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May 27, 2003, 04:50 PM
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How Do You Catch A Thermal??


Hello,
How do you catch a thermal? Also, how do you know where they reside. How can you tell if you are in a thermal, will u just start to rise? Lastly, can a GWS Slowstick thermal? -Patrick
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May 27, 2003, 04:55 PM
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Fast-Forward's Avatar

So you want to know about thermals


Yes, a Slow Stick can thermal.

Here is a guide to learning about soaring click here and another Click here

A thermal is warm rising air which (hopefully) will carry your model to a great height. There has always been some debate as to the actual shape of thermals. Thermals are said to be either columns of warm rising air, doughnut shaped bubbles and some fliers perceive them to be large bubbles of warm air which form at ground level then break away to float skywards. It may be that thermals are large columns of warm air with a cool (downward flowing) core, centring on a thermal is a common phenomenon, if a free-flight model centres on a thermal the result is a downward almost vertical spiral which is often terminal !

Whatever shape thermals are - you will want your model to be in one! There are many variables that are involved in producing thermals ie; air pressure / cloud formations / sun intensity / wind strength / the surrounding terrain, the list goes on !

I must point out that thermal picking is not an exact science and many an experienced flier has been seen with head in hands as his models wallows slowly earthwards in a patch of 'sink'. Even experienced fliers get it wrong from time to time.

We will assume for the sake argument that thermals are columns of rising air. As this column of warm air rises, cooler air will precede it and a cool air will rush in the fill the space previously occupied by the rising warm air.

There are strong thermals, weak thermals and patches of air that give the appearance of thermals but collapse moments after launch. We can't see thermals, so we need some means of detecting them and avoiding the down drafts.

Natures little helpers

Nature can provide evidence of thermals. Small feathers, floating seeds and insects can all give clues as to when thermals are present. Look for these items floating towards you, if they are floating upwards then you may be sure that they are in warm rising air. Also look for circling birds which are hunting insects they also give away the presence of thermals.

Indicators
Wind is your friend - keeping in mind that a thermal pulls air away from you. If there is a breeze, or a change to a steady wind, expect to find that it is produced by an updraft (a thermal) downwind from the breeze or change in wind velocity. In other words, launch with your back to the wind.
If you see small puffs of cloud, head towards them. These are produced by thermals meeting the cold air "ceiling". Its warm moist air loses energy, condenses, and becomes visible cloud.

Trees - yes trees. One evening, near sundown, with a row of trees at the edge of the field facing into the sun - I noticed that the leaves on the trees would flutter for a couple of minutes, about every 8 minutes or so. So when I saw the leaves on the trees start moving, I flew my plane over the trees and sure enough, they were giving off heat (the plane started to rise). Apparently they went through a cycle where the sun (almost perpendicular to the trees) would heat them up enough that the hot air rising through the leaves drew surronding cooler air into the tree, also causing the leaves to visibly flutter, until the leaves were cooled off. The visual indicator was important here as I could not always feel the breeze from where I was standing.

Birds. If you see sailbirds - such as hawks, eagles, buzzards etc., and they aren't flapping their wings and they aren't descending - go fly with them. Sometimes, when you are in a good thermal, these birds will appear out of nowhere to see what you are doing.
Last edited by Fast-Forward; May 27, 2003 at 05:09 PM.
May 27, 2003, 05:39 PM
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Cant you get outta the Downward thermal, the "sink"?

Also, like, how do you stay in a thermal?? Lastly, how big are they usually?
Last edited by putt_13; May 27, 2003 at 05:41 PM.
May 27, 2003, 05:49 PM
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Alfred's Avatar
You have to first stalk it carefully. Be quiet and don't let it catch on as to what you are up to. Use a good brand thermal net and make sure that the container to store it in is a aproved one. Now, first you have to.....................

You will slowly get the hang of it. One of the things that you want to do is to trim the SS, so that it will fly hands off. When done cruise aroung the sky and watch it carefully. Some times you might see a wing tip rise, this normally indicates warm air rising. Test by circling the plane in that direction over that spot again.

It's alot more complicated then that, but it's a start.
May 27, 2003, 05:55 PM
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Ok,
I was hoping it was something like that second description...the wingtip one, though I did laugh a the net one. I knew some joker would post one..LOL...Anyway, I was just flying the SS, and I was confused as to when I would notice a thermal. Like, can a SS thermal without any power, or will I still need to run the motor? Thanx -Patrick
May 27, 2003, 06:06 PM
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Hello,
Back from another flight. I think I mighta caught a thermal, or else its just wishful thinking. I have my slow stick, with an 8 cell 600 AE pack, and a 5.44 oz digital camera up, and it was climbing on 3/4 throttle. I then glided down for about 5 minutes. I think there mighta been some slight thermals, becuase usually the airplane comes down sorta fast. Who knows. -Patrick
May 27, 2003, 06:10 PM
I take a big box with me when I go sailing. When there is a good thermal, I open the box and fill it with hot air. Later if I can't find a thermal, I fly low and over the box, which I open quickly, and that is usually good for another five feet of altitude. It takes a little experience and a lot of hot air.

Jerry
May 27, 2003, 06:30 PM
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Hrm....I hope to catch one of those buggers one day. Does the SS just rise all by itself, or does it need some throttle to raise it. -Patrick
May 27, 2003, 06:56 PM
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Alfred's Avatar
If it is properly trimmed, it should thermal. I had a friend thermal a Multiplex Piper Cub once. I have thermaled a Twin Star before. Didn't get much height gain, but it didn't come down.
May 27, 2003, 07:17 PM
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WOW, caught some major thermals over my house. The roof is totally black, so it get REALLY HOT. Well, the Slow Stick would just float. I could stay in the air FOREVER. Over the house, it wouldnt sink, but sorta stay level, or occasionally rise...COOL STUFF. -Patrick
May 27, 2003, 07:24 PM
Motor Maniac
I was going to answer something like Alfred, but he beat me to it.

One thing you can look for is a surface on the ground that will heat faster than the surrounding area. Bare dirt heats faster than grass, blacktop faster than dirt, roofs faster than dirt, etc. These are good places to fly over and see if the plane reacts at all. It won't rocket up in the air usually, but may just tip a wing a bit. Circle back around to the same spot and see if you can get some lift.

HLG's are great for learning to thermal. They don't have a motor, so they sink if there is no lift. You learn a lot faster with a glider than you will with the SS, but your arm may fall off launching the glider repeatedly.
May 27, 2003, 07:27 PM
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putt_13's Avatar
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I am making a HLG, and HIGH-Starting it. Should be interesting...Also, could you really hand lauch an HLG high enough to catch enough lift to get it up above the trees, houses, etc.
May 27, 2003, 07:45 PM
Alt + 24 = ↑ & Alt + 25 = ↓
Miami Mike's Avatar
Quote:
Originally posted by putt_13
...could you really hand lauch an HLG high enough to catch enough lift to get it up above the trees, houses, etc.
You need more ambition than that! The object is to "speck it out".
May 27, 2003, 08:10 PM
Soaring Circuits
rcbrust's Avatar
Quote:
Originally posted by putt_13
...Also, could you really hand lauch an HLG high enough to catch enough lift to get it up above the trees, houses, etc.
When my buddy and I go HLG soaring, we don't consider it a good day unless we speck out a couple times at least. My personal record with my XP-3 is 1700 feet.

Randy
May 27, 2003, 08:12 PM
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putt_13's Avatar
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Thats with a hand lauch. I guess I am under-estimating the power of your throws. What happens when you dont get any lift.....bet there are some LONG runs to retrieve down airplanes. -Patrick


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