Soaring Techniques

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Soaring flight, maintaining or gaining altitude rather than slowly gliding downward, is the reason most glider pilots take to the sky. After learning to stay aloft for two or more hours at a time, the urge to set off cross-country often overcomes the soaring pilot. The goal is the same whether on a cross-country or a local flight—to use available updrafts as efficiently as possible. This involves finding and staying within the strongest part of the updraft. This chapter covers the basic soaring techniques.

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In the early 1920s, soaring pilots discovered the ability to remain aloft using updrafts caused by wind deflected by the very hillside from which they had launched. This allowed time aloft to explore the air. Soon afterward, they discovered thermals in the valleys adjacent to the hills. In the 1930s, mountain waves, which were not yet well understood by meteorologists, were discovered, leading pilots to make the first high altitude flights. Thermals are the most commonly used type of lift for soaring flight, since they can occur over flat terrain and in hilly country.

There are two favored theories of thermal characteristics. One is that thermals are continuous updrafts like a plume of smoke from a campfire rising up and sometimes twisting depending on the wind currents. This theory requires the glider pilot to locate the rising thermal current and estimate the amount of slant caused by the winds shifting the rising updraft downwind from the heat source. Just like a campfire, the winds may tend to twist and oscillate around the hotter origin.

The other theory is that thermals can be more like a hot water bubble rising in a pan on a stove. If you can stay in the bubble, you can climb. If you spill out of the bubble, there is no lift even just under where you were climbing because the lift is not a continuous vertical stream. The glider pilot must search for the next rising bubble to obtain lift.

In the practical world, the nature of thermals is probably a blend of these theories. The sun produces heat, and often that heating is unequal on the surface of the earth, so winds occur as natural forces that work to equalize the atmosphere. Some of these winds are vertical currents. We call them updrafts and downdrafts. Updrafts provide lift and downdrafts provide sink. Since the atmosphere always seeks equality, if there is an updraft, there must be a downdraft or drafts close to replace the upward flowing air. The goal of soaring pilots is to maximize time in lifting currents and minimize their time in sinking currents.

The contemporary models and experience seem to support the theory of a central updraft surrounded by compensating downdrafts. The skill involves staying in the lift as long as possible and exiting or passing through the sink as quickly as possible.

As a note, glider pilots refer to rising air as lift. This is not the lift generated by the wings as discussed in Chapter 3, Aerodynamics of Flight. The use of this term may confuse new pilots, but when used in the context of updrafts, the energy in a rising column of air is translated as lift. This chapter refers to lift as the rising air within an updraft and sink as the descending air in downdrafts.

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