E-flite Mystique RES 2.9m ARF - Manual (Page 38)

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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
4:00 p.m.) is when the thermals are at their strongest.
The flip side to this 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
downwind side of the thermal. Sink is created when
warm, rising air is displaced by colder, descending air.
This 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.
Thermals can also start at ground level. And if you are
skillful enough, you can catch a thermal from 20 or so
feet and ride it up to 1000’.
how to catch a thermal
One of the best pieces of advice we could give you is to
always have a planned search pattern when looking for
thermals. Even the most seasoned thermal competition
pilots will have a search plan before launching. This is
one of the basics of thermal flying. If you have a plan
based on sound thermal logic, chances are you will more
than likely find a thermal.
As thermals don’t typically stay in the same location
for long, you can’t just go to the last place you found a
thermal. Often we hear pilots say, “Fly over those trees.
There is always lift there.” In reality, this may have
been a location where they did in fact find a thermal;
however, it may not always be there. Our advice is to
have a planned search pattern, ensuring you cover as
much ground as the model is capable of before landing.
Many people just fly straight upwind. This is ok, yet
we would suggest working in an “S” pattern, which will
increase your search pattern. You can still keep working
your model upwind; however, you are going to cover a
lot more sky for the same loss of height if you work your
model in an “S” type flight pattern. You don’t have to go
out of sight each way either; perhaps 300’ either side
of center will be sufficient. Also, be on the lookout for
ground markers. You can’t see thermals, yet you can
see things that identify them. These are your ground
markers.
Wind direction and velocity are also great thermal
indicators. Often colder, descending air fills in the hole
that a thermal leaves as it moves along the ground.
Traveling downwind of a cooler air mass might be a good
indication of where a thermal may be. If the wind has
been steady in your face and you feel a distinct change
of direction, perhaps shifting more from your left, then
there is a good chance that the thermal is to your right
and slightly behind you. The same would apply if the
wind shifted to blow from the right, as there would be a
good chance that the thermal is to your left and slightly
behind you. If you feel the wind strength increase, yet
stay 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 where the wind is blowing toward. Always
pay attention to the general wind direction and look for
changes in both its direction and velocity for signs of
thermals.
Other good indicators 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. 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, birds will suck up
small insects sent into the air. A circling bird is a great
sign that there is lift.
Another idea that works well is to fly over areas that
are darker, often a freshly ploughed field, a parking lot,
dirt, or anything with a dark color. Since darker colors
absorb more heat, they could 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
them in the sun. After 30 minutes or so, go and check
which colors absorb 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. While these are just a few
helpful search options for you, we are confident that as
your knowledge and understanding of thermals improve,
you will start to have your own special thermal hunting
locations.
what to do when you find a thermal
Probably the first thing you need to be absolutely sure
of is if you are in lift. Often a sailplane may find what we
call a stick thermal. It’s a tongue-in-cheek term meaning
you may have been carrying some additional speed
and the model will climb by pulling elevator. One of the
best signals you will see 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 you have found your lift and you’re sure
it is lift, start circling in a moderate circle, about a 50–
75’ radius. The next thing you need to do to determine
is how big the thermal is. Once circling, you may notice
that your model may drop on one side of the thermal
and be more buoyant on the other. The perimeters of
most thermals are clearly marked by downward flowing
air. If you have seen an atomic bomb cloud, then this is
a good visual for you to understand what a thermal can
look like. The center has fast, rising air and the outside
has downward, rolling air, often known as 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 much softer.
Keeping this in mind, the main objective is to make
sure you are completely inside the thermal. This is
called centering or coring the thermal. You will need to
constantly make adjustments to stay in the center of the
thermal. Keep checking you are getting an even climb
all the way around each circle flown, as you may not be
completely centered in the thermal. 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 model will also drift with the wind, especially when
circling. Thus, once you have established the core of the
thermal, your model will naturally drift with the thermal,
much the same as a free flight model will. One mistake
people often make is that they don’t allow their model to
drift with the thermal, which causes them to fall out of
the front or side of the thermal as it drifts downwind. If
this happens, then you need to look again and re-acquire
the thermal.
in-Flight adjustments for
performance and conditions
• Pitch Attitude
• Minimum Sink Speed
• Maximum Lift/Drag (L/D) Speed
• Best Penetration Speed
Once the fundamentals of launch, trim and control of
the model are learned, it’s time to consider getting the
most out of its ability to perform. To do that, you must
learn how to trim your model for maximum performance,
whatever the current conditions are at the time. The key
to trimming for maximum performance is to become
knowledgeable about, or aware of, three key speeds:
minimum sink, maximum lift/drag (L/D) and best
penetration.
These three speeds are what we call airspeeds, not
ground speeds (the aircraft’s speed across the ground).
Thus, the airspeed of the plane is relative to the air
mass surrounding it.
Pitch attitude
To determine the airspeed, you will have to watch
carefully for its pitch attitude. Pitch attitude can best
be described as the amount (degree) the nose of the
aircraft is above or below a line relative to the horizon.
The angle of attack term is used to describe the angle
between the chord (width) of the wing and the direction
the wing moves through the air.
Pitch
Attitude
Longitudinal
Axis
Nose
Center of
Gravity
Horizon
Line Relative to Horizon
Relative Wind Direction
Increasing Angle of Attack