航空術(shù)語詞典 Dictionary of Aeronautical Terms 上

時(shí)間：2011-03-11 23:11來源：藍(lán)天飛行翻譯 作者：admin 點(diǎn)擊：次

crystal filter (electronic circuit). An electronic filter which opposes a certain band of frequencies, but allows all frequencies on either side of the band to pass. A crystal filter attenuates, or decreases the value of, AC signals whose frequencies are near the resonant frequency of the crystal in the filter circuit.
crystalline (physical structure). A type of molecular structure in which the molecules of a material are arranged in a definite pattern throughout the material. This pattern of molecular arrangement is called a crystal lattice.
crystal microphone (aircraft radio component). A microphone used for aircraft radio transmissions in which sound pressure waves distort a piece of piezoelectric crystal.
A diaphragm in the microphone is attached to a crystal of Rochelle salt or other piezoelectric material in such a way that, when sound waves vibrate the diaphragm, it distorts the crystal.
When the crystal vibrates, it produces a voltage across two of its opposite faces that changes in exactly the same way the sound pressure changes.
crystal oscillator. See crystal-controlled oscillator.
crystal oven. A device inside a piece of sensitive electronic equipment that holds the temperature of a frequency-controlling crystal constant.
The crystal is kept at a constant temperature inside the oven to prevent change in its physical characteristics and thus in the frequency of the alternating current it produces.
crystal transducer. A device that uses a piezoelectric crystal to change mechanical pressure or vibrations into electrical signals. When a piezoelectric crystal is physically distorted, a potential difference is created across its faces.
Crystal transducers are also called piezoelectric transducers.
CSD (constant-speed drive). A component used with either aircraft gas turbine or reciprocating engines to drive AC generators. The speed of the output shaft of the CSD is held constant while the speed of its input shaft varies.
The CSD holds the speed of the generator constant and thus the frequency of the AC it produces, as the engine speed varies through its normal operating range.
CTAF (common traffic advisory frequency). A frequency designated for the purpose of carrying out airport advisory practices while operating to or from an uncontrolled airport. The CTAF may be a UNICOM, MULTICOM, FSS, or tower frequency, and it is identified in the appropriate aeronautical publications.
CTF (centrifugal twisting force). The force acting about the longitudinal axis of a propeller blade which tries to rotate the blade to a low-pitch angle. See CTM.
CTM (centrifugal twisting moment). The force moment, acting about the longitudinal axis of a propeller blade, which tries to rotate the blade toward a low-pitch angle. As the engine rotates the propeller, centrifugal force tries to flatten the blade so all of its mass rotates in the same plane.
Centrifugal twisting moment (CTM) opposes aerodynamic twisting moment (ATM), but normally CTM is the greater. The resultant of these two twisting moments is a force on a rotating propeller that tries to move the blades toward a low-pitch angle.

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