Thermalling is an advanced flying skill that most pilots will encounter late
in their Hang 2 skill level, and really concentrate on as they enter their
Hang 3 rating.  I think from personal experience and from observation, that
there are many styles of thermalling.  Mine have changed over the years and
especially since I began flying an Exxtacy rigid wing.  Any of the advice
and techniques I list below may be heavily influenced by what I'm flying, so
take that into account when you try and translate it for your equipment.

As always, I bring up a topic like this to provide my own narrow minded view
but primarily to bring about discussion from many listees, who are far more
able to put into writing, what I intuitively understand, but can't always
verbalize.

I have been fortunate to have been around to read many great articles
written across a very long time span of Hang Gliding issues and some I have
re-read more than once.  I have also, and advise you to do so as well, read
many sailplane books on thermalling to help build my knowledge base.  I
still do so because just like you, I am also still learning.  From a
hanggliding consensus, some things that seem to be general rules are:

1.  The lower you are in altitude, the higher the bank angle you will need
to thermal at, to stay in the thermals, because they are likely to be small.
Better to over bank at first than to under bank.

2.  As you gain altitude, thermals often widen and strengthen, and you are
able to lower your bank angle and often obtain a better climb rate.

3.  Often I see pilots bank to quickly upon encountering lift and then fall
off the thermal as they do their down wind rotation.  A very good rule of
thumb is counting to 3 before you turn.  If  you are low, then quickly may
be your best option as you don't have time and altitude to spare.  If
higher, than you can afford to wait a little longer to explore the width of
the thermal before you turn.  I prefer waiting as I'd rather turn back for a
thermal that's behind me, than fall off the edge and lose altitude before I
can rotate back to the lift.

4.  Locating and staying within the thermal is often a tricky part of
thermalling and we use different tricks to do this.  One of the most
important for new pilots to start out using, I think, is to visually locate
a point on the ground below where you are thermalling so you can obtain a
reference point.  Recognizing that your thermal will drift with the
prevailing wind.  Strong thermals don't seem to drift as fast as the wind so
don't over estimate the drift rate.  If you lose your thermal, be sure and
do a search down wind and then upwind on your expected drift line.

5.  Instrument location is also an excellent way to thermal and especially
useful at higher altitudes.  It is the method I use, so don't fly close to
me when you see me thermalling!  In this method, you actually watch your
instrument climb rate and as it peaks in strength during your rotation, you
pick a point on the horizon off your outside wing and as you come back
around, you move your thermal circle in that direction.  Also keep in mind
that your instrument deck has a delay in it so a good pilot will recognize
that maximum lift actually occurred at a point slightly behind this visual
point and adjust his circle accordingly.

6.  The most efficient thermalling circle is one that is very concentric.  I
am speaking from a glider efficiency point of view.  It is also easier to
stay centered if you can circle concentrically.  Advanced pilots will often
change their bank angles constantly as they milk the pulses in a thermal.
I'd advise waiting a while on that technique as it can cause you to lose the
core.

7.  The most common mistake I see in recreational thermalling, is that
pilots fly through lift without testing it and giving up on lift to soon.
If you fly through some lift that is more than 2 seconds wide, and you have
a safe glide to a landing field, unless you have a visual reference of
something better, than I'd advise you to turn and explore what you just flew
through.  If you are in lift that is sustaining you, or allowing you to
climb, unless you have a visual reference of something better, than I'd
advise staying right where you are and continue to work and explore what you
have.  This is key to becoming a sky god!

8.  If the core is tight and strong, then I'd advise flying it in kind.
Meaning attack it with high bank and higher flying speed.  If the core is
broad and mellow lift, then fly it the same way, lower bank, lower speed,
and mellower.

9.  THE MOST IMPORTANT 100 FEET OF CLIMB IS YOUR FIRST 100 FEET!  I can't
emphasize this enough.  If you can climb 100 feet in a thermal, then it is
likely that you can climb out on that thermal.  The first 100 feet is
generally your hardest and longest, so really sink your teeth into it.  Get
mad if you need to .  Be aggressive.  Act as if you don't stay in this
thermal then you will have to go land (this might be true!).

10.  If you have landable fields down wind in the direction that you are
thermalling and drifting, then quit worrying about the landing field!  This
is also a very important lesson to learn and remember.

11.  Depending on your site, don't be afraid to drift up, over, and to the
back side of your hill as long as your are high and can stay safe from
rotors.  Ask your local mentors what they think is a safe altitude for the
wind conditions and your equipment.

12.  Learn to be patient in your thermalling.  It is very easy to climb and
then bail out down wind for distance and then find yourself on the ground
watching your more patient friends flying over and into the distance as you
break down.  Don't out fly the lift.  Unfortunately, I speak from experience
on this matter!

13.  Try and fly with, and like, those mentors who always seem to thermal
well and stay up the longest in the thermal conditions.  They must be doing
something right.

14.  Don't be afraid to be at high altitudes.  The rules of aerodynamics are
the same.  The higher you are, generally the safer you are.  It just doesn't
look that way.

15.  Be aware that learning how to thermal will be something you will be
working on for the next 50 years of your hang gliding career.  It is never
mastered, only improved upon!

There are many more, but these should give you newer pilots some food for
thought and hopefully others will add to, and correct, some of my
mis-explanations.

Safe thermalling.

Wayne Hobbs

Develop a mental picture of what a thermal looks like. Thermals are
rarely exactly like the textbook pictures. Watch some smoke rising from
an industrial smokestack, or fast motion film of clouds to visualise the
dynamic and somewhat chaotic movement of rising air. Thermals range from
short lived bubbles to columns extending from the ground to cloudbase.
They may be weak or strong. Some are wide, some narrow, some elongated
downwind. Add to your picture with experience.

As you approach a thermal you can expect to find quite strong sink. You
often run into alternating short 1-2 second surges of lift and sink as
you get closer. Next you will encounter lift.

In almost all thermals there is at least one and often several strong
cores of rapidly rising air surrounded by areas of more moderate lift.
To find the core you must first LOOK FOR IT. Too many pilots are simply
satisfied to be in lift and contentedly circle in 200 up when there is
800 up to be had nearby.

When you enter a thermal you should not stop and circle at the first
indication of lift (unless very low, thermals small, etc). Instead
continue flying into the thermal. Sometimes a wing may be lifted as the
strongly rising air in a core tries to push you away. Do not let this
happen! Turn towards the lifted wing to be rewarded with the stronger
lift. Alternatively the lift may peak and then drop off without any wing
lift if you fly straight through a core. As soon as the lift drops off
crank a turn.

Once you have found a core that's not the end. Expect to make minor bank
adjustments every circle to stay centred and often major adjustments
every 10 circles to stay in the best lift. Soaring birds rarely circle
in neat circles as they search out the best lift, neither should you.

If you have been circling in a core and then lose it you should have a
plan. The best one is to first look upwind first as you generally fall
out the downwind side (see books for explanation). Next look downwind.
Finally look crosswind. If there is no sign of the thermal after this
search move on, thermals can and do have bottoms that you can fall
through but unfortunately searching up is not an option!

Develop a clover leaf search pattern to explore thermals. Starting from
a circle in lift explore the four imaginary quadrants of the clover leaf
one at a time. You do this by extending your circles sequentially into
each quadrant. After each extension come back to the centre if better
lift is not found before going on to explore the next quadrant. In this
way you keep track of known lift while continually looking for better
lift.

Generally speaking at low altitudes thermals tend to narrower and more
bubble like. TIP - NEVER LEAVE LIFT LOW. At intermediate altitudes
thermals become wider and strong cores are often present. Towards the
top of a thermal lift often drops of while the thermal continues to get
wider. Often strong lift may be encountered near cloudbase (cloudsuck).
At the beginning of the day bubbles predominate. "Classic thermals"
occur during the peak of the day which depends on location but as a rule
peak ground heating (and hence thermal strength) is around 2.30pm LOCAL
SUN TIME. Towards evening smooth, wide weaker thermals are the norm.
Turbulence is generally worst during the peak of the day and often near
cloudbase.

Thermals are generated by buoyant air. Air becomes buoyant because it is
less dense than the surrounding air. Differential heating of the ground
causes differential heating of the layer of air above the ground. The
warmer air expands becoming less dense and thus buoyant. Perhaps
surprisingly the addition of water vapour also makes air buoyant. This
is because water vapour is 5/8th as dense as air. So in general we look
for areas that will be hotter and or have moisture added as likely
sources of thermals. Beware that to much moisture can have a detrimental
effect, whereas a little can have a very beneficial effect. A good way
to get a feel for this is just take a walk and observe the temperature -
if the air feels hotter then the surface you are walking over is a
likely THERMAL GENERATOR. Classic generators include dark ground, burnt
areas, tarmac roads/carparks, etc. Sand reflects heat so is bad. Some
crop paddocks get surprisingly hot, whereas others are cool. The vital
point to remember is the concept of differential heating - what you want
is a contrast. By a contrast I mean an area that will get hot next to or
better still surrounded by area which are cool. The edges of forests,
river banks and lake edges are all potentially good. Areas which heat up
fast are good at the beginning of the day. Areas which heat up more
slowly can be good towards the end of the day - for example you often
find thermals over forests later in the day.

Just because air is buoyant does not guarantee a thermal. Just as water
can cling to a ceiling until a drip forms so buoyant air can cling
stubbornly to the ground. Before anything happens it must be TRIGGERED
to release. A good analogy is to imagine that the ground is the ceiling
of a steam room. Anywhere you would expect water to drip from so you can
expect thermals to trigger from. In practical terms look for high
points. The flatter the ground the less significant the high point. In
the mountains ridge tops are good but in the flatlands treelines,
houses, rockpiles and even lonely telegraph poles all act as triggers.

Wind complicates the picture. Buoyant air can drift with the wind along
the ground until it is triggered far from where it was generated. In
this case sloping thermals result and you will tend to fall out the
downwind side unless you continually centre the core by flying upwind
(due to the fact that the thermal rises ~200 fpm faster than you do
because even though you are climbing up from the ground you are always
sinking down through the air. Alternatively the internal turbulence of
the moving mass of buoyant air may cause it to trigger independent of
ground features - in this case the thermals will be, perhaps
surprisingly, vertical because the source is moving with the wind.

Wind also influences the nature of thermals. Strong winds encourage
thermal triggering resulting in short lived bubble type thermals. The
air in areas which are protected from the wind can continue to get
hotter for longer before triggering - this often results in strong lee
side thermals. Crop paddocks often hold onto their heating airmass for
longer and can be better thermal generators than the classic ploughed
paddock in windy conditions.

Experience shows us that whenever the wind blows thermals will generally
be far longer downwind than they are wide, often with several cores
lined up downwind.

On any given day thermals tend to remain similar in nature, unless of
course there is a large change in conditions.

2) Bank angle

Good thermal pilots do not necessarily bank more or less than average
pilots. What they do do is bank as much as is required to position their
gliders in the core of the thermal.

Although some authors labour on about optimum bank angles the rule is
simple. Bank up enough to stay in the core! Experiment. More bank ->
better climb? -> continue banking it up. If more bank leads to a slower
climb then make shallower turns.

We expect small bubbles near the ground so expect to have to bank it up.
Late in the day wider thermals are the norm so shallower turns are
usually the go.

So how do you centre the core? There are several methods, of which I
will mention two.

The standard method is to tighten your turns when the lift drops off (to
bring the glider quickly back into the best lift) and to flatten the
turns as the lift increases (to fly into the best lift).

The pro method is to fly into the thermal, feel the glider react to the
air and then crank (bank it up) when you hit the core - more on this
next.

3) Feel

Some pilots have a better natural feel than others, but don't despair
its really quite straight forward.

As you correctly point out variometers have some lag. Sure some are
faster and more sensitive than others but as a tool FOR CENTERING
thermals they basically suck. Heresy to some no doubt but still true.

In a big gaggle at any given comp you will see pilots circling around
many different points. Why is it so? They can't all be in the core. The
fact that some pilots climb much faster proves the point. These
eccentric circles result from what I believe is a total over dependence
on variometers combined with the standard method for coring a thermal
described above.

OK, here is what happens. Consider a glider flying in a straight line at
24mph (36kmh/10 metres per second) straight across the centre of a
thermal. It will take this glider 9 seconds to traverse a thermal 90m in
diameter. Lets say this thermal has a 30m or 3 second wide core in the
centre. The glider enters thermal and is accelerated upwards. After a
lag of say 2 seconds the glider ascends far enough for the variometer to
note a change in air pressure and indicate a climb. Military studies
indicate it will take about 1 second for the pilot to process this
information by which time the glider has entered the core. A further 2+1
seconds elapse while the glider accelerates/pressure changes/pilot
assimilates change. Just as the pilot notes he is in the core he in
reality actually flies out of it. Using classical theory he decides to
bank it up when the vario indicates a drop off in lift. This occurs 2+1
seconds later just as the glider exits the thermal. The pilot now banks
up the glider which takes a further 2 seconds due to glider response
lag. At this stage the pilot  is actually 20m past the entire thermal!
You can continue this description on indefinitely however the point is
this:

"The classical method of centering a thermal will only work if there is
no lag in variometer response, pilot (processor) response, and glider
response"

So now we come to the secrets of thermaling - visualisation and feel.

The mark 1 accelerometer.

All of us come equipped with remarkably sensitive accelerometers which
are perfect for thermaling once we recognise both their power and
limitations. We can sense very small accelerations but feel nothing once
the acceleration ceases and we are moving at a constant velocity. Our
experience in our cars or in a lift shows us this. We feel the initial
acceleration but while travelling at constant velocity we feel nothing
until we feel the deceleration as we slow down. Our accelerometer is
excellent for thermaling.

Our second key ability is our power of visualisation. Just as we can
build up a mental picture of a dark room by wandering around bumping
into the furniture we can build a similar picture of the invisible
currents of air by flying around and bumping into them.

Here's how its done. Consider our pilot again. The instant he enters the
thermal he senses the acceleration. The instant he hits the core he uses
all his senses to note the strong surge of lift causing a strong
acceleration which combines with a tendency for the gliders nose to
pitch up to signal to his brain CORE! The one second processing lag
means he is still in the core when the message arrives. Two seconds
later he exits the core which he notes as a deceleration (like falling)
and the nose of the glider pitching down. One second for processing lag
and he initiates his turn. Two seconds later after response lag the
glider turns, but this time is still in the thermal.

OK so far so good but we are still going to be plagued by the dual
problems of processor and glider response lag. Here is where
visualisation takes over. The pilot now constructs a mental picture of
the thermal, where he is in it, where he is going, and finally what he
needs to do to centre his circle on the core. With each circle more
information is added to this mental map until coring becomes as easy as
driving round a round about. In simple terms say you are flying south
when you feel yourself fall out of the core. OK you think the core is
nore to the north so after a 180 you flatten out your turn for a couple
of seconds then resume your circle, you are now circling further to the
north and should be closer to the core.

Now we come to refinements. The first improvement is this. Pilot hits
core and processes it 1 second later. Knowing that the glider response
will lag 2 seconds he initiates an immediate turn - presto he is turning
in the core, admittedly perhaps not yet centred but still streets ahead.

The second improvement is to recognise the glider as the extension of
your body that it really is. Just as you can feel if I come up and push
you so you can feel if a thermal pushes your glider. But how do you tell
if a wing is being lifted and differentiate this from a wing which is
sinking on the other side, after all they will both result in a roll in
the same direction? Lift will be associated with an upward acceleration,
cause the gliders nose to pitch up, and if off to one side cause a wing
to rise. Sink or less lift (relative sink) will be associated with a
downwards acceleration (falling feeling), the gliders nose pitching
down, and if off to one side a cause a wing to drop. The bottom line is
that differentiating wing lift or drop doesn't actually make that much
difference. Why? Because in either case the glider is heading AWAY from
where you want it to go! Be your own boss. Don't let yourself be sucked
into sink and spat out of lift.

The next refinement is speed control. Linger in lift, speed through
sink. This goes for thermals to. Sometimes the core may be too small to
circle in. Sometimes the air is so bubbly there are no long lasting
cores. We can maximise the time spent in the lift by slowing down as
much as possible as soon as we sense lift. Our gliders make this easy
for us as the nose pitches up automatically. Don't fight it relax and
let it, depending on your speed and altitude (not at 50' please) slow
some more. Stall? Oh well slow a little less next time. You will be
surprised just how far you can push the bar out when banked up in a
strong core. Make sure you have enough height to recover from an
unintentional stall before experimenting.

So what is the role of the vario. Well once we are centred it will
happily chirp a continuous tone which is good because now we will get
limited feedback from other sources. It also remind us we are not
centred by showing oscillating lift strength.

There is no substitute for practice and the best way to see how you're
going is to go to competitions. You don't need a high performance glider
to have fun. I flew 185km (~115miles) in a Moyes XT intermediate glider
in my first comp. Ask questions. Read all you can. Buy a copy of Cross
Country Soaring by the late sailplane world champion Helmet Reichmann
from Amazon.com or the Soaring Society of America - it covers all of
this plus speed to fly in great detail.

Thermal Search Patterns

A few people have written to ask for a bit more info about search
patterns so here it is.

There are a number of circumstances where a search pattern is
particularly useful.

1 When you are low, desperate and in marginal lift
2 Whenever you lose the core
3 Even when you feel you are in a "core" to efficiently look for even
better lift

The first place I started to use a search pattern was making low saves.
You know the scenario. Gliding, gliding, gliding. Lower, lower and
lower. Finally you hit a few bumps and latch onto a workable bubble. You
are low so you can't afford to make too many mistakes or you will be on
the ground. The lighter the lift the better you need to perform. Once
you have found some lift you don't want to lose it right? But say you
have only found zero sink, or worse 50 down. You need something better,
but you still don't want to lose what you've got. After a few circles to
establish yourself it's time to go hunting. Sure some pilots just seem
to be able to feel which way to go but for mere mortals using a search
pattern is the way to go.

The essence of the search pattern technique is to NEVER lose track of
your known "good" lift. You maintain contact with this know lift by
centring your search pattern around it. Imagine this lift is situated at
the junction of an imaginary cross roads. The 4 imaginary "roads" which
lead away from this cross roads represent your search directions. What
you do is effectively explore a little way down each of the 4 "roads"
which lead away from this crossroads. If, after you explore a little way
down a "road" , better lift is not found you return to the crossroads,
maybe do a few reassuring circles, then try another road. If better lift
is found you circle in that then repeat you search using this new area
of better lift to search out from.

Typically a low save might go something like this. First you usually hit
a few bumps of alternating sink and lift (pilots usually refer to this
air as feeling live). Crank a turn as soon as any solid surge is felt
(using the MK I Accelerometer rather than the variometer). Consolidate
for a turn or two moving towards area where best surge of lift is felt
as acceleration up (not the same a best vario response due to lag).
Check variometer averager to see how you are going.  Allow heart beat to
return to normal if averager shows positive number but don't dawdle if
you've only achieved 50 down. Flatten turn and head in one direction
(say north) for say 3 seconds then do a 180 degree turn, fly south for 3
seconds then resume original circle. You have then explored ~100 feet to
the north of your known good lift before returning to your circle in
this lift. The same procedure can be used to search the other three main
directions (E, W, S). You can explore greater or lesser distances by
varying the time you fly straight  for. Provided you fly the same number
of seconds out and back and do an accurate 180 degree turn you should
never lose track of your area of known lift. You search distance should
be tailored to the expected size of thermals on the day, in the local
area, and at your altitude. Initially I usually make fairly nervous
little explorations before running back to circle in the centre. If
experience shows that the sink monster is not lurking nearby I get a
little more adventurous. Sometimes their simply is nothing better
nearby. If you already seem to be in the best available lift patience is
required and endless searching will just lose you altitude so you need
to use this technique with restraint.

When you're really low the direction of the first explorations can be
critical as you simply don't have enough altitude to explore far.
Typically this direction will be either:

1 A continuation of the direction I was going when I hit lift on the
basis that I was desperate and probably started turning before I got to
the thermal proper
2 Towards any wing lift or area where better climb is felt
3 Towards any circling birds, leaves, etc
4 Towards any likely trigger areas like tree lines, etc
5 Upwind as we tend to fall out the back side of thermals
6 According to the formula:

Turn Direction (in degrees magnetic)= [Dry adiabatic lapse rate +
altitude (in feet) - barometric pressure (in hectopascals) / 3 *log (#
fairies dancing on head of pin in local area)] + RND(n=360)

The benefits of adopting this search technique in low save conditions
are:

1 To maximise the chances of finding a good climb
2 To minimise the time taken to find the best climb going.
3 To minimise altitude loss and thus minimise the risk of decking it.

 A search pattern is the most effective way of ensuring that low save.
It is also a logical way to search for lost cores or look for better
lift during general thermaling. You will find the core more often if you
look for it. You are less likely to miss it if you do a logical search
pattern rather than blundering around hoping for the best.

If you look at racing a glider, or long distance XC it is in large part
a climbing contest. Inter thermal glides are definitely important
(indeed vital) but the fastest pilots over the course are invariably
amongst the fastest climbers. If you have ever been fortunate enough to
watch the really top pilots like Tomas Suchanek and Manfred Rhumer in
action you will see them continuously exploring for the best lift, but
usually not for long because they find it, out climb you, and are gone.
I once heard a pilot say  "As soon as Tomas flew into this 400 up
thermal it changed into an 800 up". Witchcraft? I think not. The truth
is that he led the other pilots into the core. Looking for and finding
the core, at whatever altitude, is just one of the many secrets of the
black art of thermaling.

Submitted by James Freeman 10/1999