delta connection (electrical wiring connection). A type of connection used for three-phase alternating-current generators, motors, and transformers. Two of the phase windings are in series, across the third phase winding.
The term delta connection comes from the symbol for this type of connection, which is drawn in such a way that it shows the windings arranged in the form of a triangle, or delta. The current flowing between any two leads in a delta-connected circuit is 1.73 times the current flowing in any single winding.
delta hinge (helicopter rotor hinge). A hinge at the root of a helicopter rotor blade. The axis of the delta hinge lies in the plane of rotation of the blade, and allows the blade to flap up or down to equalize the lift produced by the rotor system as the helicopter moves through the air.
delta iron. The molecular arrangement in iron at temperatures between 1,392°C and 1,538°C. Pure iron melts at 1,538°C.
Δ P (delta P). Differential pressure.
delta wing (airplane wing configuration). A wing having a triangular shape — an extreme amount of sweepback on the leading edge and a trailing edge that is almost perpendicular to the longitudinal axis of the airplane. Delta wings are used on some supersonic airplanes.
demagnetize. To remove the magnetism from a piece of magnetized material. When a piece of material is magnetized, all the magnetic domains are aligned, or oriented in the same direction. When it is demagnetized, the magnetic domains are knocked out of alignment, and their magnetic fields cancel so there is no overall magnetic field.
demand oxygen system (breathing oxygen system). An oxygen system installed in an aircraft and used by the flight crew when flying at high altitude. The demand system meters oxygen from the regulator to the mask only when the user inhales, and the flow of oxygen is shut off during exhale.
A demand oxygen system is much more economical of the oxygen supply than a continuous-flow system.
demodulate (telecommunications). To remove the modulation from a telecommunicated signal.
When computer data is transmitted by telecommunications, it is changed into audible tones, or modulated, so it will pass it over the telephone lines. At the receiving computer, the data is demodulated (the modulation is removed), and the data is changed back into its digital form.
demodulation (radio signal). The production inside a radio receiver of an audio-frequency AC signal that follows the modulation on a radio-frequency carrier. Audio-frequency information or music is used to change the amplitude or frequency of the RF carrier wave in the radio transmitter.
When the modulated carrier is picked up by the receiver, it is demodulated. Changes in the amplitude or frequency of the carrier produce an audio-frequency AC that follows these changes.
demulsibility. The ability of an oil-water emulsion to separate into its components of water and oil.
demulsifier. A chemical, physical, or electrical system that either breaks down a liquid-in-liquid emulsion or keeps such an emulsion from forming.
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