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## Atypical Thermals 

Exceptions to normal or typical thermals are numerous. For instance, instead of stronger sink at the edge of a thermal, weak lift sometimes continues for a distance after leaving a thermal. Glider pilots should be quick to adapt to whatever the air has to offer at the time. The mechanics of simply flying the glider become second nature with practice, as do thermaling techniques. Expect to land early because anticipated lift was not there on occasion—it is part of the learning curve. 

If thermal waves are suspected, climb in the thermal near cloud base, then head toward the upwind side of the Cu. Often, only very weak lift, barely enough to climb at all, is found in smooth air upwind of the cloud. Once above cloud base and upwind of the Cu, climb rates of a few hundred fpm can be found. Climbs can be made by flying back and forth upwind of an individual Cu, or by flying along cloud streets if they exist. If no clouds are present, but waves are suspected, climb to the top of the thermal and penetrate upwind in search of smooth, weak lift. Without visual clues, thermal waves are more difficult to work. Thermal waves are most often stumbled upon as a pleasant surprise. 

## Ridge/Slope Soaring 

Efficient slope soaring (also called ridge soaring or ridge running) is fairly easy; simply fly in the updraft along the upwind side of the ridge. Although the appearance may seem simple, it is very complicated and can be very hazardous for the untrained glider pilot. Ridge soaring can also be very demanding on the glider and the pilot. Even though it is easy to fly, there are many situations in which a glider pilot can be exposed to hazards if proper training has not been 

received. A thorough preflight and route planning needs to be accomplished. This planning also includes ridge selection based on the current winds. The horizontal distance from the ridge varies with height above the ridge, since the best lift zone, or optimum lift zones (OLZ) tilts upwind with height above the ridge. These zones, or OLZ, vary but usually are slightly off the top of the ridge, with a slight angle into the prevailing wind. The bottom of the OLZ may be slightly down from the top line under normal conditions. These OLZ vary with the size and terrain makeup of the ridge. [Figure 10-14] 

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Surface winds of 15–20 knots that are perpendicular to the ridge are ideal. Wind flow within 45° of the perpendicular line also provides adequate lift. Winds less than 10 knots have also produced adequate ridge soaring dependent on the terrain, but with 10 knots of wind or less, pilots should avoid flying low over any ridge due to the possibility of encountering sink. Local ridge pilots know about of these conditions and the need for good preflight planning and training is required.  [Figure 10-15] 

• Airflow mirrors a hill or ridge shape. Imagine a flow of water around the ridge instead of air. However, air is thinner and can be compressed as in a “venturi effect” and can be “squeezed” and accelerated, especially along the ridge. [Figure 10-16] 

• Ridges that have an irregular profile are hazardous. The more complicated the ridge is, the more erratic the airflow may become. [Figure 10-17] 

## Traps 

Even though the idea is simple, traps exist for both new and expert glider pilots. Obtain instruction when first learning to ridge soar/slope soar. Avoid approaching from the upwind side perpendicularly to the ridge. Instead, approach the ridge 

