AHHHHH...thermals. Lot's of talk about them and lot's of mis-information.
As a LONG time RC Sailplane flyer, and also having a number of hours in Sailplanes in both thermal and ridge lift, maybe I can shed a wee bit of light on the subject.
Thermals are pretty simple critters. They are a column of rising air. This air is rising because it is warmer than the surrounding air. Note that it makes no difference how warm or cold the air is. All that matters is that there is a temperature difference.
Now, I don't have enough experience in FSX to claim to know how thermals are generated in the sim, but I can tell you a bit about the real world.
Thermals come from uneven heating of the earth by the sun. If you've ever walked barefoot in the summer you have felt this first hand when stepping from a grassy area onto a paved area. Now, in time, the air above the paved area will become warmer than the air above the grass. At a certain point (don't ask about HOW much warmer cause I can't tell you that) that air will 'break loose' and start to rise. That air will rise and start cooling off as it rises. Eventually it will be at the same temperature as the surrouding air, and the thermal has 'topped out'. USUALLY, that also results in a cloud as the water vapor in the rising air condenses. Thermals also 'drift' with the wind, and will always be 'down wind' from the point that they were generated from.
When looking for thermals you look for large paved areas, dark areas of land such as freshly plowed fields, any place where there are distinct differences in the color of the terrain. Darker areas will be the 'thermal generators'.
You can visualize a thermal as being almost like an old fashioned ice cream cone. Narrow at the bottom, and getting larger as it rises, with the ice cream/cloud at the top. They will be stronger in the center, and at lower altitudes, you will have to be in a pretty steep bank to stay in one. As you gain altitude, you can flatten out the turn more and stay in lift.
Finding thermals can be difficult at times, but the same areas ALWAYS produce thermals, and around glidere ports, and RC Flying fields we call them 'house thermals'. It's pretty easy to tell when you have found a thermal. A well trimmed sailplane will do one of two things, depending on what part of a thermal you find. If you fly directly into one, the nose will rise, the airspeed will fall off, and the sailplane will want to stall. If this happens, you put a bit of forward presssure on the stick to 'penetrate the thermal', watch your vario, and fly THRU it until you lose the lift and then turn back into it. If you find the edge of a thermal the sailplane will want to turn AWAY from the thermal as the rising air under one wing will make it rise and bank away from the lift. If that happens, you simply turn bank back into the rising wing, and use your vario to 'center the lift' and off you go.
Finding the center of the thermal is the hardest part. You need to use your vario, and vary your bank so that you get (if possible) an equal rate of climb thru the whole circle. Generally, you want to increase your bank as the vario starts to drop off, and lessen it as the vario rises.
That's just a general once-over, but it should be enough info to get you started.
Here are a couple of sites that probably explain it better than I can (plus they have pitcures)
http://www.aerospaceweb.org/question/nature/q0253.shtmlhttp://www.answers.com/topic/gliding this has a lot og good likns in it also
