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Altimetry : pressure converter by Azzurro Articles |
hPa convertion <-> inches Hg and pressure calculation QNH - QFE
The altimeter is one of the essential instruments in an aircraft, besides it is often installed in double, even on very basic aircraft. According to the flight phase, it can be adjusted according to the pressure "in level of the sea", or in "airfield altitude", or in "standard pressure" (*).
You will find explanations more detailed on the weather sites or in doing a search on the web.
The countries having adopted the metric system calculate the pressures in hectoPascals (hPa).
But certain countries, in particular Anglo-Saxons, calculate still in inches. Their altimeters are graduated in "inches of mercury" or "inches Hg", Hg being the chemical symbol of the mercury. It is the case of our aircraft, in Fly!.
How not to get mixed up ? Well here is a little converter very simple, adapted according to the converter online of Meteo
Suisse.
In order to the convertion can be made, you must :
- choose either the hPa (orange boxes), or the inches (yellow boxes),
- fill the two first lines, only one box by line,
these are the QNH (pressure for the level of the sea, provided by the ATIS), and the altitude-pressure of the airfield provided by the VAC maps (for example 69 hPa for Gap-LFNA),
- use the point and not the comma to separe the decimal digits (and don't forget the zero ahead if necessary),
- then click on "calculate"
to obtain the QFE (pressure at the altitude of the airfield), and all the values in the two measure systems.
In case of numerous calculations, click on "reset" before doing a new operation.
To note : it is not possible to enter a value in metres or in feet and to tranform it in "pressure". Indeed, it is not a simple ratio like the "rule of three", the impact of the pressure decreasing when the altitude increases.