Field Trip in the Sky
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“Hi I’m Ian Worley. I’ve been flying since I was in high school. I sold strawberries to get my pilot’s license. But I’m also a teacher at the University of Vermont. I teach about the out of doors, landscapes, living things and geology, and I teach about environmental issues.

“And one of the things I do is I take my students on aerial field trips, because we can see things from the sky that we can’t see so well from the ground. But more excitingly, we can have a feel of the sky and learn its shape, what’s going on in the air-- because the air is sometime invisible and we can feel it with the airplane.

“Today, we’re off looking for thermals, those rising columns of air that take gliders and hawks and butterflies to higher heights so they can glide to the next thermal and find their way south during migration.”

Air traffic control clears the plane for take off…

“You can keep that shoulder harness loose and comfortable,” Dr. Worley told me as we prepared to leave, “but make it nice and tight in case we need to land in the trees.”

Once airborne, Dr. Worley searches for signs of a thermal...

“I see a little thermal possibility here, with a cloud above it to my left, up over a swamp called Fairfield Swamp. So we’re going to fly to it and see if we can get an upward rise of air, which we’ll feel as a bump. And if it’s a really good bump we’ll feel it in the seat of our pants.”

The plane bumps.

“Bump! Just like that!

“Now if that cloud were a thundercloud, if there were rain coming down and lightening, we would be flying the opposite direction, not toward it, away from the cloud, because those are rather violent things in the sky and not good for an airplane of this kind.

FlightThermalWorley045 FlightThermalWorley047 FlightThermalWorley048

Flying closer and closer to the cumulous cloud, expecting the plane to bump, jump and wiggle in the rising air.

“But this is a very benign cloud and to look at the cloud it’s cottony, and because it’s looking like cotton--not cauliflower--that means that it’s evaporating. So on the bottom new, moist air is being added and on the top it’s evaporating, so this cloud is going to stay about this size for awhile.

“Now all the water that’s in a cloud that you see-- it’s water --so it weighs something. So you can look at clouds and say, Huh, if I weighed the water that I can see, I wonder how many elephants it would be equal to. Well I’ve done some of that knowing what other people’s research is, and we’re going to about a 50-80 elephant cloud up ahead here. And if you’ve been watching this cloud you’ll notice it’s evaporating, but another one to its left is forming. See, now there’s our original cloud breaking up now, but off to the left there’s a new one forming, and a couple others to the right.

“Aha! Right ahead of us we have birds circling—hawks--between us and the cloud. And that’s the best indication of a thermal.”

The plane zips past 5-8 hawks that were rising in the thermal.

“And we just are going to go through it right now. And they were following it and turned off to our right. And because we were flying at almost 100 mph and are not a glider, we were not able to join them. But if we were in a glider, we could join that thermal and rise up with them. They were in a stationary column that actually might be drifting a bit because we do have the ever so slightest wind today, and the column would drift with them.

“Now sometimes the columns are not columns they are bubbles. They break free from their source. We just had a little bump right here, it may not show up in the camera but we can feel it in the airplane. So sometimes a bubble of heated air goes up. And once that’s exhausted, there’s no more rising air right there.

“So what we’re going to do is we’re going to fly under this first cloud, and we’re already getting a little wiggly air up here. This is not a day of high drama, so we may or may not have a noticeable bump when we go under this cloud. But we’ll give it a try. And then we’ll turn and go under the one to the left and see if that’s an area of rising air.

“So definitely now the airplane is wiggling a little bit, so we’re definitely in rising air…Here comes the cloud…and we are kind of hopping around a little bit here. Looking at the cloud we don’t notice it but looking at the horizon we notice it.

NO BIG DEAL of a thermal..

“OK, so we went under that and it was NO BIG DEAL of a thermal. And I’m going to skinny around here and try this one that’s growing right now, and see if we can find a bump.

"And now we’re definitely climbing. Right here it says we’re going up at 500 feet a minute. Look at the altimeter, it’s moving upward, and it says 600 feet a minute and we’ll probably come out of this and well quit going up…and we’re back to stable air.

Riding Through a Thermal
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Rising 500 feet per minute... Gaining altitude... Then back in stable air

“Well, it wasn’t a bump but it was certainly a stable climb. How many feet did we go up? We went up for about 30 seconds at 500 feet/minute so we went up about 250-300 feet as an airplane passing through it. Now those hawks, the reason they were circling, was so they could stay in it. And that’s what gliders do.

“So it looks like today if we are a bird or a butterfly or something else that wants to take advantage of thermals, we’ll have light thermals in the ground below us which is some open fields, some wooded cover, and where the woods are it heats up more.

"So we’d be better off to go over near the ridges, because we definitely see clouds over the ridges….”

And off we flew, above Vermont’s tallest peak and beneath the cumulous clouds, in search of a bumpy ride in a column of rising air…

Special thanks to Dr. Ian Worley for the invitation to fly, for his colorful commentary and his skillful flying, and especially for “watching for a safe place to land” throughout the flight — but never needing it.



Dr. Ian Worley
Professor and Pilot
Looking for a Thermal
Heading for the Cloud
Rising in the Thermal





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