This is the first in about three articles I thought I would write about thermal duration flying of R/C sailplanes. In these articles I will attempt to relay what I have learned over the years about thermal soaring. Although I am not a world-renowned expert on the subject of thermal flying, I feel that what I have learned about this subject would be very helpful to anyone wishing to improve their skills. Additionally, it might also stir up more discussion concerning the subject amongst our club members and help to transfer more knowledge about thermal duration flying. So, let's start by discussing what to look for before your sailplane even leaves the ground or your hand.
Those beautiful, puffy, white clouds known as cumulus can be a very good initial indicator of lift. In order for that cloud to form, air hotter than the surrounding air has to rise until the moisture in that air condenses. That means that every cumulus cloud started from rising pockets of air, that elusive thermal! It is possible to find lift under or in the area under that cloud. Have you ever been standing at the flying field and suddenly the air turned very still and much warmer than just a few seconds before? Well, at that time you were most likely standing in a thermal. When you felt the wind again it probably felt much cooler, or maybe even changed directions as the thermal moved on with the prevailing wind of that time.
Wind shifts in direction can also be an indicator of where a thermal may be located. One analogy I have read of a thermal is that it is a large vacuum cleaner, sucking air into it from all around the area. This causes the wind to be drawn toward the thermal and it is particularly distinct on those days when the wind is less than ten mph. For instance if the wind has been out of the south for a period of time and then suddenly shifts to the southwest, it is possible that a thermal could be east of where you are standing. Sometimes the wind can change 180 degrees toward the thermal, so sometimes it may be smart to launch down wind right into the biggest boomer of the day. It is also possible to see this vacuum cleaner effect in other ways, such as leaves of trees or blades of grass shaking and pieces of trash, if not your buddy's airplane, circling in the air.
These "trash-lifters" are just the baby cousins of another very strong thermal, the dust devil. I can remember once many years ago flying with my buddies out at UTD, we saw a dust devil coming towards us from the comer of the field. I launched my Wanderer 99, an old 2-channel polyhedral design by Mark Smith, and flew straight toward the spinning devil. When the sailplane hit the edge of the devil it was tossed around quite' violently. I managed to get the old Wanderer to start circling in the spinning maelstrom with the other trash and a few minutes later the sailplane was just a speck in the sky. Wow, what a ride that was and it was probably the easiest to find of any thermal I have located.
The masters at finding and flying in thermals are the soaring type birds, vultures and hawks are the most common ones you will see in our area of Texas. Watch for them circling in a slow spiraling pattern, most likely they are in a thermal and it is possible to have your sailplane join them for a while. If they tuck their wings in and start flying in a straight line it could mean they found some dinner or the dreaded sink, down air, has arrived in your location. At that point you will have to choose on your own if you want to stay on the ground or if you are flying leave the same area or not. Some people like to use small birds like martins and swallows as thermal indicators, but I personally do not find them very dependable. Another source of information that mayor may not be dependable is our fellow flyers, it is rumored that some pilots will create a "stick thermal" to sucker an unsuspecting competitor. I know that nobody in our club would commit such a despicable act, now would they? Seriously though look for other sailplanes in a thermal going up, really good lift is quite obvious when you learn to recognize it and it may be possible to join them as well.
I hope that this short article was informative and a benefit to all or even some of you fellow sailplane pilots. Please let me know what you liked or disliked about the article. If you have additional information in the same line of thought, pass it on either give me a call or say something the next time we are out flying. Next month I plan to discuss the subject of how to recognize when your sailplane flies into that elusive thermal. So until next month, I hope you have good luck thermal hunting.
