The Path to Improvement in Thermal Soaring

By Bill Kuhl


After my first year of sailplane flying, I thought I was a fairly competent RC sailplane pilot. The second year of flying, my flying improved significantly also, in fact every year I seem to improve some. This made me realize this is a hobby that will provide continuous challenges. The first couple years, I often blamed the conditions for difficulty in thermaling, as my skills improved I found success staying up in lift in more conditions. With sailplane flying, fishing, and many other things, luck should be a decreasing factor in your success as you improve.

The objective of this article is to discuss attitude and approach to improving thermal flying skills, not so much technical details covered in many other sources. It is about breaking down the elements and practicing smaller parts before trying to perfect everything at once. Hopefully I can offer a couple of tips that have helped me.

In writing this article, I came up with several points that were important to me.


Your success or failure has more to do with controllable factors than by luck, good or bad. Seemingly small factors added together can give big results. The skills will not be learned overnight, if they could be it would not be such a challenging, interesting hobby.

Adjusting Your Attitude

It is only natural to think that the small things really don’t matter, how could a slight difference in the curve of a wing make a difference? In an activity that is so much about efficiency, all the little things together can make a huge difference. One of the biggest attitudes to overcome is that your skills don’t need improvement. Contest flying should prove to you that there is room for improvement.

The fair weather attitude is one I admittedly have problems with, practicing only on days with light wind and plenty of sunshine, will not make you a competent contest pilot. Besides, when you try to fly on the slope in 30 mph winds, it will be a traumatic experience when landing without some windy weather experience.

If you have power plane experience, following thermals will take some change in your flight paths over the field. As Dave Thornburg stated, “thermals don’t care about field boundaries, tree lines, and such. In Thornburg’s video I thought he made it seem like thermals travel in a straight line downwind. Paul Naton in his Secrets of Thermal Flying video showed graphics of how the path of a thermal downwind can take many twists and turns in the path downwind. This appears closer to real world conditions in my opinion.

Practicing the Parts

Selecting, building, and trimming a sailplane has been covered in many articles; what is important, is to have a good flying sailplane. If the sailplane is fighting warps or the center of gravity is incorrect, the performance suffers greatly. A sailplane that thermals easily, will give you more practice.

The areas I practice; revolve around finding the strongest lift and making the most of the lift by smooth flying. Through practice learn to recognize the ground signs, and fly in marginal lift conditions to practice smooth flying.

Practice Recognizing Ground Signs

Many articles have been written about using the shifts in wind and changes in temperature to locate thermals. These are often subtle signs, especially changes in temperature.

With repeated practice over time you become more sensitive to changes in temperature and wind speed and direction. Try to correlate wind dropping, and finding lift directly upwind. Notice when it all of a sudden it gets much warmer right where you are standing.

What makes spotting lift tough, is that while you are trying to figure out where the lift and sink might be, you also have to fly the sailplane. You have to become so comfortable flying the sailplane, that your brain can think about other things.

At first you might want to have devices to help with this, such as thermal flags. Besides a thermal flag, I purchased an accurate wind speed indicator and a heatsensitive thermal indicator like the free flighters use. What I found, was that the temperature changes were pretty small, normally only a few tenths of a degree. Wind speeds changes were more dramatic, often jumping up and down several miles per hour within a short time period. Eventually you get to the point where you feel it is getting warm or you feel the changes in wind speed, or direction on your body.

Recognizing Changes in Speed

Along with ground signs, develop your skills in detecting lift by watching your airplane. Recognize the changes in speed. With hours of practice the little changes in speed were more noticeable to me. Observing the sailplane suddenly pickup speed was a very clear indicator to me that it was in lift. Not as obvious was when the sailplane was slowing down, it was most likely in sink. Recognize when the plane is working hard to penetrate the wind, this is really killing performance. If the plane is inside the thermal it shouldn’t have to work so hard trying to penetrate.

Practicing, Smooth Flying

With a limited amount of energy, not wasting it is very important. You might think your flying is smooth, but practicing flying in margin lift conditions may prove there is room for improvement. Recognize that any control inputs you are using are creating drag. Think about your flying in terms of energy. The plane is flying with only so much kinetic energy; unnecessary movements such as extra control movements, stalling, or sharp turns, will bleed of the kinetic energy very quickly. The smaller the plane, the worse this will be.

Tight thermal circles turns take a huge amount of energy, if the plane is not circling in lift, the potential energy of altitude is being lost. This means it is best to have a high degree of certainty that you are entering lift, if you hit weak lift, adjust quickly to find stronger lift, or straighten out to fly out of sink.

Learning to Fly Smooth – Ways to Practice

Fly in conditions of lighter lift; I often fly later afternoon, early evening. With practice I am climbing in lift later in the day consistently.

Practice flying with an under-powered electric slow-flight plane and try for as long a duration as possible. I noticed that a slow-flight plane of mine would barely climb when other people were flying it (beginners and glow-powered pilots). Most of my flights were of considerably longer duration and of higher altitude because I was using less and smaller control inputs.

Practice flying smooth by flying from small slopes; to stay up on a small slope takes very smooth flying, recognizing when the lift is decreasing or increasing. When the plane is climbing in lift, that is the time to turn. When you are in the core of the thermal, this is when you can experiment with turning tighter to see if the plane goes up even faster. Keep working to have the plane climbing around the entire circle.

Circle in the lightest lift as long as possible. Often with my hand launch I will try to locate lift until I catch the plane, then quickly throw back where lift was spotted and proceed to climb out. When the plane is circling 15 feet high chances of climbing out are not very good, but you can easily see what is going on with your plane.

Location, Location, Location

As important as location is in real estate, so is finding the exact location of the thermal core. If you are not flying in lift, it doesn’t matter how efficient your glider is or how smoothly you are flying. Even though your sailplane is gaining altitude, it might not be in the strongest part of the thermal. The “Secrets of Thermal Soaring” video from Radio Carbon Art diagramed the strength of lift by assigning a numerical values to lift or sink, with sink represented in negative numbers. If your plane is flying in the lower number positive lift, it is very close to the negative number sink. Working toward the strongest lift, increases chances of avoiding sink.

Putting It All Together

I hope these suggestions might help you improve your thermal flying, at least a little. Nothing earth shattering here, but if you work to improve all the small components, it can add up to big results.