Originally Posted by
scifi
Hi D.D... you are quite correct the VSI is a very sensitive instrument. The most likely reason is that it uses 0.45 litres of air in the capacity flask, as opposed to the maybe 10 cc of air in the aneroid capsules of an Altimeter; a factor of x 45 more possible sensitivity.
Yesterday when it was very blustery outside, my vario was moving about even in the house, in tune with the gusts of wind.
Not quite a straight comparison - a light aircraft VSI and a vario are subtly different. A VSI works on the principle of lag, ie showing the difference between the current static pressure and the static pressure some seconds ago. Depending on the manufacturer this may be a lag of 4-8 seconds. They are therefore reasonably useless at showing instantaneous changes, but OK at showing a steady state eg continuous climbs/descents. Most useful in a light aircraft during instrument approaches when visual cues are lacking.