Switching Directions in a Thermal
One of the most common un-centering techniques that students demonstrate to me is switching directions in a thermal. It always happens, a student is not completely centered, the ADHD kicks-in, or something kicks-in and they decide to switch directions. I make sure to look around really well and let them fly right out of the thermal, generally not finding it again. Makes for a good debrief.
Typically when you switch directions you do not just start rotating the other direction. You have to roll into the other turn which looks more like a figure 8. The problem is you were circling in the rising column of air and now are next to it, you know where the sink is.
Sometimes this reversing turn can pay-off. Normally I find it is useful when you are really just not centered, like a quarter in the turn and rest in the sink. This might be enough of a change to become centered. However I find other centering techniques more reliable like a 270.
The first time I had successfully done this was with George Lee at his camp. The reasoning for the change in direction was because the thermal was not producing the climb rate we were expecting. This is also impressive when you are trying to do this in an Open Class sailplane and the roll rate is based on a calendar. But it just felt a little off and we discussed it and tried switching and sure enough we got a better climb going the other way.
Occasionally you will notice that a thermal is just not producing the climb rate that you would expect from what you felt when you first entered. The thermal was most likely rotating and you are going the wrong direction (I don't know what the wrong direction is, but am hoping someone smart will email me and I can share it next week).
When you roll out and try and re-enter the thermal you need to think about where you just were so you need to think more for a 270 degree turn first to move back into your old location. It will only be a few seconds and with the help of a moving map GPS it is very possible to find the thermal again. However looking inside at the moving map could be fatal with other gliders out there.
I am sure you had your primary instructor say don't switch directions. Because that is what I tell my students. Normally it results in loosing the thermal as stated above. Another issue is it wrecks havoc on the gliders about to join with you. Imagine you are pulling up and rolling in behind someone as they start going the opposite direction. Typically when pilots rolls out of the thermal they roll straight, predictable, also the fastest way away from the chaos. As the exiting glider rolls out it is easy to slide into their place. But when you switch directions the merging glider could be in for a surprise.
Switching directions is something I very rarely do. Normally it is not as efficient for re-centering, especially because it is easier to loose the thermal. It can be unsafe and confusing for the other gliders around. The only time it benefits is when a little voice whispers in your ear 'it should be stronger, try the other way'..
Garret Willat holds a flight instructor rating with over 8000 hours in sailplanes. His parents have owned Sky Sailing Inc. since 1979. He started instructing the day after his 18th birthday. Since then, Garret has represented the US Junior team in 2003 and 2005. He graduated from Embry-Riddle with a bachelor's degree in Professional Aeronautics. Garret represented the US Open Class team in 2008 and 2010 and the Club Class team in 2014. Garret has won 3 US National Championships.
