what is density or pressure Altitude? Density or pressure altitude It is the altitude relative to the standard atmosphere conditions (ISA) at which the air density would be equal to the indicated air density at the place of observation. In other words, density altitude is air density given as a height above mean sea level. Density altitude can also be considered to be the pressure altitude adjusted for non-standard temperature. Both an increase in temperature, decrease in atmospheric pressure, and, to a much lesser degree, increase in humidity will cause an increase in density altitude. In hot and humid conditions, the density altitude at a particular location may be significantly higher than the true altitude. In aviation the density altitude is used to assess the aircrafts aerodynamic performance under certain weather conditions. The lift generated by the aircraft and the relation between indicated and true airspeed is also subject to air density changes. Furthermore, the power delivered by the aircraft engine is affected by the air density and air composition.In aviation, pressure altitudeis the indicated altitude when an altimeter is set to an agreed baseline pressure setting. The baseline pressure is 1013.25 hPa, equivalent to 1013.25 millibar, or 29.92 inches of mercury. This setting is equivalent to the air pressure at mean sea level (MSL) in the International Standard Atmosphere (ISA). Pressure altitude is primarily used in aircraft performance calculations and in high-altitude flight (above the transition altitude). The term QNE refers to the indicated altitude when 1013.2mb/29.92 inHg is set in the altimeters Kollsman window and not the setting itself, as is commonly misconceived. Aircraft transponders report the pressure altitude; corrections for atmospheric pressure variations are applied on the ground.The relationship between static pressure and pressure altitude is defined in terms of the properties of the International Standard Atmosphere. HOW TO CALCULATE THE PRESSURE ALTITUDE? For every millibar, pressure altitude changes by approximately 30 feet. For every inch of mercury, the pressure altitude changes by approximately 1000 feet. So for example: The atmospheric pressure is 1034 millibar so what will be the pressure altitude. 1034 mb is equal to 30.53 Hg (33.8363 mb per =1 Hg) So, 30.53 - 29.92 = 0.61 correction factor. Since 30.53 is higher than standard (29.92), the pressure altitude will be lower than field elevation. Pressure altitude is the altitude corrected to standard pressure - if you set your altimeter to 29.92, you will be reading pressure altitude 0.61 X 1000 ft/Hg = 610 ft lower 2340- 610 = 1730 Pressure altitude2
Posted on: Fri, 14 Mar 2014 07:45:08 +0000