Articles
Secrets of Thermal
Soaring
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Winning an RC thermal contest depends on two things, catching the thermal and making a controlled landing. Before we get into any discussion of thermals I would just like to point out that there are no secrets. When I decided to participate in RC gliding on a competitive level I had no idea what was happening out there in the invisible playing field but as time passed I took part in more and more contests, read more articles, spoke to more of the gurus and flew hand launch gliders (now discus launch) I picked up a wider knowledge base of what was happening and learnt to make better (but not always correct) decisions. Above all else don’t be afraid of trying things out, if you think a thermal is on the left then go there, if it wasn’t there then ask yourself why. Don’t be afraid of making mistakes!
What I have found to be the most important concept is not to look at any single indicator in isolation, you have to look at the combination of conditions and indicators and develop an overall picture. We have often gone to the field on days when many of the club pilots say “it is un-flyable”, “conditions are terrible”, “the wind is too strong”, “you don’t get thermals in conditions like this” and had a great days flying. Weather only affects the thermals, it seldom kills them all together and the worst days for me to find thermals are those perfect summer days when the wind doesn’t blow.
Useful tools for finding the elusive thermal
Wind vectors
I have always wondered if there are any teams with mini weather stations or a dedicated person tracking the wind. We first started looking at wind vectors when Chris Adrian brought an article to the field for discussion as part of our preparation for the Turkey (1997) world championships. Rodney (my dad) had insisted that we do information sharing as an effort to improve the team’s general knowledge. Wind vectors are based on the concept that the wind will change from the prevailing wind direction due to modification caused by passing thermals.If a thermal is passing directly overhead then when the thermal is upwind the wind strength will decrease and when the thermal is off to a side then the wind will swing to the side that the thermal is on. The reason that it is referred to as wind vectors is that the change away from the prevailing direction and strength depends on the distance away and strength of the influencing thermal.
So if the change is a little stronger wind and off to the left this could mean that the thermal is either small and to the left or larger and further away to the left. Either way I fly left and downwind. As time passes you will normally feel further change and as the change is a function of time you (if you had a computer built into you sunglasses, like the Terminator) can calculate the exact location of the thermal and its strength. I’m not as good as Arnie so I rely on experience to give me a good idea of where it is and how strong. Either way, this method of finding thermals works well. Especially if the thermal is downwind. This is probably the single reason I go for more thermals downwind than I used to and one of the best methods of finding thermals as it incorporates a thorough understanding and use of the others.The River of Air
A concept in the Old Buzzard’s Soaring Book (an excellent read if you want good thermal tuition) “the river of air” speaks of air as a river with thermal generators being similar to rocks or disturbances in the flow of the river. They are there in the flow and they continue to work throughout the day. A major difference between the river and disturbances and the air and thermals is that the conditions in the river of air continue to change as the day progresses with thermals getting stronger up to a point and then as the day light runs out so the thermals grow weaker. Also the direction of the sunlight against the earth changes and what was a generator early on may not be later on. What is good to note is that if there were two consecutive days with exactly the same conditions then the pattern of thermals would be exactly the same. You must have heard of a home field advantage, well this is where it kicks in, it is better for you to have flown at the field before as you will have created a database of the thermal generators (places where you often pick up thermals when the air is like this or like that). At world championships we try to get as much experience at the field before the actual event as possible. Flying in the pre competitions helps increase the knowledge. We even try and stop at the field when we arrive in the town for the first time so that we can watch where the guys are flying and see as much as possible. Data – this is part of the river of air concept. The other concept is the movement of thermals.Other Planes in the sky
Watch for some basic things during the flight. If you are flying in conditions where there are thermals then pay attention to the launch heights of the pilots that are matched. If a series or grouping of pilots launch higher on one side of the field that the other then there is a thermal in their launching area. Often the pilots launching through the good air won’t follow it so don’t wait for them to realize that it was there. It can’t hurt to fly through this air if you didn’t have anywhere else to go. The usual watching of pilots (this is a job that your caller should be doing not you) is imperative. A good caller will give you an indication of what is happening with the other pilots’ planes and as a good pilot you should be creating an image of what the thermal activity looks like so that if you get into trouble you may be able to save yourself or so that you can mentally compare if it would be better to move to a different area.Upstream indicators
There are often indicators at the field that show where the thermals are, look for wind changes in the trees, the tilt of the trees, smoke from a veld fire, grass moving, flags and streamer or anything else that can show wind direction or strength. As much as I hate to use them as an indicator I am putting this in for Joe Coetzer as one of my best flights at the world championships was from watching the birds (Use this indicator with caution though as birds lie). Don’t forget to use an indicator that is very close to you, your aerial streamer
shows the position of the thermal relative to where you are standing.Downstream indicators are as important
Time the thermal cycle
What are some of the myths
when the air is cold it does not mean there is “bad air” or sink, it often happens because there is a cloud in the way of the sun and the temperature in your vicinity simple drops. The reason it does often indicate sink in the launch area is the other reason for feeling a temperature drop which is because the wind picks up when a thermal has passed to the downwind position and it would be a good idea to launch and chase the thermal downwind. The opposite is also true, when the air feels warm there is not necessarily a thermal – it must be looked at in context.
when it is overcast it doesn’t means that there are no thermals.To win a contest you have to be paying attention to what is happening at the field from the moment you arrive. Track the prevailing (average) windspeed, the spacing between thermals, what happened on the flights preceding yours, what the trend is, the approach of any ominous weather pattern (storm clouds).
F3B contests
F3B contests are slightly different to pure thermal contests as they have speed and distance as additional tasks which have very specific thermal spotting differences.
Distance
In distance you need to try and ensure that you maximize the time of flight in the course in a thermal. If thermals are moving through quickly then you can’t make any additional height gain after launch if a nearby thermal is already passed base B. If the thermal is far (200 + meters) in front of Base B then it is good to launch, zoom forward a bit and thermal in the good air until the thermal reaches a point where the time in course will be maximized. Another thing to remember is that if the thermal will be out of the course before the 4 minutes of available time is up then it is better to maximize laps during the thermal cycle as you lose a lot of laps by flying slowly in the thermal only to have a lot of height in bad air after it is out of the course. The knowledge of what the typical cycle looks like on the day helps a lot here.Speed
You have 4 minutes, don’t be afraid to use them, my team mates hate me in speed as I seldom go with the first launch (this should tell you something (bad) about my local air reading abilities). It is important to have three launches available. If you are a really good air reader then you probably only need one but I am not that good so I will often guess the time of a first launch. If I get it right then great but if I see that line tension wasn’t optimal I will zoom forward and to the side I think the thermal is on. But doing this I can then locate the good air, determine if I must wait for an optimized launch or for better air on course etc. Once the positioning of the good air is definite and knowing what the general conditions are you have to prepare for relaunch, QUICKLY. There is no reason to loiter in the sky or do long approaches. This wastes the thermal knowledge, or makes you miss it if it was very close the first time up. The worst thing to do is take a mediocre set of conditions if you feel it is improving, you only do this when you know it is getting worse.
I hope this has been of some help to you, there are many finer details and many more points that could be discussed - I certainly don’t know them all but if you have questions and I can help then I will. If you would like more help in RC gliding contact me through the contact form (left navigation bar), Marking it for Craig's attention.