17
its strength diminishes. Eventually the thermal stops rising
and any moisture contained in the once warm air condenses,
forming puffy cumulus clouds. These clouds, which mark the
tops of thermals, are usually between 2000' and 5000' high.
THERMAL SOARING
It takes a lot of concentration to thermal soar effectively. A
sailplane can fl y along the edge of a thermal and unless the
pilot is carefully watching the model he may not realize the
opportunity to gain some altitude. Because most thermals
are relatively small, a couple hundred feet [60m] or less at
400' [121.9 m] altitude) compared to the rest of the sky, the
sailplane will rarely fl y directly into the thermal and start rising.
Generally, the sailplane will fl y into the edge or near a thermal
and the effects the thermal has on the plane may be almost
unnoticeable. As the sailplane approaches a thermal, the
wing tip that reaches the rising air fi rst will be lifted before the
opposite wing tip. This causes the sailplane to “bank” and turn
away from where we would like the sailplane to go.
When you are thermal soaring, try to fl y as smooth and straight
as possible. Trim the sailplane to fl y in a straight line and only
touch the controls when you have to. Watch the sailplane
carefully and it will tell you what it is encountering.
When the sailplane fl ies directly into a thermal it will either start
rising or stop sinking. Either case is reason enough to start
circling, especially in a contest where every second counts.
Fly straight ahead until you feel like you are in the strongest
lift, fl y a couple of seconds farther, so that your circle will
be centered in the strongest lift, and then start circling in a
fairly tight but smooth turn. When the sailplane is low the turns
have to be tighter to stay in the strongest lift. As the plane
gains altitude, the turns can be larger and fl atter. The fl atter
the turn, the more effi cient the plane is fl ying. If you see the
sailplane falling off on one side of the circle, move your circle
over into the stronger lift. Thermals move along with the wind
so as you circle you will be swept along with it. Be careful
when thermaling, that you don’t get so far downwind you can’t
make it back to the fi eld to land.
If the sailplane is fl ying along straight and all of a sudden turns,
let the plane continue to bank. You may have to add some
rudder to keep it banked. Continue turning until the sailplane
has completed a 270 degree turn, ¾ of a circle. Straighten
out the bank and fl y into whatever turned the plane. If you
encounter lift, and you won’t every time, start circling just as
you did when fl ying directly into a thermal.
Thermals are generated all day long, but the strongest thermals
are produced when the sun is directly overhead. Some of
these thermals can be very large and you may fi nd it hard
to get out of them. If you fi nd your sailplane getting too high,
don’t dive the plane to get out of the lift. Sailplanes are very
effi cient aircraft and they will build up a lot of speed and could
come apart in the rough air of a thermal. The easiest way to
lose altitude is to apply full rudder and full up elevator. This
will put the sailplane into a tight spin that will not over stress
the airframe but it will enable it to lose altitude very quickly.
This is especially helpful if the sailplane gets sucked into a
cloud or it gets too high to see. The twirling action will give the
sun a better chance of fl ashing off of the wing and catching
your attention.
In a gentle thermal, when you are high enough and want to
leave the thermal, add a little down trim to pick up speed and
fl y 90 degrees to the direction of the wind. If you are not real
high and want to fi nd another thermal, you may want to look
upwind of the last thermal. The same source that generated
the fi rst thermal is probably producing another. Just watch out
for “sink” which is often found behind and between thermals.
As you might expect, with all this air rising, there is also air
sinking. This air is the sailplane pilot’s nightmare that can
really make soaring challenging. Sinking air is usually not as
strong as the thermal in the same area, but can be very strong.
Down drafts of many hundreds of feet (meters) per minute
are common on a good soaring day. These down drafts can
make a sailplane look like it is falling out of the air. Because
of this, it is important that you do not let the sailplane get too
far downwind.
When encountering sink, immediately turn and fl y 90 degrees
to the direction of the wind. Apply a little “down elevator” and
pick up some speed to get out of the sink as fast as possible.
Every second you stay in the sink is precious altitude lost.
POINTERS FOR CONTEST FLYING
Pay Attention: Pay close attention to the sailplanes fl ying
before you. Watch them and try to establish where and when
the thermals are being formed. The thermals are often formed
in cycles and are fairly regular, so if you keep track of the
time intervals you will have a good idea of when and where
a thermal may be generated.
Watch The Birds: Thermals suck up small insects that many
birds love to eat. A bunch of swallows fl ying around in one
area may indicate a thermal. Soaring birds such as hawks,
vultures and eagles are the best thermal indicators. They not
only show you where the thermal is but they also show you
where the center is. These “Masters of the sky” will often fl y
right along with the sailplanes.
Practice Those Landings: Most thermal contests are won or
lost during the landing. Establish a particular landing pattern
and try to stick to it for all landings. Learn to shift your pattern
to account for the wind and particular fl ying fi eld characteristics.
Concentrate: Keep your eye on your sailplane during your
contest fl ights. Have a helper or your counter watch the other
sailplanes in the air. Sometimes your sailplane will wiggle so
quickly or gently that you may miss it if you are not paying
