How to find those invisible and elusive thermals
One of the most fun aspects of rc airplane flying is finding a thermal and staying in the air for a long flight, while your flying friends are struggling at low altitude or are stuck on the ground.
Talk about bragging rights! Entire contests are built around this simple idea, and the top pilots have legendary status world-wide.
Well, how do find something that's invisible? You look very closely.
Searching for thermals actually begins before you launch the airplane.
-Observe the layout of the field
-Observe what's over the field
-Observe the wind
-Pay attention to the changes in the wind
-Find a thermal in a hurry
First, observe the layout of the field. Do you see dark areas (trees, asphalt) and light areas (dirt, light colored buildings)? These different colored areas tend to absorb heat at different rates, creating thermals.
NOTE: thermals can be created during the winter.
It's the difference between heated areas that matters. The thermals do tend to be stronger in the summer-time.
Now, observe what's over the field.
Do you see hunting birds circling? That's a dead giveaway, but not always present.
How about swarms of bugs? Another sure sign.
Next, observe the wind. Look at any flags, and remembering the wind will push the thermals downwind, so you will need to adjust your circling pattern to stay centered in any thermals.
As be aware of changes in the wind speed and direction.
Check the direction by throwing a flew blades of grass into the air and watching what happens.
Now face into the wind. Say the wind is smoothly from the North at about 8 mph, then suddenly there is no wind for a few seconds, then it starts backs from North at about 8 mph.
What just happened? A thermal just passed over your location, heading South!
Remember that the thermal sucks air into its center; this causes the prevailing (dominant) wind to change for a little while. By paying attention to the changes in the wind, you can get to the point where you launch into a thermal, or very nearly so.
Then turn downwind and keep circling to stay in the thermal. Your skills will also develop to the level where you can sense the changes even while paying attention to your aircraft in the air.
Now assuming you are in the air, and need to find a thermal in a hurry. The airplane is descending as gliders do, but you want to keep flying.
First of all don't panic!
These things are designed as thermal gliders, remember? If it's starts coming down fairly close to the ground, steer it towards you and prepare for landing.
But say you're fairly high up after launch, and they are no birds or obvious wind changes, what now?
Well, you need to fly to areas where you think there might be thermals. Fly to the boundaries of warm/cold areas, eg where dark asphalt meets light baseball field. If the plane starts going up, begin to circle in the thermal.
If not, fly to another area. If you're out of "obvious" thermal generating areas, try flying long paths back and forth across the field.
If you fly through a thermal, the glider will react to it. In general, one wing will suddenly rise without any input to the transmitter, if that happens, turn back and try to circle and center in the thermal.
It's a good idea before you launch to have a "decision height" in mind.
This is the point at which you setup for a landing and bring the plane in, eg: when the glider gets below 50 ft.
As you get more experienced, this height might decrease.
The height will also depend on how far away the thermal glider is from you. For example, you might not worry about 50ft directly overhead, but 50 ft of altitude a half-mile away could be asking for trouble.
The idea is, try to respect your current skill level and limitations, and land a little sooner rather than a little too late..