aviation Aviation includes the activities surrounding mechanical flight and the aircraft industry. ''Aircraft'' includes fixed-wing and rotary-wing types, morphable wings, wing-less lifting bodies, as well as lighter-than-air craft such as hot air ...

, and particularly in the sport of

gliding Gliding is a recreational activity and competitive air sport in which pilots fly unpowered aircraft known as gliders or sailplanes using naturally occurring currents of rising air in the atmosphere to remain airborne. The word ''soaring'' is al ...

, a stick thermal is an illusion that the glider is climbing in a

thermal A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...

when, in fact, the upward movement of the glider is caused by nothing more than the pilot pulling backwards on the control stick, causing the aircraft to climb, but lose airspeed.Glider Flying Handbook
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Background

It is useful for a pilot to know the rate of climb of air in a thermal. They can use this to find the strongest area of lift in the thermal. A

variometer 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 in ...

can be used to measure the rate of ascent of an aircraft. However, a simple variometer does not actually measure the lift in the thermal, it measures the rate of ascent of the aircraft. So a pilot may be inside a thermal that is moving upwards at 2 metres per second, but the pilot may be diving their aircraft at 2 metres per second. So the variometer shows zero rate of climb, and does not indicate the presence of the thermal. A total energy compensated variometer will show the actual rate of climb of the thermal, regardless of the movement of the aircraft.

Notes

Gliding technology {{Air-sports-stub