Variometer - definition
Variometer - definition
A variometer is an instrument used to measure the vertical rate of change in altitude, or the rate of ascent or descent of an aircraft, usually in metres per second (m/s) or Feet per minute (ft/min). It is an essential piece of equipment in aviation, particularly in gliders, where it plays a key role in assessing thermal conditions and flight dynamics.
The principle of the variometer is based on measuring changes in static atmospheric pressure, which decreases with increasing altitude. The classical variometer uses a sealed chamber with controlled airflow through a thin capillary or nozzle, resulting in a delayed response of the pressure inside the chamber relative to the external pressure. The pressure difference between inside and outside is proportional to the rate of change in altitude and is converted into a mechanical (pointer) or electrical signal.
Modern variometers, especially those used in sport and recreational aviation, can be equipped with electronic circuits, pressure sensors and microprocessors for a faster and more accurate response. They often incorporate an acoustic climb and descent indication function (known as an 'audio variometer'), allowing the pilot to keep track of changes without having to constantly look at the instruments. Electronic variometers can also integrate GPS data and interface with other navigation systems to create enhanced variometer systems with thermals analysis and route optimisation.
The variometer does not measure altitude directly, nor does it replace altimeter, but it does provide information on the dynamics of altitude change, which is particularly important when assessing air movements, planning a sailing flight or manoeuvring in turbulent conditions. For correct operation, it requires proper connection to a static pressure source and calibration according to the characteristics of the sensor used.
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