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One of the most fascinating and interesting segments
of RC flying is Soaring. Finding a thermal and rising
without power to unlimited heights is both exhilarating
and rewarding. Once the Radian is up to altitude, one
will be able to soar for hours relying only on thermal
currents and wind to stay aloft. With the current trend
towards an eco-friendly society, thermal soaring is free
energy and fits well with the environmentally conscious
consumer.
Gliders were actually man’s first step to powered flight.
The Wright brothers used gliders extensively to gather
the much needed flight data that allowed them to
eventually achieve powered flight. In essence, a glider
is defined by the fact it continually descends. NASA
space shuttles are in fact gliders by definition. Many of
the troop carriers in World War II were also classified
as gliders. Often gliders are confused with sailplanes,
yet they have completely different functions. A sailplane
is similar to a glider, however, there is one primary
difference. A sailplane can actually soar—meaning it
can rise above its initial launch height.
In the late 1920s and early ’30s, Germany led the
world with sailplane designs. This was partly due to
restrictions placed on them from World War I, when
they could not produce powered aircraft. Due to this,
some wonderful innovations in sailplane designs were
made, and some argue that it was this period that led
to our current sailplane designs and theories. With
modern sailplane designs, it is not uncommon for full-
size sailplanes to stay aloft for up to 8 hours and cover
1000 miles while averaging over 100 mph. Smaller
model sailplanes can fly for long periods using similar
flight theories that full-size sailplanes use. If you have
never experienced thermal soaring with a sailplane
before, you’re really going to enjoy the Radian’s great
soaring capabilities and experience the wonderful sport
of RC thermal soaring.
What Are Thermals?
The first step to thermal flying is to have a basic
understanding of what thermals are and how they
work. If you have some concept of how a thermal
works it will help you know where to search for them.
A thermal is basically rising air. The temperature of
the ground is not consistent. Different textures, colors
and even weather conditions can cause uneven ground
temperature. The warmer ground temperatures heat
up and form a warm air bubble. At this stage, the
bubble will hug the ground until something breaks the
surface tension to release it, much like a soap bubble
breaking away from the water’s surface. Once tripped,
perhaps by a tree line or building, the thermal bubble
then rises up, continuing to gain energy until it is fully
developed many thousands of feet above. Thermals are
typically stronger later in the day because the ground
has had more time to generate heat. There are still
thermals in the morning and evening, but they behave
differently. Morning thermals are very narrow, meaning
they have a small diameter, and do not typically go
very high (20–400 feet). However, there are many small
thermals in the morning, and it is recommended that
you learn at this time of the day. Morning thermals are
very defined yet are safe, as they typically don’t go too
high and are not as violent as fully developed thermals.
Another benefit is there are many smaller thermals
close together in the morning and this will allow
you to hop from one thermal to another with ease.
Evening thermals are typically large warm air masses,
meandering through the sky. They are usually very
smooth with soft edges. The middle of the day (noon to
4 p.m.) is when the thermals are at their strongest.
The downside is that with every thermal there is also
sink. Sink is the surrounding air that is left by the
thermal leaving the ground. Typically sink is on the
upwind side of the thermal. Sink is created when the
warm air has been displaced; colder descending air will
fill the area when the warm air has receded. Sink is not
necessarily a bad thing—because where there is sink
there is also lift close by. The trick is to find lift before
you have to land.
How to Catch a Thermal
Always have a planned search pattern when looking for
thermals. Even the most seasoned thermal competition
pilot will have a search plan before launching. This is
one of the basics of thermal flying. If you have a plan,
based on good sound thermal logic, chances are you
will more than likely find a thermal.
Thermals don’t typically stay in the same location for
long, so maintaining a consistent pattern is important
to ensure as much ground as possible is covered
before landing. Many people just fly straight upwind.
Working in an “S” pattern will increase the searched
surface. Keep working the Radian upwind to cover a lot
more sky for the same loss of height. Also, be on the
lookout for ground markers. Although thermals cannot
be seen, things that identify them can. Wind direction
and velocity are great thermal indicators. Often the
colder descending air filling in the hole that the thermal
created when it left the ground will be a good indication
as to where thermals may be. If the wind has a distinct
change of direction, there is a good chance of a nearby
thermal. The same would apply if the wind shifted to
blow from the right. There would be a good chance the
thermal would be to the left and slightly behind you.
If you feel the wind strength increase, yet it continues
blowing straight into your face, then the thermal is
directly behind you. Finally, if the wind reduces in
velocity, or even stops from a steady breeze, then
the thermal is either ahead of you or right above you.
Basically the thermal will be in the direction that the
wind is blowing towards. Always pay attention to the
general wind direction and look for changes in both
its direction and velocity as signs for thermals. Other
ground signs are birds. Many birds are capable of
soaring, and you will often see them soaring on the
thermals. Before launching, always check for birds.
Pay close attention to how they are flying or if they are
flapping hard—chances are they are also looking for
lift. If they are soaring without flapping, then there is
a good chance they are in lift. Birds also like to feed
on small insects. As thermals initiate from the ground,
often they will suck up small insects into the air. Birds
will often feed on these insects and indicate another
sign that there is lift. If you see birds flying in circles,
almost in a feeding frenzy, there is a chance that lift
is in their proximity. Another idea that works well is to
fly over areas that are darker. Often a freshly plowed
field, a parking lot, dirt—anything with a dark color will
generate more heat—could also be a good source of
generating thermals. One little test you may like to do is
to paint various colors on a sheet of paper and place it
in the sun. After 30 minutes or so, go and check which
colors have created the most heat. Once you know
what colors make the most heat, look for natural areas
on the ground that match these colors and use those
as locations for thermal hunting.
What to Do When You Find a Thermal
The first thing one needs to be absolutely sure of is that
a lift has truly been found. Often a sailplane may find
what is called a stick thermal, meaning you may have
been carrying some additional speed and the model
will climb by pitching upward. One of the best signals
when the model is truly in lift is it will slightly speed up
and the nose of the aircraft will be down slightly. The
model will feel more agile and responsive. Once lift is
found, start circling in a moderate circle (50–75 foot
radius). Then determine the size of the thermal. If the
Radian drops on one side of the thermal and is more
buoyant on the other as it circles, it has reached the
boundary of the thermal. The parameters of most
thermals are clearly marked by the downward flowing
air. The center has fast rising air and the outside has
downward rolling air (often called the edge of the
thermal or the thermal wall). In the middle of the day
when thermals are at their strongest, the thermal wall
can be very distinct and violent, yet in the morning and
late evening they are much softer. The objective is to
make sure one is completely inside the thermal. This
is called centering or coring the thermal. You will need
to constantly make adjustments to keep in the center
of the thermal. Maintain climb all the way around each
360-degree circle. Often, especially if it is a windy day,
thermals will drift with the wind. Most will travel directly
downwind. One thing to remember is your Radian will
also drift with the wind, especially when circling, so
once the core of the thermal is established, the Radian
will naturally drift with the thermal. One mistake people
make is they don’t allow their model to drift with the
thermal, hence falling out of the front or side of the
thermal as it drifts downwind.
Slope and Alpine Lift
Another form of soaring is slope lift. This lift is caused
by wind rushing over a hill, cliff or any solid land mass
that has more than 30 degrees of slope. As the air hits
the hill or slope, it is redirected in an upward motion,
thus creating lift. The best example of this is hang
gliders that are soaring on the cliff faces. They maintain
flight by soaring on the updrafts created by the sea
breezes hitting the cliffs and creating what is known as
slope lift. This sort of soaring is a lot of fun with your
Radian, as you can always motor back to a safe landing
if the lift falls away. The important thing to understand
with slope-type lift is the wind must be almost directly
blowing up the face of the hill or slope. Any more than
a 20-degree variation may cause more turbulence than
actual lift.
Alpine soaring has been popular in Europe and is also
becoming popular in the US. It is the extreme end of
thermal soaring. As thermals develop deep on the
valley floor, they rise up the mountainside reaching their
climax at the top of the mountain. This is often marked
by a strong breeze blowing at the top of the mountain,
which is in fact a fully developed thermal. One of the
benefits of the Radian is that it has power assistance.
Even though it does have an electric motor that will
allow quite a steep climb, the primary purpose of the
motor is a launch device so if the lift does go away, the
Radian can motor back to a safe landing point.
We hope you enjoy your Radian and, more importantly,
experience the art of thermal soaring. As this may
be your first electric-powered sailplane, we hope this
document has given you the basic ingredients to
enhance your enjoyment with this wonderful product.
We wish you all the best and happy thermal hunting.
Simple Soaring
