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FreeFlight Advice: Thermal techniques

Originally Posted on  October 3, 2013

Q: I’d love to hear your thoughts/tips for thermal soaring pilots, especially those new to it. I’m a low time h3, and still learning to find them, stay in them, establish the right bank, etc.

A: I’ll do my best to answer this, while still keeping it short enough for a single blog post.  In reality, finding thermals, staying in them, and climbing as efficiently as possible are three entirely independent topics for discussion.

First, we need to find a thermal.  If you have mountains, hills, or other topography… this is a bit easier.  The best analogy I have ever heard is to imagine taking a mold of the hills and mountains around you.  Now imagine you took that mold, flipped it upside down, and dipped it in water.  Visualize how the droplets of water will pool together in spots.  As these pools get bigger they get heavier, but instead of just dripping off the mold they will more likely slide along the “terrain” to the lowest part of the mold- which would be the peaks of the mountains.  Most mountains have several ridges and spines leading up to the peak, and the water droplets will flow along all of these, gathering at the peaks.  When enough water has gathered at a peak, it’s going to be too heavy to “hold on” and it will separate from the mold and fall to the floor.  The purpose of this visualization is to realize that warm air behaves much the same way.  Rarely does a thermal just ‘lift off’ where it formed, more often it will follow the path of least resistance, sliding along until breaking off is easier than sliding along.  This can be a little more complicated when you are flying flatlands, but the general principle is the same.  In the flats, you’re looking for contrasting colored fields (temperature differences)… like a brown plowed field next to a green crop field.  The brown field is going to gather heat, and as that warm arm drifts along the ground it will either break off when it it’s that green field, or it won’t.  If it doesn’t, you’re looking for the next piece of resistance it might hit… tree lines, tractors, trains coming through, anything that might help that air separate from the ground letting it rise up.  The water droplet analogy works in the flats as well… but it’s a bit harder.  In the mountains or the flats, try to account for the wind as well, which will “push” the warm air along the ground, and might affect where it ends up versus our wet mold visualization, which does not account for wind.  Finding thermals is part art, part instinct, and part science.  Thermals are just physics and fluid dynamics, science, and everything happens for a reason.  Rarely do we have enough info to know exactly what is happening, where it will happen, or why.  Luckily every time we fly we get to form a theory as to where thermals will be, and then test it out by going there.  It’s called experience, and after doing this hundreds of thousands of times you get much better at knowing what is likely to work, and what isn’t.

Once you find that thermal, you need to get in it and stay in it.  Sounds simple enough?  HA!  Few thermals will make it easy on you.  Thermals will speed up, slow down, drift faster than the wind, drift upwind, they can snake all over the place.  Like I said before, they are just following the path of least resistance, and it’s just science- cause and effect.  Not that knowing that is helpful, because we have no idea where the path of least resistance is… but still, it’s nice to know it’s not entirely ‘random’.  Most people visualize a thermal as a round column, with the strongest part in the middle.  These certainly exist, but that is a highly simplified model.  I find that most thermals have a lot in common, but also that no two are the same… which makes it very difficult to “teach” what really takes years of thermalling experience to learn.  No shortcuts for experience, and no amount of knowledge will substitute.  What I will say helped me immensely, is making my ‘goal’ while thermalling not to stay in the thermal, but to find a 360 that I can “hold” and climb at a pretty constant rate all the way around.  If you’re only climbing for half of your 360, you’re only half in the thermal.  If you’re climbing faster in one half than the other, you are either not centered, or turning too wide.  I find that 95% of pilots turn too wide.  Wide “sailplane” turns minimize your sink rate, but if it’s not keeping you in the lift- or the core- you’re missing out.  One thing that makes the sky-god thermal masters so good is that they know when to flatten out and when to tighten up.  It’s a bit of an intuitive thing, and again comes from experience.  Did I mention there’s no shortcuts for experience?

Once you can find and climb in thermals with consistency, it’s time to focus on climbing FASTER.  Thermals don’t last forever, and sometimes you need to get as much as possible out of it before it’s gone.  Many cross-country competitions and races are won or lost on the UP, much more so than on the glides.  Climbing efficiently is an art of flying as slow as possible, and banking as little as possible, while getting the tightest 360 possible.  There IS such a thing as flying too slow, by the way.  Because of the sweep and twist in our wings, it is possible to fly around with part of the wing stalled and not creating lift.  Lift is what we’re looking for here, so flying TOO slow (pushing out) is usually a losing proposition.  It’s also risky, because pitch stability decreases as CG moves aft… if you are slow, pushed out, and get spit out of of the thermal bad enough, you just might tumble.  Seriously.  And that is why I would focus on finding and climbing in thermals FIRST, and only once your seriously proficient with that should you worry about maximizing your climbs.  Some of the techniques used to maximize a climb require a good ‘feel’ for thermals, and identifying the characteristics of the thermal you are trying to maximize… and the ability to do this only comes with, you guessed it, experience!

Hope that helps!