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Old Oct 16, 2012, 11:55 AM
aeajr is offline
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LI, New York, USA
Joined Mar 2003
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Originally Posted by kenh3497 View Post
I just purchased a DLG and am looking for some incite on thermaling.
Learning to Thermal
by Ed Anderson
aeajr on the forums

A thermal is a column of warm rising air that occurs when one section of the
ground warms faster then other sections. As the air raises it draws in
more air. Think of a very slow moving tornado.

Not exactly correct but close enough for first approximation.

Here is a great video on thermals. I highly recommend it!

The Secrets of Thermal Soaring

Almost any plane can thermal, but the lighter the wing loading the better.
Under 12 ounces/sq ft is really good and under 8 is great for gliders 2M and
larger. For DLGs you want to be under 5 ounces!

Many small electric planes have wing loadings in this area so they often
thermal well too. My first thermal experience was with a small electric airplane
called an Aerobird.

Flat bottom or under cambered wings tend to do better than symmetrical or
semi-symmetrical wings but if the lift is strong, you can thermal anything.
In fact we sometimes have to pull out of thermals because the lift is so
strong that the plane can be pulled into the sky and out of sight. I have
seen it happen.

For some people this may sound boring, but I relate it to fishing. You may
cast out many times with no bites. Still, the process is relaxing and

Finally you get a strike and the fight begins.

You go on each fishing trip looking forward to the catch, but knowing that
you will enjoy the process even if you come home with nothing. To
non-fishermen this sounds odd. They just don't understand. Likewise with


The best conditions are calm air, hot sun and low humidity. Some big dark
areas surrounded by lighter areas will help to create thermals, so look to
see if there is anything like that on or around your field. A freshly
plowed field is good. A parking lot works great! A large building with a
black roof is awesome.

However I have caught thermals at 35 degrees F in 15 mph winds. They can be
weak and they move fast, but the are there!

Here are some thoughts on the hunt!

Get your plane up high, the higher the better. Get it well up wind from you
as we are going to glide and drift with the river of air.

If you have a motor, cut the motor and trim the plane for nice level flight.
Now, focus on watching the plane and keeping it on a nice steady glide.
Steady as she goes. Try to keep your hands off the sticks as much as

Let the plane ride with and across the river of air, giving it only
occasional input to keep it going in the general direction you want to go,
but don't be a stickler about it. Let it drift like a fly on the surface of
the river, waiting for a trout.

If you listen with your eyes, it will speak to you, but you have to listen

Glide across the air flow, not into it and not with it. Sort of a 45 -60 degree
left for a while then a 45 to 60 degrees to the right. Nice and slow and
easy. You want to cover the sky and search the moving river of air, like a
bird looking for food.

As you are flying watch the wing tips the nose and the tail. If a wing
seems to bump up, or if the plane seems to become buoyant, floating up for a
moment, it could be a gust, or you might have just brushed a thermal. Go
immediately into a slow turn in the direction of the wing that rose. If
you think you went right through it, fly on for a moment then turn to
circle back into it. It will be moving toward you.

Try to make a circle, but not too tight or you will lose too much altitude.
For 2 Meter and above, try for about a 75-100 foot diameter at first. Under
2 meter cut that in half. Complete a couple of turns
and see if the plane seems to be rising. If it is, just stay with the turn.
We don't want to scare the thermal, we want to bond with it.

Try to observe if the plane is rising steadily, or if it seems to rise and
fall that means you are not centered in the thermal, so work your way more
toward the side of the circle where the plane rises.

Remember that thermals move with the wind, so you are not trying to stay in
one place in relation to the ground. The air is like a river and you are
trying to stay in a little whirlpool that is moving with the river.

If you go into the turn and make a couple of turns with no success, then
just resume the search pattern I mentioned. Angles across the wind. Not
into it and now with it. If you have no success then try a different part of the
sky on the next launch. This is like fishing. You have to cast about till you find
where the fish are hanging out. Typically you will find a region on your field were
the thermals are hanging out, that day. Other days they may be somewhere
else. That is why it is a hunters game. You have to go looking for your prey.

A sailplane in lift

If you are getting out too far, work your way back the same
way, angles to the wind.

Unless you hit a boomer, you are not going to immediately know you are in
lift, so you have to watch the plane. Sometimes it becomes apparent because
you realize that you’re not sinking but appear to be holding altitude. The
only way to do that is to be in lift.

Remember also that thermals can vary in size and intensity. Some are fairly
narrow and some are so large that it seems a whole region of the sky is in
lift. I rode one area recently for 45 minutes where it seemed about 1/4 of
the field was in lift. You didn't really have to circle. You could just fly
back and forth and the plane would rise beautifully. Those are really nice,
when you find them.

It is a hunter's game, if you are up for it.

Good luck pilot! May your hunt go well!


What do Thermals Look Like

Finding Elusive Thermals

Thermals: Collectors, Wicks and Triggers
By Will Gadd

Thermaling on a windy day

Aviation Weather
From the full text of the classic FAA guide

Search Patterns

If you are a new glider pilot, this is a great resource:

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Last edited by aeajr; Oct 17, 2012 at 07:55 AM. Reason: fixed some typos
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