Basics of Thermal Flying
This article is intended to provide some basic techniques for ascending in thermals. It will also add some discussion of where to look for thermal triggers. The article Flight Plans and Primary Flight Paths should underlay all concepts discussed here. This means that continuing to circle in thermals comes secondary to ensuring you will make it to the LZ safely.
Thermals come in many shapes, sizes and textures. Some thermals are too small to circle in, while others can be so huge that you have to try to find your way out of them. Some are just strong enough to maintain your altitude, while others take you up so fast it can be disconcerting. Active flying is the approach that will help you manage your wing while thermalling, but the following should make climbing in thermals easier.
Where to Find Thermals:
- Over Higher Terrain
- Sunny Side of Ridges and Terrain
- Where Other Pilots And Birds Are Marking The Thermals
- When Low Fly Terrain, When High Fly the Sky
- Always Ask the Locals About Trigger Locations And House Thermals
Thermals form as a result of the ground heating the air. So, thermals always release from the ground. As they rise, thermals usually drift toward mountains or ridges (we are not discussing “flat land thermal flying here”). As they rise, thermals follow the ground upwards toward the higher terrain where we launch from. The thermals then follow and release from the tops of the ridges, spines, or hills. There are occasionally some exceptions to this, but generally the best path from launch to LZ will direct you over ridges and higher points on the route.
A good way to picture where thermal release from is to do the following:
If you picture a 3 dimensional / relief map of the mountain and flipping it upside down and dipping in water, where would the water drip from? The high points on ridges and from the top of the mountain.
A morning flight at a certain site might have a different primary path to the LZ than a flight in the evening at the same site. You have to look at where the sun has been shining and heating for the past hour or more and combine this with wind direction to have a good idea. The best source for briefings on flight path and primary path specifics will usually be the locals and your instructor. Have a flight plan for each flight to know what areas to stay above and what areas to avoid.
When you are on route, if you are flying near another pilot or birds are climbing near you, this is a great marker telling you where to go. Once in a while you will miss such the thermal even with such a marker, but more often than this, you will find a good thermal to go after.
Before flying any thermal site, get a site introduction with specifics of the terrain, location of hazards and where common thermal triggers are. The pilots that fly a site frequently have a giant advantage and know where the most consistent locations for the thermals are. They can also brief you on hazards to avoid and generally make your flights safer and more profitable.
A main saying about thermal flying is this, “When low, fly the terrain, when high, fly the sky”. The reason for this saying is that wind drift and such change where the thermals go to. Since the cumulus clouds are the result of the rising thermals, they are basically markers of where the thermals are when you are up higher. There are not always clouds present when you are flying thermals, but they certainly make it easier when they are there and you are high. Use the clouds to help you find lift and thermals. The water vapor that form the clouds becomes visible after the thermal reaches an elevation where the temperature, altitude and pressure allow this to occur. Clouds can be in the process of building when a thermal or several thermals are feeding the cloud. The opposite dissipation happens when a cloud is not longer being fed and it appears static or slowly reducing in size.
Look for clouds that are in development stages and when not too far from your primary flight path, look under and slightly upwind of them for thermals. This is not always the easiest task, but by being persistent in trying to learn this, you will eventually gain skills in seeing this. When low, it is better to stick with flying the terrain. Down low thermals can come from specific ridges. When you can begin to recognize trigger points that thermals would likely release from (high points on ridges, elbows etc…) you can try to fly above such points to catch that branch of the thermal. Up higher, where the clouds are, the thermals can be a combination of several of thermals like each of these. So, often the thermals that you find lower are smaller and the better way of finding them is to use the terrain.
Learning how to differentiate between building and regressing clouds could be a full article in itself and takes solid experience to have the eyes for. The nice thing here is that when you are high and trying to fly clouds, you normally have some altitude to spare to experiment and fly under clouds to test the air.
In Thermals / Basic Technique:
Once in a thermal, some techniques will help you to climb better. If there are pilots circling above you in it, make sure you circle in the same direction. This is one of the most important right of way rules for thermal flying. Also, ensure that prior to entering and circling in the thermal, that you will have plenty of clearance from terrain and trees should a collapse happen or if you lose the thermal at some point in the turn. Having extra padding in this regard will keep you out of trouble and pad your safety.
As you enter a thermal, it can feel similar to encountering a gust as the paraglider’s leading edge will slow and pitch up. When this first occurs, make sure you let your brakes up to help the glider accelerate and return to a normalized angle of attack. Once the glider has stabilized its pitch, smoothly slow down to minimum sink speed or slightly faster (Never fly slower than Minimum Sink Speed, there is no advantage, you start descending quicker and you start to get closer to a stalled angle of attack). You now need to check to see if the thermal is big enough to circle in. A good way to do this is to count to 3. Begin counting “one one thousand, two one thousand, three one thousand” just after entering the rising air. If the thermal is over 3 seconds in size, it is likely big enough to circle begin circling in.
It is imperative that you make sure you are going up when you begin circling in thermals. Younger / novice pilots sometimes start to go up in a gust of wind and mistake it for a thermal. Then, they begin circling and actually are losing altitude and can compromise their chance of making the LZ. If there are nearby hills or mountains, you can de-reference if you are going up by gauging the ridge tops against the backgrounds. If you are using a variometer, this can help, but it is important to have visual confirmation as well.
For the sake of simplicity, we will assume that no pilots are in the thermal in the following discussion. If pilots are in a thermal, you need to circle in the same direction as the other pilots to obey the right of way rules and avoid collisions.
If the thermal you encounter is centered in front of you, neither more on the left nor the right, choose which way to turn. Begin counting (one one thousand, …) as soon as you start to rise in the thermal. When you have reached “ … three one thousand” you should be flying at or slightly faster than minimum sink. You should also still be ascending. Min sink is the most efficient speed for climbing in thermals or anytime the lift is strong enough that you can maintain altitude or climb. If you have confirmed you are still climbing, start to turn into the thermal by letting the outside hand up and provide strong weight shift. To help the paraglider bank towards lift, weight shift becomes super important to help you get the glider to bank into the thermals. When the thermals are punchy or small, add a little speed to the inside hand. By keeping a bit more speed in the glider, your glider will have a little more energy and the ability to turn better into a thermal that would over-power you otherwise. For medium or larger thermals, using min sink as a base can be fine.
Once you have made a full 360, you can start to picture how big the thermal is and how well centered you are in the thermal. I think of the thermal in my memory and focus on where the lift was greater or lesser. Try setting a bank and after a turn or so, you can begin to see if the bank angle you set fits the thermal. If the thermal is lifting much more in 1/2 of your 360s, you can try to re-center in the direction you picture the lift in. More important though, is to make sure you keep your bank angle steady. If you are constantly changing your bank angle, you will wobble around and inefficient. You will also mistake slight pitch changes for lift and lose your connection to feel and where the thermal truly is.
When in a thermal, you can do your turns by letting up on the outside hand. Since you should be flying minimum sink or slightly faster, turns can be done with lots of weight shift and letting the outside hand up to turn. The inside hand remains static, at minimum sink level or slightly faster and the adjustments to bank and pitch are done with the outside hand. This style of turning helps you improve the sink rate and bank angle and maximize how fast you are climbing.
There is no substitute for practice. If you want to become great at climbing in thermals, you will need to get good at circling in small thermals as well as the fat ones that anyone can climb in. What sets the better pilots apart is that they can climb in light thermals much better than the rest of the flock.
Keeping a steady bank angle while thermalling will help you climb better and smoother. Newer pilot frequently over adjust in their attempts to center and re-center in the thermal. The fluctuations in bank often become similar to PIOing (Pilot Induced Oscillations) in the thermal and this results in inefficiency.
After you have determined how large the thermal is, you should try to set a bank angle that is small enough to keep you inside the perimeters of the thermal, but not so small that you are only circling in the side of a larger thermal. After a 360 or two, you can make some minor adjustments for where you are circling and how much bank angle to continue with.
To keep the bank steady, you need to smoothly and effectively react to changes that effect your bank angle. When lift increases under your inside wing, you will need to add hard weight shift and let the outside hand up more to counteract the wing trying to flatten its bank angle. Or, when the opposite happens, back off a bit on the weight shift and lower the outside hand slightly.
Pitch movements also are involved in keeping the bank angle steady. When the glider has more speed, it will react stronger to a turn input than when its speed is lower. Just as you let the brakes up as you enter a thermal, when the pitch increases and the wing begins slowing, speed up a little as you prepare to adjust the turn.
Hazards to Avoid:
- Circling / Flying Too Close To Terrain
- Circling But Not Ascending (can you make the LZ?)
- Flying Into Mechanical Turbulence (downwind of trees, ridges, peaks)
- Flying Close In Crowded Skies (wait till your experience grows before you begin flying tightly with others)
- Flying At Site Or On Days Too Strong For Your Ability
- Not Preparing Enough (Weather, Hazard Knowledge, Site Info etc.)
More to read up on:
Will Gadd wrote the following 3 part descriptive papers about Thermal flying. These articles go into a bit more depth than the above and are intended to help more advanced pilots reach cross country level flying.
Will holds multiple records for World Paragliding Distance and has more flights over 100 miles than just about any pilot in the world. These articles will help expand on some of the concepts discussed in the above article.: