Stick thermal
 | This article relies largely or entirely on a single source. (April 2013) |
In aviation, and particularly in the sport of gliding, a stick thermal is an illusion that the glider is climbing in a thermal 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.
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 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.
A stick thermal is where an uncompensated variometer indicates that an aircraft is ascending or descending due to pilot input (the joystick).[1]
The pilot may believe he is in a thermal as the variometer indicates that he is ascending, but in fact he is ascending due to his own control of the aircraft.