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Thermalling

Those elusive magical bubbles of lift! They slip through your gliders lines like hot sand through big fingers. They vanish in a puff of warm air. But sometimes they can be the greatest friends, lifting you to cloudbase without a wobble or a tuck. Here's some guidance on catching the invisible collumn to the cumulus. Please note that this advice is based on experience in the Cape Province, South Africa, and may be inappropriate to apply in full to other areas. We experience typical desert flying conditions, unlike conditions experienced in the Alps or in wetter climes.

2.1 How tight to turn?
Now that you're using your averager function of the variometer, you can use it to determine the best turning circle in a thermal. Let's say you're going up at 1m/s. You lean over more, and tighten up the turn, trying to stay in the core of the thermal. Your vario averager now reads 1.6m/s. You widen your turn and allow your wing to fly more level, using 1/4 brakes on both sides. Now your vario reads 0.8m/s. This is a hard-core thermal, and needs to be turned tightly to get the best climb rate. If its a soft-core thermal, you'll achieve a better climb rate with the wide, gentle turn. The secret is to maximise your averager, all the time.

2.2 Exploring in loops
Once you're established in the thermal, and you're confident of where you are, it's good to explore a little to see what's going on around you. Every tenth circle or so, straighten up a bit and make a brief foray beyond your core. You are still turning the same way as always, just widening the circle to include more of the thermal for one turn. This allows you to hook into stronger cores as they come through in the same thermal, and to track cores which shift a lot.

2.3 What if I want to turn the other way?
It very seldom helps to reverse an established turn in an established thermal, because the figure-of-eight path you scribe can lead you out of the thermal completely. But it sometimes pays dividends. I usually reverse the turn direction when I just can't seem to turn tight enough - when the thermal fights my turn more than normal, and something feels wrong. I believe this feeling has something to do with the rotation of the thermal, a phenomenon which is usually unnoticeable. But on some days the thermals tend to rotate, like weak whirlwinds. If you are trying to turn in the same direction as the thermal's rotation, you have a higher momentum and tend to be thrown out by centrifugal force more. This in turn means you have to bank harder to stay in the thermal core. By reversing the turn, you enter the thermal against its rotation, and you are slowed relative to the ground. You have less momentum, and your turn is easier, requiring less bank to remain in the core.

2.4 Doodling around
Once you've been flying for some time, you may want to change from the 'continuous, uniform circling' style, to the 'doodling' style of the highly intuitive pilot on marginal or scrappy days. It works on days when the thermals have multiple cores. It is risky, for a wrong call can result in losing the thermal completely, with far more sink than the lift gained by experimenting. But you'll see a couple of pilots who seem to outclimb everyone, even though they wander about erratically in the thermal, changing direction often. They are responding to small changes in the lift around them, and seeking out the strongest lift in every turn, sometimes linking two or more cores in a wandering doodle. It's hard to do, and even harder to do consistently. It only adds a few percent to your climb rate, and causes unnacceptable traffic problems in crowded thermals (a tactic used by some top competition pilots to outclimb the unsettled 'others'). Please don't try this when there are other pilots nearby. The rule is to all circle the way the first pilot circles in a thermal. If you're on your own, and just not getting anywhere with continuous, uniform circles, give it a try.

2.5 Microlift streams
Small streams of lift exist in the air, wandering around without any more direction than drops of water on a car's windscreen. They are usually too thin to circle in, they offer just a few blips on the vario, but following the stream can result in a dramatic improvement in glide angle, especially into wind. They seem to be more prevalent close to the ground that high up. Expect the stream to wander, and be ready to turn as much as 45degrees off course to follow a turn in the stream. Whichever wing is being lifted, is the way to turn. These streams can often lead you right into your next thermal.

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