时间:2011-04-05 11:32来源:蓝天飞行翻译 作者:航空 点击:次
To view this page ensure that Adobe Flash Player version 9.0.124 or greater is installed. and pressure altitude must be clearly understood. True altitude means the vertical height above mean sea level and is displayed on the altimeter when the altimeter is correctly adjusted to the local setting. For example, if the local altimeter setting is 30.12 in. Hg., and the altimeter is adjusted to this value, the altimeter indicates exact height above sea level. However, this does not reflect conditions found at this height under standard conditions. Since the altimeter setting is more than 29.92 in. Hg., the air in this example has a higher pressure, and is more compressed, indicative of the air found at a lower altitude. Therefore, the pressure altitude is lower than the actual height above mean sea level. To calculate pressure altitude without the use of an altimeter, remember that the pressure decreases approximately 1 inch of mercury for every 1,000-foot increase in altitude. For example, if the current local altimeter setting at a 4,000-foot elevation is 30.42, the pressure altitude would be 3,500 feet. (30.42 – 29.92 = .50 in. Hg. 3 1,000 feet = 500 feet. Subtracting 500 feet from 4,000 equals 3,500 feet). The four factors that most affect density altitude are: atmospheric pressure, altitude, temperature, and the moisture content of the air. ATMOSPHERIC PRESSURE Due to changing weather conditions, atmospheric pressure at a given location changes from day to day. If the pressure is lower, the air is less dense. This means a higher density altitude and less helicopter performance. Pressure Altitude—The height above the standard pressure level of 29.92 in. Hg. It is obtained by setting 29.92 in the barometric pressure window and reading the altimeter. True Altitude—The actual height of an object above mean sea level. ALTITUDE |