18
THERMAL SOARING
It takes a lot of concentration to thermal soar effectively. A
sailplane can fly 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 fly directly into the thermal and start
rising. Generally, the sailplane will fly 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 first 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 fly as smooth and
straight as possible. Trim the sailplane to fly 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 flies 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,
fly 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 flatter.
The flatter the turn, the more efficient the plane is flying. 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 field to land.
If the sailplane is flying 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 fly into whatever turned the
plane. If you encounter lift, and you won’t every time, start
circling just as you did when flying 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 find
it hard to get out of them. If you find your sailplane getting too
high, don’t dive the plane to get out of the lift. Sailplanes are
very efficient 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 flashing 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 fly 90 degrees to the direction of the wind. If you are not
real high and want to find another thermal, you may want
to look upwind of the last thermal. The same source that
generated the first 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 fly 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 flying
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 flying 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 fly
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 fly field
characteristics.
Concentrate: Keep your eye on your sailplane during your
contest flights. 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
close attention. If you find a productive thermal, don’t leave it
because your helper tells you that someone else has found
a different one.
