Editing Variometer (section)

{{Short description|Flight instrument which determines the aircraft's vertical velocity (rate of descent/climb)}}
{{about|the flight instrument|the variable transformer|Transformer types#Variometer and variocoupler| the instrument for measuring a magnetic field|Magnetometer}}

In [[aviation]], a '''variometer''' – also known as a '''rate of climb and descent indicator''' ('''RCDI'''), '''rate-of-climb indicator''', '''vertical speed indicator''' ('''VSI'''), or '''vertical velocity indicator''' ('''VVI''') – is one of the [[flight instruments]] in an [[aircraft]] used to inform the [[aviator|pilot]] of the [[rate of descent or climb]].<ref name=FAA07>[[Federal Aviation Administration]], ''Glider Flying Handbook'', Skyhorse Publishing Inc., 2007
{{ISBN|1-60239-061-4}} pages 4-7 and 4-8</ref>  It can be calibrated in [[metres per second]], [[feet per minute]] (1&nbsp;ft/min = 0.00508&nbsp;m/s) or [[knot (unit)|knots]] (1&nbsp;kn ≈ 0.514&nbsp;m/s), depending on country and type of aircraft.  It is typically connected to the aircraft's external [[static pressure]] source.

In [[powered flight]], the pilot makes frequent use of the VSI to ascertain that level flight is being maintained, especially during turning maneuvers. In [[gliding]], the instrument is used almost continuously during normal flight, often with an audible output, to inform the pilot of [[Atmospheric convection|rising or sinking air]]. It is usual for gliders to be equipped with more than one type of variometer. The simpler type does not need an external source of power and can therefore be relied upon to function regardless of whether a battery or power source has been fitted. The electronic type with audio needs a power source to be operative during the flight. The instrument is of little interest during launching and landing, with the exception of [[aerotow]], where the pilot will usually want to avoid releasing in sink.

[[Image:R22-VSI.jpg|thumb|The vertical speed indicator from a [[Robinson R22]].  This is the most common type used in [[aircraft]], showing vertical speed in feet per minute (ft/min).]]
[[File:Diaphragm Variometer.jpg|thumb|Diaphragm Variometer operation]]