Wayne Hobbs


    I noticed part of the way through the flight that I would be in lift with other gliders above me. Then, after a few turns I lost the thermal and noticed the other gliders were now way above me and quite a bit downwind. I may have been too focused on staying upwind of the field to let myself drift back with the thermal but I really just don’t think I had any kind of feel for the drift.
What advice do you all have about learning to feel and follow the drift of a thermal?

    Great question. Most likely you will recieve different answers, all of which will be correct but describing what you ask is a little like the blind men describing the elephant. Each perceives something a little different.

    Thermal tracking is one of the great challenges of our sport. There is no one simple answer, instead a variety of techniques and knowing when to use each.

    In general when down low, say below 300 m agl, I generally assume that the thermal drift will be in the general wind direction noted at ground level, but I also take into account what my mountain launch winds are in addition. In towing, you don’t have this second wind direction input. When low, I generally use the ground as a source of reference when I first encounter a thermal. When low, I almost always immediately begin turn initiation upon hitting any lift if I’ve been flying in calm to down air. I’d rather take a chance that this thermal is not large enough, than to risk missing the thermal. I immediately begin trying to center the thermal by noting where the strongest perceived lift was during my circle. I’ll then move my circle in the direction of where the I felt that the lift was the strongest during my last rotation. In each rotation I use this same method to continue to try and put myself into the strongest lift area. I fly with a flight deck and it has a very sensitive and fast responding digital instantaneous lift readout and I watch this as I circle and make a mental note of which part of the circle measured the best lift and then the next time as I rotate I’ll move my circle over in that direction by just slightly flattening my turn as my nose swings in that direction and then continue circling. I’m also noting my physical location and drift relative to ground based objects.

    As I climb higher and higher, I begin to ignore the ground based observations and begin concentrating on my flight deck and using the instrument more and more because the drift rate and drift direction will often change as one climbs up through the atmosphere.

    As a general rule, I’ll bank more steeply when I’m down low and flatten out my bank angle as I climb higher. In the area that I fly the thermals seem to be smaller, tighter, and stronger down low and get wider, smoother, and easier to circle in as they climb higher. The lift will also generally increase as the thermal ascends up to a certain altitude at which point the lift starts becoming broken and harder to stay in. This generally means your near the top of the thermal, but don’t give up as some thermals have the ability to bust through the inversion layer and continue on to much higher levels.

    While flying note the drift direction of any hawks, buzzards, or other pilots as they are great indicators of drift direction and drift rates at their altitudes and you should find similar drifts in your thermals at similar altitudes.

    Patience and practice are what make pilots good thermal pilots. Be sure and observe those pilots who seem to get up all the time. Watch how they thermal and emulate them. Go to the library and check out some sailplane books, they have some very good articles on thermalling and centering. The more you learn, the more tools you’ll have available in your quest for thermalling excellence.

    The more often you thermal, the better you will become as the learning self reinforces. If you go months between each thermal flight then you will have a re-learning period with each flight and your progress will be stunted. So get out often and fly the thermal window for your site and area. Here in Arkansas our peak period is from about 1:30 pm to 4:30 pm with prime time being 2 to 3:30 pm. You should see similar times in your area. Also be sure and watch the weather and check some thermal index sites that will give you some predictive lift indicators so you can better learn which days to concentrate on.

Best of luck in your learning. Hope to see you at cloudbase soon!

Wayne Hobbs