Great Planes Spectra Electric Sailplane Kit - GPMA0540 - Manual (Page 34)

directly towards you from downwind without getting disori-
ented. At this point you can start to establish a "landing
pattern" and bring the sailplane in for a landing from down-
wind. Landing into the wind enables the plane to be flown as
slowly (ground speed) as possible for accurate and damage
free landings.
It is probably not a good idea to try and fly around at a low
altitude with the motor on during your first flights. This will
cause the plane's speed to increase and make the controls
more responsive which is just what a beginner does not need.
The SPECTRA will climb to altitude several times on a
single charge allowing you to have flights well over ten
minutes without finding a n y "lift''. You should be able to get
two "full" climbs above 500' on a single charge although
there are many factors controlling this.
THERMAL FLYING
Thermal soaring is one of the most intriguing of all
aspects of flying and the SPECTRA was designed to excel at
thermal soaring even in the hands of a novice. It can be hard
for the average person to understand how a plane can fly for
hours and gain altitude without the motor running!
the cooler, denser air forces its way underneath the warmer
air. As this warm air is forced upward it contacts the cooler
air of the higher altitudes and this larger temperature differ-
ence makes the thermal rise quicker. The thermal is gradually
cooled by the surrounding cooler air and its strength dimin-
ishes. Eventually the thermal stops rising and any moisture
contained in the once warm air condenses and forms a puffy
cumulus cloud. These clouds, which mark the tops of
thermals, are usually between 2000 and 5000 feet high.
TYPICAL THERMAL
Wind causes thermal
to drift downwind
FACTS ABOUT THERMALS
Thermals are a natural phenomenon that happen outside,
by the millions, every single day of the year. Thermals are
responsible for many things including forming several types
of clouds, creating breezes, and distributing plant seeds and
pollen. If you have ever seen a dust devil (which is nothing
more than a thermal that has picked up some dust), you have
seen a thermal in action. Their swirling action is very similar
to that of a tornado's but of course much gentler. Most
thermals have updrafts rising in the 200-700 feet per minute
range but they have been known to produce updrafts of over
5,000 feet per minute (that's over 50 miles/hour straight up!)
These strong thermals can rip a plane apart or carry the plane
out of sight before the pilot can get out of the updraft.
Thermals are formed by the uneven heating of the earth
and buildings, etc. by the sun. The darker colored surfaces
absorb heat faster than the lighter colors which reflect a great
deal of the sun's energy back into space. These darker areas
(plowed fields, asphalt parking lots, tar roofs, etc.) get warmer
than the lighter areas (lakes, grassy fields, forests, etc.). This
causes the air above the darker areas to be warmer than the air
over the lighter areas and the more buoyant warm air rises as
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 in diameter or less at
400' altitude.) compared to the rest of the sky, the sailplanes
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 plane to "bank" and
turn away from where we would like the plane to go.
When you are thermal soaring, try to fly as smoothly and
straight as possible. Trim the plane 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.
34