How to survive thermalling in crowds?

by Joe Greblo


    Kagel Mountain, world famous for its consistent soaring conditions, is equally famous for its crowded airspace. Many who fly here will agree that during crowded conditions it is very difficult to relax and enjoy a flight, for fear of an all to close encounter with another glider. Heated complaints about right of way violations are common topics in post flight discussions. This article will not discuss basic thermalling technique, or simple right of way rules. Plenty has been written on those subjects already. Instead, I'd like to concentrate on specific problems encountered at Kagel Mtn. on crowded afternoons.

    The main problem is not necessarily too many gliders in the air, but rather the different flying styles, thermalling techniques, and right of way procedures of many pilots. It's this lack of uniformity in the flying styles of our local pilots that makes the site seem more crowded than it really is. Consider for a moment how 200 people can safely ice skate at a crowded rink IF everyone conforms to basic patterns of speed and direction. But remove 100 of those skaters and send the remaining 100 on the ice to race around in any speed and direction they wish, and the ensuing ice anarchy would result in utter chaos!

    This article is designed to help you understand air conflicts and their causes. As you shall see, some of these causes are not real obvious. By analyzing these situations in advance, you can prepare yourself to avoid most aerial conflicts, and maybe even a mid-air collision.
Keep in mind these 2 main ideas as you read this article. First, Kagel Mtn is primarily a thermal site. The bowls are actually ridge soarable during thermal gusts, and on occasion the whole ridge is soarable. This does not mean that you should ridge soar this site. Second, when flying in crowded conditions, personal flying style must be sacrificed to some extent to accommodate the "gaggle" as a whole.


    The simple rule, "THERMAL IN THE SAME DIRECTION", is broken more often than any other. Unfortunately, this rule is not as simple as it appears.

There are four basic reasons why pilots find themselves in the same thermal, but thermalling in opposite directions.

1. Not looking or thinking far enough ahead. Flying in crowds requires plenty of in-flight, on the spot planning. It is imperative to know which gliders lie near your path and what direction they are turning. If thermalling or flying in turbulence is so mentally taxing that it requires near total concentration, then it's best to avoid thermalling near other pilots. Practice thermalling in an area free of crowds until your skill and confidence provide plenty of "left over" concentration for planning ahead.

2. Hi-low split. As in the card game, the losers are the guys in the middle. Envision yourself already low when a sink cycle hits. Your search the ridge as long as altitude permits, but are eventually forced to head out toward the LZ. Just ahead and 200 m (600ft). above you, you notice a pilot circling to the left and climbing steadily. He is so high that you are not sure exactly when and where you will enter the lower part of his thermal. When you find the lift, your right wing rises so you turn right, opposite the upper pilot's direction. You reason that since he is way higher than you, he won't mind if you circle in the wrong direction. Besides, your too low to turn left and fumble through the sink before re-entering the same thermal.

    Sure, the other pilot may not mind because there is no immediate conflict. But think ahead a little; it's a crowded day, and this sink cycle will force every other pilot in the neighborhood to head for your thermal just as soon as they see you climbing. You might as well paint a bulls-eye on your helmet. The plot thickens (literally) as the pilots, arriving low, follow you and circle right, and the pilots closer to the upper glider follow his lead and circle left. Pity the poor fools in the middle. They're all busy screaming at each other to turn the other way. And since you were well below this mayhem, you got off "scott free". In fact, you never even knew that you may have almost caused a mid-air.
    In this situation, entering the thermal at low altitude, you would have been fine turning the wrong direction, ONLY IF you could reverse your turns to coincide with the pilot above WELL BEFORE any other pilots arrived on the scene.

3. Thermals with multiple cores often cause pilots to meet thermalling in the wrong direction. Let's look at an example: It's a crowded Sunday, and you've hooked a good one in front of launch. Your climbing at 0.5-1.5 m/s (100-300fpm) up. You're circling to the left, trying to core a little tighter and get a steadier reading on your vario. A hundred yards in front of the ridge you notice another pilot turning right, climbing at about the same rate. It seems like there's plenty of distance between the two gliders, so you continue to work the lift. Within minutes however, the other pilot's wing tip rockets by your control bar. WHEW, A CLOSE CALL! How did he end up so close?
    A Multiple core thermal is often interpreted as two or more separate and distinct thermals. Since these cores are all part of the same unstable mass of air, they often behave differently than the thermal as a whole. The cores sometime seem to wander unpredictably within the thermal mass, often merging with other cores. Two pilots circling in separate cores within a single thermal may find their 2 cores merging into one. When flying with another pilot in what may be a multiple core thermal, it is often best to turn larger circles which pass through the different cores. If your comrad insists on working his core, consider working it with him if it's large enough. If not, search elsewhere for a safer, more predictable environment.

4. Merging thermals. This is the one that I fell for, even after I watched it happen to others at Kagel. It happens often at this site. 
I ventured over to nearby Trash Mtn on a single surface glider, only to sink out. There was a pretty stiff south wind and I was concerned about reaching the LZ. Instead of trying to make the glide out, I decided to turn back towards the Kagel ridge in a last ditch effort to get back up. My logic was that I could fly cross-wind to the "volcano" and hopefully find lift. If not, I would continue to the base of the dam and land in the alternate LZ.

    I found some zero sink over flat ground and started turning left. There was no one above me. The nearest glider was up against the Kagel ridge nearly a quarter mile downwind of me. Because of his distance, I paid little attention to the direction he was turning. I was drifting back fast and hardly climbing. I didn't want to lose this thermal now since I was definitely too low and too far back to make the usual landing area. As I approached the wall of the Kagel ridge, my climb rate rose dramatically and my drift slowed. At that moment I didn't realize that I was almost directly below the glider that earlier was quite a distance away. We were separated by several hundred vertical feet, and although I didn't know it at the time, he was turning in the opposite direction. The problem became apparent when a 3rd glider pilot attempted to enter the thermal at an altitude mid-way between us. Frustrated at not knowing which direction to turn, he left in search of another thermal. Later upon landing, he was quick to remind me of the incident.

    How did I end up directly beneath a glider that moments earlier was in another thermal nearly 1/4 mile away? Thermals over flat ground drift much faster than thermals up against a mountain slope. The pilot that entered the thermal near the ridge drifted slowly. I entered a thermal over flat terrain and drifted quickly. Soon I was under him. Our separate thermals had merged in to one. Had I realized this while it was happening, I would have reversed my direction much earlier in anticipation of my approach to the other pilot. Conversely, if the other pilot had been paying more attention, he could have easily reversed directions prior to the arrival of pilot number 3.


    How many of us have been trying to thermal up the ridge at Kagel Mtn. on an unstable day and run across a ridge soaring pilot? He's the guy who does tight figure eights over a thermal-filled bowl because he thinks he's experiencing ridge lift. Then, when the thermal gust dies out, he heads off to the next bowl, where if he's lucky, he'll find other pilots to chase from their thermals.

    Ridge soaring is ridge soaring, thermalling is thermalling, and never the two shall meet. what I mean is, using ridge soaring techniques at a thermal site where others are thermalling is about as compatible as slow dancing at a rhumba contest. If you are alone on the ridge, by all means ridge soar to your hearts content, but if you see other gliders coming your way, its necessary to utilize thermal techniques. If you're too low to negotiate a safe 360, then fly out from the ridge in search of another thermal.


    General right of way rules are available in many soaring books, especially those written by Dennis Pagan. Unfortunately, the real world of hang gliding does not always follow ideal textbook situations. It's not cut and dry. Of course you veer to the right if you're about to careen into another aircraft head on. And certainly the low pilot has the right of way, but how does one pass-by another pilot in a thermal or join him, without scaring the heck out of him?

    It isn't enough simply to fly by, taking care not to run into him. There's more to it than that. You need to fly by him in the least intimidating manner possible. You need to give him confidence that you know what you are doing and that you won't run into him. You can do this by establishing a flight heading that is well outside of his projected flying circle. In other words, fly around his thermal, not through it. This allows him to concentrate less on you and more on his own job of flying. 

But what if you want to enter a thermal already occupied by another pilot? 




    When at similar altitudes, learn to enter another pilot's thermal on nearly the opposite side of his circle. Exactly opposite isn't as safe because each pilots' view of one another is blocked by their lower wing. Entering too close to the other pilot's tail forces him to rubberneck well behind his wing to see you. If you enter too close to his nose, you'll be forced to do the same. This also makes it hard to scan for other pilots who also might be trying to enter the thermal. The perfect position to enter the thermal allows each of you to maintain eye contact while looking in front of your lower leading edge. It's difficult to maintain this position in choppy thermals, but the better you get at it the more confident you will be when sharing thermals with other, and the more confident they will be when thermalling with you.

    Three or more gliders in a thermal at the same altitude is not a very safe or comfortable situation. Unless you are experienced in this situation, avoid it like the plague. Since it's likely all three pilots cannot see each other all the time, it's absolutely crucial that each pilot maintain consistent airspeeds and bank angles. Sudden and unpredictable changes in anyones flight path could spell instant disaster.

    More often than not you will enter an occupied thermal below or above another pilot. Cherish this short lived moment, for soon one of 3 things may happen. Either the other pilot will climb to your altitude, you will climb to his, or, you guessed it, someone else will enter your thermal. Remember that if someone is climbing from below and getting closer, he has restricted vision of what lies above and therefore has the right of way. If you are thermalling above an approaching pilot, widen your circle and allow him to climb through. You can always re-enter the thermal again after he is above you. It may hurt your pride to do so, but it's a whole lot classier than screaming at the other guy as if it's his fault.


    Flying in crowded conditions demands compatibility with other pilots and cooperative thermalling techniques. Try to maintain concentric circles even if this results in a slower climb rate. Avoid sudden bank angle and airspeed changes that may momentarily increase your rate of ascent. Rolling in or out in a "sudden pop" may take you up a litter quicker, but the other pilots in that thermal won't appreciate your unpredictable actions.


    Unclear signals are perhaps the most common errors made by pilots on crowded days. Although your glider is probably not equipped with turn signals, or a horn, you do have several devices at your disposal which can give clear, precise, signals of your intentions. Remember, it is not enough that you know where you are going. Other pilots must also be able to predict your actions if they are to comfortable flying with you. Clear :signals" of your actions are often nothing more than plenty of eye contact and well planned, predictable, maneuvers. When possible, make direction changes during periods of eye contact with your neighboring pilot, and avoid them when your are obstructed from his view. Turn your head toward the other pilot so that he will see your full face and know that you are looking directly at him.


    Thermalling in a "gaggle" is a full-time job, requiring 100% concentration on right of way, etiquette, and the airspace around you. If your skill level as a pilot requires all of your concentration just to stay aloft, then you won't have enough of that precious concentration left over to insure against a mid-air collision. Remember, priority #1 is safety, staying aloft comes second.

    The best way to evolve into flying in crowds is first to develop your thermalling skills well away from the maddening crowds. On crowded days this may mean out towards the l/z or at other less popular thermal sources such as the "volcano". Windsports offers free ground school instruction as well as reasonably priced advanced thermalling lessons. Only after you have learned to stay up without exercising a great deal of concentration should you attempt to thermal close to other pilots. The "buddy system" is a good way to polish some of these techniques. Make arrangements with a qualified pilot who is willing to fly with you in the same thermal and critique your performance and right of way skills. This way you will be able to spend your time developing you skills safely as well as efficiently.


    Since sites like Kagel Mtn. appeal to novice, intermediate, and advanced rated pilots, it is common to find all of the above thermalling in the same vicinity. The novice and intermediate pilots, hesitant to enter the crowded areas, often practice their thermalling technique away from the crowded areas; something I'm sure we all agree is a good idea. A problem arises when these pilots find the courage to venture cautiously into the more populated airspace.

    Intimidated by the crowds, these pilots often experiment by easing their way into the congested thermals. They linger just off-stage, and slip into the "pack" every now and then to have a go at thermalling with others. This is a particularly dangerous practice. The only thing worse than 10 pilots in one thermal is 9 pilots in the thermal, with one pilot darting in and out of the action. There's no middle ground here. You're either in the thermal with everyone else, or you must remain completely away, in an uncrowded area. Again, the best way to learn to thermal with others is with instruction, the next best way is with the "buddy system". 

    As you can see, thermalling in crowded conditions is far more complex than thermalling alone. To do do requires knowledge, skill, technique, and a willingness to cooperate. Pilots strong in these areas are no doubt the safest and easiest pilots to fly with. Practice these skills and you'll earn the respect of others and you'll find yourself welcome in even the tightest of circles.