Radio Control Soaring - 2006/01

CONGRATULATIONS TO everyone who
competed in the 2005 Nationals. A special
thanks to Jim Bacus who kept us informed as
the event progressed. This was a huge
commitment of time and energy after flying
all day in the heat, humidity, and often tough
conditions.
On the topic of tough conditions, this month
I’m going to write about those pesky rising
columns of air we call thermals. On occasion
they are our friends, and on others they vex
us with their size and unpredictability. I
won’t go into a technical description of a
thermal, but I will cover the techniques for
recognizing and then flying them.
In Arizona, and probably most parts of
the country that have large expanses of dirt,
there are visible thermals we call “dust
devils.” Throughout the years I have
observed these to have three basic forms,
with little variance, one of which is a thin
shape resembling a #2 pencil. These dust
devils are often tall, extending quite high.
The second type has the typical tornado
shape. This kind is often lower than the thin
type in altitude but can be extremely high.
The third kind has a wide cylindrical
appearance. From my observations this
variety does not share the altitude of the
former two. Understanding these basic forms
will assist in recognizing and then setting up
to fly them.
Recognizing a thermal can be a tricky
proposition. Not only is the recognition
influenced by your model encountering
altitude, but also by the type of thermal.
From level cruising flight, a disruption of
the aircraft is your first indication that you
have possibly encountered a thermal. A rise
of a wing panel, lifting of the tail, yawing, or
a pitch-up of the nose is a strong indicator.
In some cases this reaction can be violent.
I have experienced thermals that have
completely rolled the airplane to inverted or
pitched the nose into near-vertical
orientation. This makes the decision about
what to do next easy; in other cases it is not
quite as easy. If the disruption is not so
pronounced, you’ve got some decisions to
make.
I try to plan that no one else in the air is
going to be of benefit to me. But I’m not
stupid either, so if there is a gaggle of
airplanes clearly going up, I’m there.
My general technique is to fly crosswind
from the launch in cruising mode and watch
a change in attitude. If it is not one of the
obvious violent signs, I will turn downwind
from the attitude change and fly back to the
area. The thermal should be going
downwind, right?
When I encounter it again, I begin a turn
and adjust as necessary to stay in the
thermal. Every effort should be made to
ensure that the turn is as coordinated as
possible, to maximize the model’s
efficiency. This often requires using more or
less rudder than you have in a preset mix.
Adjust your turns as necessary to stay in the
thermal. You should be aware of the wind
conditions and factor those into your
adjustments.
During the process, your timer should be
scanning the area for other activity in case
the thermal your model is in dissolves.
Remember the cardinal rule of thermal
flight: “Never leave rising air.” The caveat
to that is that if you are at the edge of your
visual range, better to be safe than sorry.
You gotta get back!
That was my basic technique. I have
enlisted the help of five-time World
Champion Daryl Perkins to discuss his
theory of thermaling. Following are some of
his thoughts.
“Darwin asked me to do a little write-up
on thermal entry, what I look for in the air,
reading the model, etc. I’m going to base
this on contest flying and optimizing a
contest type flight. I’m not going to go into
ground signs or how to read the air prior to
launch (enough has been written about that).
“At most of the contests we fly in there
are already airplanes in the air. These
airplanes are tools for the contest pilot. We
can use these to decide where we want to
fly—and sometimes where not to.
“Let’s assume we’ve just come off tow,
and we see a gaggle of sailplanes. Let’s even
assume they’re high. Do I go straight for the
gaggle? Nope. I will always go downwind of
the gaggle and come back toward.
“Why? Two reasons. Most TD [Thermal
Duration] pilots really don’t thermal very
well and even most of the top-rated pilots
tend to fly upwind out of thermals. So I’ll
usually go downwind and pop the good
stuff. This works probably 90% of the time.
“Now if I go downwind of the gaggle
and I don’t pop, I can then come back
straight toward. Coming in from behind the
thermal, I can see all the airplanes in that
thermal, read them, and pick and choose the
stronger air. I will use this technique
whether there is one sailplane in a thermal or
20. It works very well.
“Now, what do we do if we don’t see
anyone buoyant? We don’t like the air that
anyone has? Very simple: Don’t fly there! I
often see people come off tow and go to
where someone else is already struggling—
safety in numbers I guess. Big mistake!
“If there is a bunch of airplanes or one
airplane coming down, Go the other way!
Go 180° from where the bad air is. You’ll be
surprised how often you’ll pop just by doing
this.
“Okay, now we’ll address every
sandbagger’s and contest flier’s nightmare:
no airplanes in the air, we have to pick our
own air, and we have no idea which
direction to go. The tendency is to come off
tow and go straight upwind. I typically don’t
like this. It’s hard to read a model upwind.
“I’ll come off tow and pick a direction
usually between 45° and 90° off of the
upwind direction. Left/right—doesn’t
matter, but I’ll be flying somewhat
crosswind. I’ll just let the model go. Trim it
for a little bit of cruise, not maximum L/D
necessarily, and not minimum sink, but
somewhere in between. Stay off the sticks
and let it fly. The airplane will tell you
where the air is.
“Ever notice how sluggish a model feels
in sink? Conversely, it gets just as lively in
lift. As we fly in one particular heading, it
becomes very easy to read the model. We
can see the wings bobble or the tail yaw in a
particular direction.
“Hint: If we are abeam a thermal, the
vertical fin will be pulled toward that
thermal. So if the fin gets pulled to the left,
roll slightly toward the left (not 90°, just
slightly) and see what happens.
“The biggest mistake I see here with
most contest fliers is they come off tow and
wallow to the left, wallow to the right,
airspeed increases, they then slow up,
sailplane wallows some more. How the heck
are you supposed to read a model when
flying like this? You’ll notice all the top
pilots pick a heading, stick to it, pick an
energy, stick to it, and let it fly.
“Okay, now we’ve bungled our way into
a thermal. What do we do now?
“There have been some articles written
about flying all the way through a thermal to
define it. No. If I’m going up, I’m happy. But
I won’t get complacent.
“I will slow up and start to circle, usually a
fairly large circle. I’ll do this to read the
energy all the way around. I will constantly
thermal.
“When I say extend, I rarely straighten
out and fly straight once I’ve started
circling. I’ll just open up the circle in the
direction of the better air, maybe onequarter
diameter, maybe half diameter.
Remember, the goal in a contest isn’t to get
high, but to make your target time.
“As I get more and more comfortable
and I’ve decided the thermal is going to
hold together, I will then begin to define the
really strong parts, or the core, of the
thermal. And I’ll optimize my climb
accordingly.
“Most pilots tend to have one diameter
thermal turn they tend to fly. They bank
over at 45° no matter what the air is doing,
or whatever, and keep it circling. This isn’t
the way to optimize our climb. Every
thermal is different and needs to be flown
differently.
“The key is how to fly so we climb the
fastest: big, lazy circles and shallow bank
angles? Small, tight circles staying in the
tiny core of a thermal? Or somewhere in
between?
“Ever notice how the top pilots climb
right through you? Once in a thermal,
they’re defining the strong spots and
optimizing their climb rates. They’ll fly
almost as slow as the model will
comfortably fly (minimum sink), with a
constant bank angle, and constant energy.
“If you use any one of these techniques,
I guarantee you’ll make your times more
consistently. Use them all; you still won’t
beat me. I didn’t tell you everything I know
… ”
That’s it for this month. Next month I’ll
carry this discussion a little further and then
begin the “after the thermal” process and
setup for landing.