Variometers

Vane type variometer measure the change in air pressure inherent to changes in altitude. The instrument consists of a cylindrical chamber with a precision-fit baffle (vane) rotating on shockproof jewel bearings and centered by a coil spring. The vane divides the chamber in two: one section is open to static pressure, while the other is connected to an expansion tank, in which a volume of air is insulated against the thermal effects. Differences in pressure are compensated by the narrow gap between vane and chamber wall. There is a change in static pressure when an aircraft climbs or descends, and a differential pressure is established between the tow sections of the chamber.

The resultant defection of the vane provides a measure of the vertical speed and this deflections is transferred to the pointer of the instrument. The response rate of a variometer is important. In high performance gliding, up-currents can be identified all the quicker and used all the more efficiently if the variometer responds without delay. Defined as the length of time the instrument takes to reach 65 % of its final reading in response to a sudden change in vertical speed, the time constant serves as a standard for gauging speed of response. The faster a variometer responds, the smaller is its time constant.

Table variometers incl. EASA Form One
Table variometers without EASA Form One
Scale drawing
Detailed pictures

Installation and maintenance 5 StV, 5 StVM, 5 StVL und 5 StVLM