Shuttle valves are used in aircraft landing gear and brake systems to allow compressed air to be used to extend the landing gear or apply the brakes if the normal hydraulic system should fail.
SI. The universal abbreviation for the International System of Units. See International System of Units.
SID (Standard Instrument Departure) charts. Aeronautical charts designed to expedite clearance delivery and facilitate transition between takeoff and enroute operations.
sidebands (radio transmission). The bands of frequencies on either side of the carrier frequency in amplitude modulated (AM) radio transmission. The bandwidth of a transmitted radio signal includes the carrier frequency (the frequency produced by the oscillator in the transmitter) and the frequencies of both the lower and the upper sidebands.
The frequency of the lower sideband is the carrier frequency minus the highest audio frequency
used to modulate the carrier. The frequency of the upper sideband is the carrier frequency plus the highest audio frequency used to modulate the carrier.
side slip (airplane flight maneuver). A flight maneuver in which the airplane is banked while the rudder keeps it on a straight heading. This crossed-control condition causes the airplane to move sideways toward the low wing.
sidestep maneuver (air traffic control). A visual maneuver accomplished by a pilot at the completion of an instrument approach to permit a straight-in landing on a parallel runway not more than 1,200 feet to either side of the runway to which the instrument approach was conducted.
sidestick controller. A cockpit flight control used on some of the fly-by-wire equipped airplanes. The stick is mounted rigidly on the side console of the cockpit, and pressures exerted on the stick by the pilot produce electrical signals that are sent to the computer that flies the airplane.
sidetone (radio transmission). The audio-frequency signal fed back from the microphone of a radio transmitter into the earphones connected to the radio receiver. Sidetones allow a person to hear the signal as it is being transmitted.
siemens. A unit of electrical conductance. The siemens has replaced the older measurement called a mho. One siemens is the amount of electrical conductance that allows an electromotive force of one volt to move a flow of electrons of one ampere (one coulomb per second). One siemens is the reciprocal of one ohm.
sight glass (air conditioning system component). A small window in the high side of a vapor-cycle cooling system. Liquid refrigerant flows past the sight glass, and if the charge of refrigerant is low, bubbles will be seen. There are no bubbles in the refrigerant of a fully charged system.
sight glass (liquid-level indicator). A transparent tube on the outside of a reservoir or tank connected to the bottom of the container. The level of the liquid in the sight glass is the same as that in the container, and it gives a visual indication of the level of liquid in the reservoir.
|
