Thermalling Best Practices
Air that rises faster than our gliders sink is what turns a mere descent into soaring flight. Whether knocking around the airport or stretching out on a cross country flight, the ability to find rising air and make the most of it is essential to mastery in the sky.
Warm air rising from the ground in a thermal is the most ubiquitous form of lift and the glider pilot’s most direct use of solar energy.
When locating and utilizing thermals for soaring flight, called thermalling, glider pilots must constantly be aware of any nearby lift indicators. Successful thermalling requires several steps: locating the thermal, entering the thermal, centering the thermal, and finally leaving the thermal. Keep in mind that every thermal is unique in terms of size, shape, and strength.
Mike Opitz: "Look where your high wing points towards (off in the distance) when you are in the best average lift of the circle. The next time around, that is the direction to correct towards. Conversely, when you are in the worst part, the low wing will point towards the direction to correct in. The shallowing /steepening only works if you are pretty close to centered anyway. If you are half in /half out, with the best part of your circle still short of being in the core, the shallowing out principle will never get you there if you wait for the vario to show lift".
Often stronger lift exists on one side of the thermal than on the other, or perhaps the thermal is small enough that lift exists on one side and sink on the other, thereby preventing a climb. There are several techniques and variations to centering.
One method involves paying close attention to where the thermal is strongest, for instance, toward the northeast or toward some feature on the ground. To help judge this, note what is under the high wing when in the best lift. On the next turn, adjust the circle by either straightening or shallowing the turn toward the stronger lift. Anticipate things a bit and begin rolling out about 30?before actually heading towards the strongest part. This allows rolling back toward the strongest part of the thermal rather than fly-ing through the strongest lift and again turning away from the thermal center. Gusts within the thermal can cause airspeed indicator variations; therefore, avoid “chasing the ASI.” Paying attention to the nose attitude helps pilots keep their focus outside the cockpit. How long a glider remains shallow or straight depends on the size of the thermal.
Credits:
Mike Opitz and:
http://www.pilotoutlook.com/glider_flying/thermal_soaring
http://www.gliderpilot.org/Thermal
