## Glider Performance During Thermal Soaring ### When Searching for Lift When [[Locating Thermals#Searching]] for thermals, a pilot wants to search a maximum area, or cover maximum distance, with a minimum loss of altitude. Best glide (L/Dmax) speed should be used, and corrected for the existing winds and sink. ### When Thermalling Once circling in a thermal, the pilot must select an appropriate speed and bank angle. Minimum sink speed, and a minimum bank angle would produce the best climbing performance, however, the best lift is often concentrated in a fairly narrow core. Steep banks of 45° or more are often needed to remain within the best lift. [[Correcting Performance Speeds]] should be applied to the minimum sink speed, or a higher speed if minimum sink speed does not provide adequate aircraft control. ## Entering a Thermal In addition to variometer trends, the first indications of entering a thermal are often the sensations of turbulence and sink encountered just outside of a thermal. ![[thermal horizontal structure.png]] As the pilot contacts the lift, a positive G load is experienced; the pilot should transition from L/D max to the appropriate minimum sink speed. A wing often rises, indicating the direction of the thermal; the pilot may elect to wait if stronger lift is expected, or immediately begin turning to use the thermal. In any case, [[Collision Avoidance During Thermal Soaring]] is paramount, so **ALWAYS visually clear the area before turning!** ## Centering a Thermal Rarely, the pilot rolls into the turn and is centered in the best lift within the thermal. Most of the time, the glider experiences stronger lift on one side of the turn, and weaker lift or sink on the other. The pilot will need to shift the circle to center on the best lift within the thermal. This is best accomplished while building a mental picture of the thermal, and visualizing the glider's position in relationship to the core. Constant changes will make this difficult or impossible; maintain a **consistent** speed and bank angle (**attitude**), and make **one** correction per circle. ![[GFH centering thermal.png]] This is perhaps mostly easily accomplished by noting where the lift is strongest, and shallowing the bank approximately 270° (3/4 turn) later to shift the circle in that direction. This can be accomplished by ground references, either straight ahead, or off of the wing of the glider. ![[GA centering thermal.png]] Other centering techniques include shallowing the bank as the greatest "surge" or positive G load is experienced, or shallowing the bank 60° after the minimum variometer indication to compensate for instrument lag. ![[GFH 270 correction.png]] If the pilot has turned the wrong direction and encounters sink, flying straight after 270° of turn can help to re-contact the thermal. ## Exiting a Thermal The pilot may leave the thermal when the top is reached, when approaching cloud base altitude, or if desired to continue on course or return to the airport. Maintaining orientation while circling is key; the pilot can select the next destination while climbing rather than descending: finding the next thermal, continuing on course, etc. The pilot must ensure the area is clear, roll out on the desired heading, and resume the appropriate speed (L/Dmax corrected for winds and sink). ## Additional Resources [<iframe width="560" height="315" src="https://www.youtube.com/embed/z4xKYfT6aJA?si=j3qJr5HcrRHtOq51" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe>] [<iframe width="560" height="315" src="https://www.youtube.com/embed/XpF0OW8K8Z8?si=tvoDfTO0j-Trcnpw" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe>] [<iframe width="560" height="315" src="https://www.youtube.com/embed/-gUxytvXu28?si=ge-hwPTJsr60YZUH" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe>]