ALTITUDE EFFECT ON VARIOMETERS

Theory shows that mechanical variometers should indlcate something close to the true vertical velocity of the aircraft at all heights. Any errors are due to variations in the viscoslty of the alr at the internal leak or to temperature dlfferences between the alr passing through the leak and the air of the outside atmosphere. These effects could also lead to differing calibrations for climb and descent, since the state of the air flowing in from the atmosphere during a descent is not necessarily the same as that of the air flowing out from the capaclty during a climb, other things being equal. However, these effects can be mininized by suitable design and, for all practlcal purposes, a modern aeroplane rate-of-climb indicator may be assumed to show true vertical velocities in a standard atnosphere. Laboratory callbratlons of PZL sailplane varioneters also show slmilar characteristics although the laboratory conditions do not reproduce the proper atmospheric parameters. For the present purposes, it wiil be assumed that mechanical variometers do indeed show true vertical velocities assuming of course, accurate calibration at sea-level.