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Thermals drift with the wind on blue days as well, and similar techniques are required to locate thermals using airborne or ground-based markers. For instance, if heading toward a circling glider but at a thousand feet lower, estimate how much the thermal is tilted in the wind and head for the most likely spot upwind of the circling glider. [Figure 10-5] When in need of a thermal, pilots might consider searching on a line upwind or downwind once abeam the circling glider. This may or may not work; if the thermal is a bubble rather than a column, the pilot may be below the bubble. It is easy to waste height while searching in sink near one spot, rather than leaving and searching for a new thermal. Remember that a house thermal will probably be downwind of its typical spot on a windy day. Only practice and experience enable glider pilots to consistently find good thermals. 

Cool, stable air can also drift with the wind. Avoid areas downwind of known stable air, such as large lakes or large irrigated regions. On a day with Cu, stable areas can be indicated by a big blue hole in an otherwise Cu-filled sky. If the area is broad enough, a detour upwind of the stabilizing feature might be in order. [Figure 10-6] 

## The Big Picture 

When the sky is full of Cu, occasional gliders are marking thermals, and dust devils move across the landscape, the sky becomes glider pilot heaven. If gliding in the upper part of the height band, it is best to focus on the Cu, and make choices based on the best clouds. Sometimes lower altitudes cause glider pilots to go out of synch with the cloud. In that circumstance, use the Cu to find areas that appear generally active, but then start focusing more on ground-based indicators, like dust devils, a hillside with sunshine on it, 

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or a circling bird. When down low, accept weaker climbs. Often the thermal cycles again, and hard work is rewarded. 

When searching for lift, use the best speed to fly, that is, best L/D speed plus corrections for sink and any wind. This technique allows glider pilots to cover the most ground with the available altitude. See Chapter 3, Aerodynamics of Flight, to review shifting of the polar for winds and sink. 

## Entering a Thermal 

Once a thermal has been located, enter it so you do not lose it right away. The first indicator of a nearby thermal is often, oddly enough, increased sink. Next, a positive G-force is felt, which may be subtle or obvious, depending on the thermal strength. The “seat-of-the-pants” indication of lift is the quickest, and is far faster than any variometer, which has a small lag. Speed should have been increased in the sink adjacent to the thermal; as the positive G-force increases, reduce speed to between L/D and minimum sink. Note the trend of the variometer needle (should be an upswing) or the 

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