Successful thermaling technique requires that the pilot locate a thermal, then continuously center on the best lift. For the inexperienced thermal pilot, centering is accomplished simply by decreasing the bank angle as lift increases and by increasing the bank angle as lift decreases. A constant bank angle is held when the lift is constant all the way around. The experienced thermal pilot visualizes the size, shape and position of the thermal by creating a mental picture of it based on changes in vario readings, pitching and rolling tendencies and accelerations felt at various points along the circular path. While continuously updating this visualized mental map, the pilot makes adjustments to the flight path, seeking out the elusive core. Once mastered, thermaling becomes almost second nature, requiring minimal thought effort from the pilot who is already thinking about where to find the next one.

Introduction:

Watching an expert pilot rocket up in a thermal with the glider almost standing up on a wingtip in a tight circle is truly an amazing sight to behold. To actually be that pilot in a high bank turn, centered directly on the narrow core of a powerful thermal, can be the ultimate human experience. But from a purely practical standpoint, the primary benefit a thermal provides, is altitude, which is the stuff of joy to a glider pilot. And a good thermal can lift a glider many, many thousands of feet, which translates into airtime and, if desired, distance. Thermaling skill is therefore essential for successful cross country flying, which for many pilots is the greatest joy of all. The purpose of this article is to provide simple yet effective beginning thermaling techniques and to share tidbits of more advanced techniques gleaned from years of chasing thermals.

CAUTION: Thermals are turbulent by nature. The stronger and narrower the thermals, the more turbulent the air. Not only are there updrafts in close proximity to downdrafts, there are also rotating vortices which can quickly rotate a glider in pitch, roll or yaw. And all thermal pilots eventually experience "going over the falls" which is the transition you make from lift into sink when exiting a thermal. When this happens, the glider pitches over nose down. Always keep plenty of speed when working very strong thermals because going over the falls in such thermals is aerobatic in nature and the extra speed and associated control can prevent a tumble. Only fly slow in mellow thermals. Actually, the safest place to be within a thermal is banked up and centered on its core. As a side note; many pilots thoroughly enjoy riding the rodeo air around thermals.

Finding a Thermal:

Many books and articles have been written by both sailplane and hang glider pilots on the subject of locating thermals. This article does not attempt to cover this subject in detail. However, a few recommendations can be made. Thermals tend to trigger off of pointy things like the tops of ridges or spines. They tend to gather and flow up the center of bowls facing into the wind. They grow on surfaces that face the sun at a direct angle. Look for areas of discontinuity of surface color or texture, such as a meadow surrounded by trees or the upwind edge of a lake or exposed rock outcroppings. On the other hand, thermals rarely come from shady or wet areas.

Sometimes the location of a thermal is given to you. Another pilot or bird circling up is a dead giveaway of an existing thermal. However, be sure that they are, in fact going up, and not circling in sink. A dust devil is also a sure bet if you can reach it with enough altitude to safely go in. When entering a dust devil, be sure to keep plenty of airspeed and enter it turning in the direction opposite to the rotation of the dust. Also, if you are real high, the dark undersurface of a newly forming cumulus cloud almost guarantees good lift. Usually, the area of good lift beneath the cloud is much smaller than the cloud itself. Be sure that the cloud is the newly forming kind because many of the visible clouds are past maturity and have no lift beneath them.

Even though the pilot has some idea of likely places to look to find thermals, most of the time you never really know for sure. However, one truth has passed the test of time: "Lift is where you find it". Put another way, most of the time thermals are simply stumbled upon. Once a thermal is found, then the thermaling skills are applied and it is "worked".

Working a Thermal:

When a thermal is first encountered, the vario will indicate lift. If the initial lift is strong, the experienced pilot will start turning almost immediately, especially if the thermals on this day are small. When entering the thermal, many times one wing will roll up. Turn towards the rising wing because the center of the thermal is likely in that direction. When high on a good day, you can be more choosey about which thermals you want to work and when you decide to start turning. If you are high, and you just encountered lift, continue to fly straight and watch your vario. Many times, thermals are quite big and as you fly straight, the lift will get stronger and stronger. Once the lift starts decreasing, then start turning and go back to the best part. In any case, once a thermal is found, you should start circling, then start "centering" your circles. The skill of thermal centering separates the pilots on the ground from those up at cloudbase. Its that simple. Centering is the key to thermaling success.

Whenever a glider is turning at a constant bank angle, a downward spiral is scribed through the air, which appears to be a circle to an observer looking down from above. As we all know, every circle has a center. When thermaling, the goal of centering a thermal refers to the shifting the center of the glider's turning circle towards the center of the thermal. But how do you know where the center of the thermal is? The answer is you don't at first, but you can find out using some simple proven techniques.

The first step is to get a picture in your mind of what a typical thermal might look like. Think of a thermal as a donut shaped smoke ring. Imagine a cigarette smoker blowing a smoke ring straight up. Notice how the smoke curls up through the center, outward along the top, down around the outside, and back inward along the bottom. Notice that the whole ring is going up at a constant speed but the center of the ring is going up faster. Now imagine you are in a teeny-tiny little glider circling in the center of the ring. You climb rapidly up through the center of the ring, but when you get to the top of the ring, you notice that the climb rate slows down to the speed of the ring as a whole. Also, at the top of the ring, most of the smoke is moving away from the center towards the outside, where it wants to go back down around the outside again. In other words, it is trying very hard to spit you out! And if you do get spit out, you are quickly in the strong sink along the outside of the ring. On the other hand, if your little glider is near the bottom of the smoke ring, the natural flow will draw you inward towards the center of the ring. Although it is true that no two thermals are exactly alike in the real world, this smoke ring picture is probably close to what real bubble thermals looks like, and can be effectively used for thermal visualization. (Donuts, is there anything they can't do?) In any case, a mental picture of a thermal is very helpful when trying to center in, and hang onto a thermal.

So there you are, you just entered some lift and have started circling. Watch your vario as you go around. Usually the circle has a better side to it having stronger lift. You need to shift or displace the center of your turn in that direction. One good centering technique is to decrease the bank angle as lift increases and to increase the bank angle as lift decreases. This method works very well. If you are diligent and attentive, and keep shifting your circle towards the stronger lift, you will eventually become centered on the thermal. Oh happy days! Note, however, that the nature of the beast is working against you and will try to change your bank angle opposite to what you want. To see this, go back to the smoke ring analogy and note that the lift is the strongest right at the center (the core). Imagine that you are flying across the thermal with the core to your left. As you pass the core, its stronger lift will lift the left wing, banking you to the right, which is the opposite direction to what you want. So typically, when working a thermal properly, you are fighting against it, banking towards the wing that is trying to rise. And if you are on top of the thermal smoke ring, the general flow is trying to blow you away from the center. On a typical good day, thermals will spit you out, but don't give up. If you had been climbing for some time previously, a good portion of the thermal is still below you. Just set up a large circle search pattern and go back and find it, it's still there somewhere.

It has been stated that a thermal, by nature, will tend to spit you out once you are inside. On the flip side, when flying through the sink immediately outside a thermal, it will try to guide you back in. To illustrate this, imagine that you are gliding along, slowly sinking out, in search of a thermal. Then imagine that a thermal exists off to your left. The nature of a thermal is such that the sink surrounding the thermal is strongest close to the thermal and weaker farther away. So as you pass by the thermal, you will experience more sink due to the thermal nearby. And since the sink is even stronger closer to the thermal, the left wing will experience greater sink, causing it to drop. This will bank you to the left which is the direction you need to turn to find the thermal. However, turning into increasing sink goes against a pilot's instinct, but it is what the thermal is telling you to do. (If the thermal is really there!)

In order to consistently climb out all the way in a thermal, the pilot must stay focused on continuously staying centered. This is very important and is worth repeating: You must constantly, continuously, unwaveringly and perpetually monitor where the thermal is or you will lose it. And it is very easy to get distracted from the job at hand. Two-way radio communication is a prime culprit. Getting tense worrying about something is another. Fiddling with some piece of equipment is another. Just stay cool, relax, and enjoy the ride! Use your imagination to visualize a picture of the layout of the thermal. And as new data comes in from your vario as you circle, update the picture in your mind so that it reflects reality. Feel when the thermal is trying to bank you one way or the other and sense the immediate accelerations felt when going into stronger lift or sink. By painting and repainting this thermal picture in your mind's eye, you become more aware of the true nature of the thermal. As the truth of the thermal presents itself to you, new, more direct centering methods show themselves. And practice being patient. Some of the best pilots will hang on tenuously to zero sink for hours and stay up when everyone else is going down. After all, you don't fly far when you are on the ground. Once you do get quite a bit of experience, centering in a thermal becomes almost second nature and requires little brain power from the pilot. And your tolerance for thermal turbulence increases. Once this level of skill is reached, then the pilot starts learning new skills. How to not only go real far, but how to get there real fast. Knowing which thermals to pass up and when to exit. Those skills are beyond the scope of this article and the skills of this author.

Safety Nuggets:

Flying in thermals requires launching and landing on days which produce thermals. Duh! For timing your launch on a thermally day, many would recommend waiting for a "cycle" to launch into, to improve your odds of getting up. This seems to be a standard protocol and is perfectly ok on weak days where the thermals are tame and the winds light. However, when flying the big air days (e.g. high desert/mountain sites in mid-summer, or just about anywhere immediately after the passage of a strong cold front), it is this author's strong opinion that one should definitely not launch into a "cycle" in an attempt to get up right at launch. The turbulence during the passage of a "large dust devil" catagory thermal, is extreme, and adds unacceptable risk to the pilot during the critical launch phase, when the pilot is close to the ground. It seems safer and smarter to wait and launch during safe, launchable conditions, where the the wind speed and direction are reasonable and stay relatively constant. These optimum conditions can frequently occur past the middle and towards the end of a large cycle on the light wind days, or during the lull between cycles on strong wind days. Once launched, simply go find one of the abundant thermals and speck.

Landing in the desert during the heat of the day also presents a significant risk. You surely don't want to fly into a dust devil on your final approach (and 9 out of 10 of them are probably invisible). The simplest solution to this problem is prevention: Don't land in the desert in the heat of the day. Stay up until evening when the thermals and winds tend to mellow out significantly. However, if you must land during the kick butt thermal hours, here is a safety tip I always use and highly recomend: first arrive over the LZ with excess altitude, and then hang out upwind of the LZ while losing altitude. If a thermal is out there marching towards the LZ, you will encounter it while you are still high enough to make other plans. One option is to get in the thermal and climb out. Another option is to fly away from the thermal and land out of its reach. (And immediately unhook!)