|Thermals part 3 - Thermalling Technique|
Will Gadd, in a series of three articles, shares his thoughts on thermals and thermalling. This third part deals with staying in and flying thermals.
Vol bivvied 800km across the North Amerian Rockies with Gavin McClurg over 35 days. National Geographic 'Adventurer of the year 2014/15'
My favorite part of flying is undoubtedly thermalling; in fact, thermalling may be my favorite thing to do in life. There’s nothing like hooking a sharp-edged, positive ripper of a thermal and riding it upward for a couple of miles. My least favorite part of flying is also thermalling; those days when everyone else goes up flying straight and you hit the deck like a dropped park bench--repeatedly. On those days you’re glad you landed alone so no one else can hear you scream. The following is my latest “thermalling system.” I hope it helps you develop yours.
A little more thermal theory is useful to understand how to fly them. I believe thermals close to the ground are often quite small and relatively violent. As they rise they tend to smooth out and expand. Pressure also tends to influence thermal formation; high-pressure days tend to produce smaller, sharp-edged, “punchy” thermals. Lower-pressure days can produce very strong thermals obviously, but they tend to have mellower edges and be larger in size.
The day’s lapse rate also influences thermal strength; a hot day with a very strong lapse rate will produce stronger thermals. Think of a very warm piece of air rising out of a collector on a day with a strong difference in air temperatures between the ground and say 5,000 feet above it. A thermal will rise quite quickly in this situation. An inversion is the opposite, and not surprisingly thermals usually stop or at least slow down at inversions.
The above factors (and hundreds more but this is a start) give each day its thermal “profile.” If you launch on a clear blue day (indicating high pressure) with a good lapse rate (you checked the day’s soundings), then you might expect sharp-edged, strong thermals. If, however, the sky is filled with soft cumulus and looks somewhat hazy due to moisture, then you might expect softer thermals. The first thermal of the day provides some good clues about what’s happening; if it rips you upward and all you have to do to stay in it all the way to base is turn a bit then you’re off to a good start. If it’s small and difficult to stay in then ends abruptly 1000 feet later and you can’t take it any higher, then you know the day will be more difficult.
I take a mental note of three important characteristics with each thermal I use during the day. What is my average climb rate? Not the spikes, but the true climb rate as expressed by a 20-second average? How high do I get before it totally falls apart, and are there any altitudes that seem tricky to keep climbing through? And finally, what are the size and drift of the circles I’m making?
The climb rate tells you what to expect as the day progresses; climb rates tend to improve until late in the day, and thermal size also tends to increase as the day wears on (sink too unfortunately). If you’re getting solid 600fpm climbs, then it’s probably not worth stopping in 100fpm on a glide unless you’re low (anything going up when you’re low is great). The peak thermal altitude is also useful; if you are getting to 6,000 feet AGL consistently but a strong thermal suddenly “stops” at 4,000 AGL then you’ve probably lost it and should search for it. However, if the thermal stops at 5,800 feet then it’s most likely done and time to go on glide. Remember that the peak altitude of the thermals should increase as the day progresses. On good days in Texas it’s not uncommon to see thermals in the morning only reach 4000 AGL, then 6000 AGL at noon, 10,000 at 2:00 p.m. and 14,000 at 5:00 p.m. This progression is generally less in the mountains but still observable.
Finally, the size and drift of your circles at various altitudes also tells you what to expect on the next climb and information on wind speeds aloft. This tells you what angle your thermal will be flowing from a collector so you can intersect that line I (note-very strong thermals will have no problem pushing the wind around them like a bridge abutment in the river).
OK, so you’re flying along and your vario starts beeping with the good noises. What to do? First, did your glider surge forward or fall back behind you just before the beeps? If it went behind you then you’re probably dealing with a “gust.” Wait and see if the beeping continues or goes back to sink. If it’s a thermal and the beeping increases, turn. I don’t worry too much about which direction; if one side of the glider is noticeably more pressurized or higher above you, then lean meaningfully in that direction and pull on the brake smoothly. How much pull ? Higher pressures in your glider indicate a stronger thermal, meaning you can pull harder you can. However, the most common mistake in thermalling is to pull too aggressively on the inside brake. When you pull too hard on the inside brake your body tends to swing to the outside of your turn in a small wing-over. Then your body swings back under the glider, you lose the turn and fly straight out of the thermal. Many pilots then crank another wild-ass turn to try and get back into the thermal; I flew this way for about five years before getting it figured out.
What you want to do is fly in a “coordinated” banked turn. This is like riding a bicycle; you and the bike are at the correct bank angle for your speed and the sharpness of the turn. One of the most common problems pilots have is maintaining a consistent circle while thermalling; I expect you know what I mean… The correct technique is to start a turn with a smooth, controlled lean and simultaneous progressive inside brake application. The glider will bank up, your body will follow it, and due to centrifugal force you will continue to stay outside the glider’s circle and smoothly ride the thermal up. Jerking the brake instead of applying smooth increasing pressure will just swing you to the outside of the glider--then you’ll swing back under it, repeat. The glider will also remain over your head in a true coordinated turn; if it falls behind you, reduce brake. If it threatens to surge in front of you, apply a quick correction while maintaining your lean and turn.
If you can’t figure out what I mean, pull on one brake sharply and release it; you’ll swing out from your glider then back under it, usually with an oscillation or two as a bonus. Then try leaning hard for a second or two then go back to neutral lean; you’ll swing out to the side of your glider then back under it, but not as much. Now smoothly lean, pull gently and progressively on the brake and hold it; you’ll enter a gentle spiral dive or circle, same thing. This is what you want.
Airspeed and bank angle are directly related; the higher the bank angle, the more airspeed you need to keep the turn coordinated (think of a spiral dive). The lower the bank angle, the less airspeed you’ll feel on your face. Thermals are seldom perfectly consistent; this means you will have to continually adjust your brake and lean to maintain a coordinated turn. If your airspeed starts decreasing and the glider levels out, lean a little more, let up on the outside brake a little bit, and increase your airspeed and bank angle. If your air speed increases suddenly, lean a little less, pull a bit more on the outside brake, and maintain your bank angle. If you can learn how to thermal in a coordinated bank then you are well on your way to thermalling efficiently.
OK, so your vario is beeping like mad; how long do you wait before turning? If the day’s thermals are small and you’re low, start turning immediately after you’re sure you’ve hit something (not just a gust). Rules of thumb about waiting two seconds etc. are meaningless in my experience. You’ve found lift, initiate a smooth banked turn and see what happens. If you climb really well for a quarter circle and then start sinking, open your circle up a little bit in the direction you found the best lift then tighten as the lift increases; notice the pressure in your wing and how your butt feels in the seat, not just the vario beeping, these are critical clues.
Listen to the noise in your ears as well; with practice, you can actually hear the different air flows as you fly through lift or sink; if you can’t hear the air then get a new helmet. At some point in your circle everything will add up to the best lift as defined by your vario, wing pressure and lift under your butt. If you’re flying a coordinated 360 then it’s relatively easy to develop a mental map of where the best lift is in each 360; don’t worry about the ground, but where you encounter the best lift within each circle. Try to develop a “mental map” of what’s happening in each 360.
To fly toward better lift, maintain a coordinated turn, just reduce the bank slightly as you come back around the 360 and move the center of your circle over a little bit toward where you got the best lift. NEVER STOP CIRCLING. Once in the best lift, tighten the circle up slightly while maintaining a coordinated turn. Perhaps you get solid lift for half the turn, general sink for half the turn. Move the circle in the direction of the best lift again. Now you get solid lift for three quarters of the turn and less lift for one quarter. Move it again. Now you’re climbing solidly for the full revolution of your turn at +400 fpm average, but one portion of your circle is going up at +600 and another at only +200.
If you weren’t in a coordinated turn, and most pilots aren’t, this would probably be due to the oscillations inherent in thermalling in an uncoordinated turn and you would not have a clue what’s actually going on. But you know to thermal in a coordinated manner, so you move your circle toward the +600 and eventually lock in a perfect 1000fpm climb all the way to base.
Irregular thermals may give irregular “instantaneous” readings on your vario, so focus on getting the best average climb rate that you can. Hang gliders and sailplanes can use all kinds of funky ovals and figure-eights to get better average climbs, but I have found paragliders climb best flying coordinated, continuously adjusted circles (or straight if the thermal is big enough!).
I find I thermal with 30-45 or more degrees of bank on days with small, strong thermals, 15 to 30 on lower pressure days and almost flat on days with light, wide thermals. The extremes of bank angles come in dust devils (almost vertical) versus flying straight and flat while climbing like mad under a big cloud; somewhere between these two extremes is the correct angle for your thermal on that day. Every glider responds differently to brake force and the amount of lean; what works for one pilot on his glider usually has little to nothing to do with yours. However, every glider will circle in a coordinated manner, and the feeling is unmistakable once you get it.
Here are a few scenarios to help pick bank angles for thermalling. Say you’re flying along in -600 fpm and suddenly you’re screaming up at +800. You turn, then go down at -400,so you move your circle toward the +800 but can’t lock it in despite continually re-centering your circle. You probably need a higher bank angle and smaller circle. If you’re very low in a small thermal, you may only be able to get half a turn in. Do your best to just improve how much of each circle you spend in lift, you’ll lock it eventually as you climb.
Another scenario: you’re flying along in -600 when your sink rate starts to decrease smoothly to zero sink, then +200, then +300. I would keep flying straight until the lift starts to decrease, then initiate a relatively gentle bank and center on the best average climb rate. A relatively gradual, consistent rise in your climb rate is a sign of a large thermal. Often you can find very strong cores in large thermals that will offer much higher rates of climb, but in general the larger the thermal, the less bank angle the better to maximize your climb rate. Some bank angle is usually good; a glider won’t turn in a coordinated circle without it, but you can fly in a coordinated turn with equal brake using lean; watch a good pilot fly and you can tell he or she is often controlling the glider primarily with lean and modest adjustments to the outside brake.
There is no correct number of pounds to pull on your brakes while thermalling or distance to pull them down (1/4 brake is meaningless across a range of gliders), but there is a correct amount of brake to pull and lean to maintain a coordinated turn. It’s like riding a bike; no one can tell you how to do it, but you stay upright when it works. I generally thermal with roughly twice the amount of brake pressure on the inside brake than the outside, and adjust my turn primarily with lean and the outside brake. You will probably do it differently, but know a good coordinated turn when you hit one.
Don’t change directions when thermalling, especially when low. There are three good reasons for this; First, changing directions messes your coordinated turn up and you have to fly straight for some time between turns which usually takes you away from the lift (all directions but one lead away from the lift…). Second, you lose your mental “map” of where the best part of your circle was. Third, the direction change will cause your vario to beep in all kinds of interesting but non-helpful ways. It is almost always better to simply move your circle over toward the better lift than try to switch directions and fly toward it.
If you’re having a hard time maintaining a coordinated turn, try flying a bit faster; use more lean and less inside and outside brake. Many pilots try to fly a perfectly flat circle; in truly massive lift this works well, and your glider may have its best sink rate with a fair amount of brake on. However, I find flying a bit faster with a mild bank often enables me to lock in the thermal’s best lift. Don’t confuse what works well while ridge soaring with what works best thermalling, it’s a very different game.
First, know if you’re at the top of the thermal or not. If every thermal so far has ended at 6,000 AGL and you’re at 5,700 then forget about it and go on glide. But if you’re climbing well at 3,000 AGL and lose the thermal then it’s time to go into search mode. If there’s any wind at all, the thermal is probably either directly down or upwind of you. The first thing to do is expand the size of your circle and pay attention to your mental map. If you were climbing at +200 fpm and then start sinking at -600 on the upwind portion of the 360, open the circle up back downwind. If the sink improves to -400 and then -200, move it even more downwind. If nothing good happens, try moving upwind; again, an improvement in sink is as as relevant as finding more lift, work toward the area of lesser sink. Also pay attention to your groundspeed; it will generally increase as you follow the air flowing into a thermal, but decrease if you’re bucking the wind flowing into a thermal by flying away from it (remember that thermals, especially when low, pull or entrain air into them). If I’m low on windy days I tend to fall out the upwind edge of the thermal. If I’m high on a windy day I tend to fall out the downwind edge of the thermal. I have no idea why, but that’s how it works.
I’ve seldom encountered thermals that are smooth cylinders from the ground to base; the trick is to follow your vario, wing and seat pressure up in the best lift with continual gentle adjustments to your coordinated circle.
If the outside of your wing loses pressure suddenly and ruffles or takes a mild collapse, you’ve just found a relative difference in lift. Perhaps you’re in +600 and your outside wing just hit some +50; you want to move your circle away from the area you just took the turbulence in and toward the better lift. If you’re thermalling in a gaggle and see someone take an outside wing deflation ahead of you in the circle, then it’s probably worth tightening your circle away from that area and then opening it slightly to fly toward the better lift, tightening the circle as you encounter better lift. Most pilots tend to fly the “pattern” in a thermal rather than really watching the climb rates of the other gliders; if everyone climbs better in one half of their circle than the other, move your circle toward the better lift; you’ll climb above the other gliders quite quickly using this tactic. If someone is out-climbing you off to one side then move your circle to them; there’s no heroism in climbing slowly by yourself.
If you see the glider in front of you in a gaggle start climbing like mad, you may want to start tightening your circle immediately so you are in a higher bank angle as you hit the rising air and can “grab” more of it; again, fly the thermal, not the other pilots.
Look for pollen, plastic bags, bugs and other debris in your thermal. Birds in general and Swifts in particular will almost always be in the best part of a thermal; follow them immediately. Swifts and other small birds seem to eat the bugs that are drawn into thermals; if you see a group of them swarming upward, jump in with them even if doing so requires a short glide. Because thermals are pulling air into them, trash often automatically centers itself in a thermal; I’ve climbed thousands of feet in the company of newspapers or other debris.
Some days produce thermals that seem to want to spit you out; most of the time I’ve found that this is due to flying with too large a circle. Think of a spout of water shooting upward; if you stick your wing into the center and keep your circle within the column, you’ll go up. But find the edge and you’ll lose pressure on the outside of your wing. This creates drag, you lose your bank angle and tend to get “pulled” out to the side.
Try flying with your vario turned off; Chris Mueller and many other top pilots often fly long distances without their varios ! I don’t want to get too esoteric here, but how your glider feels in lift becomes clear if you focus on the clues. Turning your vario off forces you to pay attention to what’s really happening with your glider in different currents of air. I’ve learned a lot in the last year by playing this game, especially in gaggles where I can watch other gliders.
The smoothest air is often right in the core of a strong thermal, and your glider will be more pressurized and stable if you are flying a higher bank angle; if I’m climbing quite fast, I know that the edge of the thermal is likely to be quite turbulent. I’ve never flown away from a very strong thermal as I know I’ll hit turbulence doing so; the best thing you can do is lock into the core and take it to base.
The most extreme variations between sink and lift tend to be below five hundred feet off the deck; you’re flying along in 600 down and suddenly you’re ripping at 1000 up, then falling out of the sky again. However, the best true average climb rates tend to be higher in the thermal until it cools to the point where it won’t give you any more lift. I often will see spikes of over 1500 fpm low to the ground on days where I can’t get more than 600fpm climbs on the 20-second averager. A thermal’s real climb rate is what you can get out of it on the averager, not the “spikes.”
I often hear pilots say, “Dude, I got 2000 fpm today!” They are almost invariably referring to the lift spikes and not their true rate of climb. The only place in the world I’ve seen true 2000fpm climbs is the Owens Valley in July, but crank a hard uncoordinated turn and you can easily create your own 1000+fpm “thermal” as your vario swings up and beeps happily; this is a lie, but many pilots will believe it and keep creating their own thermals with wild turns where there is nothing.