時(shí)間：2011-03-11 23:11來源：藍(lán)天飛行翻譯 作者：admin 點(diǎn)擊：次
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Barographs are often sealed and are carried aloft to make a permanent record of the altitude that has been reached by the aircraft. barometer (pressure measuring instrument). An instrument used to measure the absolute pressure of the atmosphere. A mercury barometer measures the atmospheric pressure by the height of a column of mercury held up in a tube by the pressure of the atmosphere. An aneroid (no liquid) barometer measures the pressure by the amount an evacuated bellows is collapsed by the atmospheric pressure. barometric altimeter. A pneumatic altimeter. See pneumatic altimeter. barometric pressure. The pressure produced on the surface of the earth by the weight of the surrounding air. Barometric pressure is normally measured in inches of mercury, absolute. barometric scale. A scale on the dial of a sensitive pneumatic altimeter to which the pilot sets the barometric pressure level from which the altitude shown on the altimeter is measured. When the scale is set to the standard sea level pressure of 29.92 inches of mercury, the altimeter indicates pressure altitude. When it is set to the existing altimeter setting, the altimeter reads indicated altitude. barometric tendency (meteorology). The change of barometric pressure within a specified period of time. For aviation weather observations, the time period is normally three hours. barrage balloon. A tethered, gas-filled balloon used during wartime to protect an area from low-flying airplanes. An airplane is prevented from making a strafing run in an area protected by barrage balloons by the danger of flying into the tethering cables. barrel roll (airplane flight maneuver). A flight maneuver of an airplane in which the airplane rolls around its longitudinal axis. The term barrel roll has been replaced in modern usage; the maneuver is now called an aileron roll, or slow roll. barrier voltage (semiconductor parameter). The voltage across a forward-biased PN junction in a semiconductor diode or transistor. When the mobile charges are drawn away from the junction, ionic charges are left. These ionic charges cause a voltage, or potential difference, to exist across the junction. The positive barrier voltage is in the N-material, and the negative barrier voltage is in the P-material. The barrier voltage across the junction in a silicon diode is about 0.7 volt, and approximately 0.3 volt in a germanium diode. base (mathematics). The number in an exponential expression that is multiplied by itself the number of times shown by the exponent. baseball stitch. A type of hand stitch used to join two pieces of fabric that butt together, but do not overlap. Baseball stitches are used to sew together the edges of a tear in the fabric used to cover an aircraft structure. The baseball stitch gets its name from this type of stitch being used to sew the cover on a baseball. |
