Thermaling Tips - by Wayne Hobbs
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.
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
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
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.
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!
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
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.
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
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
More Thermaling Tips - by James Freeman
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
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.
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
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
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
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 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.
given day thermals tend to remain similar in nature, unless of course there
is a large change in conditions.
2) Bank angle
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
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
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
Some pilots have a better natural feel
than others, but don't despair its really quite straight forward.
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.
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
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
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.
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.
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.
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
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
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.
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.
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
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
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
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
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 Freeman10/1999