First lets talk about safety. You can screw up big time at 4,000 feet above the ground and still recover without having to change your shorts. Unfortunately, that's not where most of us learn to use thermals. We learn close to the ground, where mistakes must be avoided or corrected quickly.
Thermals that are blown against the ridges tend to flatten out. This makes them difficult to turn 360's in. It does make them easy to do S-Turns or Figure-8's in. That's good news, because it is much safer to do S-Turns and Figure-8's close to the ridge than 360's. Aside from encountering a collapse at low altitude, the most dangerous situation is finding you going downwind into the ridge. When doing maneuvers like S-Turns and Figure-8's this event is less likely to occur. The best way to utilize thermals close to the ridge is to do S-Turns and Figure-8's in the thermal until you reach an altitude where you can safely begin doing 360's. Try to stay in the windward part of the thermal. The boundary layer at the windward side of the thermal tends to be less turbulent than the downwind side of the thermal. Once again this reduces the chance of collapse and keeps you farther away from the ridge.
How high above the ridge is safe? Again, there are many things to consider. Thermals are masses of less-dense air that attempts to accelerate in the opposite direction of gravity. (Straight Up) The faster the thermal accelerates upward, the more force it has. The more force it has, the less it deviates from its path when wind hits it. This means that thermals do not usually drift along at the same speed as the prevailing wind. Stronger thermals ten to be more perpendicular while weak thermals are easily blown with the wind. This means that if you are in a weak thermal close to the ground or a ridge, and there is wind, you must be careful not to be blown back to where you can't penetrate back to the face of the ridge. The danger in this is being blown back into rotor.
If we had entered the thermal from the left we probably would have had fewer problems. The right side of the canopy may start to depressurize, while you are initiating your first turn. But you are weight shifting to the left and applying left brake, which is turning you 90 degrees into the thermal. This maneuver in itself will usually re-inflate the collapsed portion of the canopy. But if it doesn't we are still weight shifting and steering ready to pump out the collapsed wing.
The same thing applies to deciding if you should try to take a thermal close to the ground. If you are within glide range of your landing area, and you encounter a weak thermal in windy conditions, you must be careful when deciding if you should take it. If taking the thermal will cause you to drift down wind at an angle, which will not allow you to glide back to your landing area, you will need to have an alternative LZ somewhere downwind.
As mentioned earlier counting off the seconds after you enter a thermal is a good idea. This will give you an idea of how wide the thermal is, and if it is wide enough to turn in. Depending upon your flying speed, glider's turning ability, and your own experience, you will have your own minimum acceptable second count. Five seconds is a good place to start. After you have counted off the five seconds; turn in the direction where you felt the strongest lift. Use your vario to tell you where the strongest lift is. This is the core of the thermal and the place you want to be in.
As the thermal travels upward, the wind will have different effects on it. It may bend and distort the ideal cylindrical shape of the
thermal. Sometimes thermals are torn apart, creating branches, bubbles, and multiple cores. Each thermal is unique and you will have to form a mental picture of it if you are to use it safely and efficiently.
Just as paragliding brought you into a new world, thermal flying will expand that new world. Bet you can't wait to have your toes 10,000ft. above the ground, wondering which way to start on your first cross-country excursion.
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