative number that must be multiplied by itself to equal a given number.

Standard empty weight.   The weight of the airframe, engines, all permanently installed equipment, and unusable fuel. Depending upon the part of the Federal regulations under which the aircraft was certificated, either the undrainable oil or full reservoir of oil is included.

Standard weights.   Values used in weight and balance calculations if specific weight for an item is unknown. The following are examples:

• Aviation gasoline          6 pounds per gallon
• Crew and passengers    170 pounds per person
• Lubricating oil              7.5 pounds per gallon
• Turbine fuel                 6.7 pounds per gallon
• Water                         8.35 pounds per gallon

Static stability.  The initial response that an airplane displays after its equilibrium is disrupted.

Strain.   A deformity or change in an object due to stress.

Stress corrosion.   Occurs as the result of the combined effect of sustained tensile stresses and a corrosive environment.

Stress.   The internal resistance of an object to external forces attempting to strain or deform that object. Measured in pounds per square foot or pounds per square inch (psi).

Subtraction.   The process where the value of one number is taken from the value of another.