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Thermal Q's - 8/22/2007 6:09:06 PM   
spiral_72



Posts: 511
Joined: 3/7/2007
From: Chesnee, SC, USA
Status: offline 		First, I found an excellent article on RCU for searching thermals:
http://www.rcuniverse.com/forum/m_3900640/anchors_3901498/mpage_1/key_find%252Cthermal/anchor/tm.htm#3901498

Now the questions, I've never caught a thermal. The best I've done was catch some lift over a hot paved road. After reading this article:

I know it varies, but how big should I expect a thermal to be? 25yards? 100yards? a mile?

How tight a circle to fly once/if I find one? 50ft? 500ft? I know it depends in the thermal, but what should I expect?

How low do they start? I mean, after my high-start launch, if I drop below Xft altitude go ahead and come in, cause it's pointless.???

I did read the article thoroghly (SP?) and I found more on the internet with diagrams etc. So I have some indication of what they are supposed to look like and indications of lift. As far as experience or actually seeing it done, I have no idea.

As usual, thanks for the help! Oh, btw, I have a 2m Spirit.

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RE: Thermal Q's - 8/22/2007 7:05:09 PM   
slopemeno



Posts: 448
Joined: 5/24/2003
From: San Francisco, CA, USA
Status: offline 		Its actually *much* easier than youre thinking it is.

Heres what I would do. Make sure your Spirit is in good working order, and youre getting good launches. Hopefully youre flying around noon to 2:00 PM, which is the time of day the thermals are working the most.

A thermal looks like a mushroom cloud. It starts as a bubble of warm air, like a bubble on the bottom of a pot of boiling water. It breaks loose, and begins rolling like a doughnut (inside rising faster than the edge, which can be sinking since its cooling) and climbing. As the thermals reach altitude, they can begin to join up, and suddenly theres lift everywhere. You want to be in the center of the doughnut. 50 feet is probably average size, though closer to the ground they can be quite small.

Heres what it feels like: Youre flying along, and suddenly your plane hangs a right turn with no input. Turn HARD left and go back there, because that was a thermal passing under your left wing. Your plane wants to turn away from lift. Anyway, turn back into the spot where that happend and circle. Remember the thermal is drifting down wind, so follow it.

I seem to have good success off of a high start like this: Launch, come off the high start, and turn 45 degrees cross wind and work across your field. If your plane turns on its own, turn back hard against it and circle.

Now, once youre in one, you'll sometimes notice your plane speed up, and the tailboom rise before the rest of the plane. Turn hard and begin pulling as much up as the plane can take. if you pull too much, you'll see it stall. Stay with the thermal and be ready to stay with it as it drifts down wind, probably behind you. The Spirit is a pretty good penetrator, so you can come back from a spot down wind, but dont get cocky.

You may need to make some subtle adjustments to your circle to stay in the thermal, so momentarily open one side of your circle to follow the thermal, but get right back into it. It pays to be aggressive when staying in lift.

And finally, learn the field you fly. If you know "Oh, that tree line always has something coming off of it" or "That tennis court 100 yards upwind always has a boomer coming off of it" Go for it. Really get in there and ride that lift, and see what you can do with it.

If you havent already, check out the Charles River website regarding the Spirit. They have some good tuning tips that will help you squeeze the last bits of performance out of your Spirit. You may want to put some dark wingtips on the bottom of your wing so its easier to see at altitude.

(in reply to spiral_72)
       Post #: 2

RE: Thermal Q's - 8/22/2007 7:26:43 PM   
BarracudaHockey



Posts: 10993
Joined: 7/13/2003
From: Orange Park, FL, USA
Status: offline 		Trim your plane for hands off flight. Then keep your hands off. You will notice if it gets bumped, turn into the bump. People can thermal with light planes off a hand launch. Thermals start at the ground and spread out as they rise, kind of like an icecream cone. The higher you are the bigger the circle. I've stood my 2m on a wing tip and circled, its just a feel you develop.

Its quite a thrill once you catch a biggun!

As for how how high you can thermal, you need to make sure you have enough room to land safely.

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RE: Thermal Q's - 8/22/2007 11:55:06 PM   
bkdavy



Posts: 1487
Joined: 9/28/2004
From: FrederickMD, USA
Status: offline 		I have a Spirit 2M and its a wonderful thermal flyer. The trick I discovered was to get rid of all the extra weight in the nose. The construction directions have you adding weight in the nose to balance it on the spar. I found that once I removed all that weight, the CG was a little behind the spar, but the plane became much more responsive. I didn't need to worry about the nose dropping quickly, and have more time to see the wings get bumped by thermals.

If the plane does turn on its own, rather than try to force it back, I've found its much more productive to just continue the turn 270 degrees. That will put you almost into the center of whatever lift you experienced. You'll see the plane start to rise when it enters the thermal. Once you start circling, the plane will try to turn out of the thermal, and thats when you want to fight the turn to get back into the thermal. Eventually you'll find an altitude where the plane just doesn't want to come down. Thats when it gets fun.

Brad

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       Post #: 4

RE: Thermal Q's - 8/23/2007 3:18:40 AM   
spiral_72



Posts: 511
Joined: 3/7/2007
From: Chesnee, SC, USA
Status: offline 		From what I read, thermals turn clockwise in the Northern Hemisphere (counter clockwise below the equator). While this in itself is very cool, what direction do I turn in the thermal? Or does it matter? Clockwise with the themal (perhaps considered downwind?) or counterclockwise against the thermal flow (riding into the lift?) ?

I hope to get my Rx in time for this weekend. If not I'm going to burrow the one out of my glow-trainer. I'm trying to learn all I can to have a fighting chance

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RE: Thermal Q's - 8/23/2007 3:21:47 AM   
spiral_72



Posts: 511
Joined: 3/7/2007
From: Chesnee, SC, USA
Status: offline 		Thanks, I'm definately going to make sure the nose is unloaded this time. It's been 12 years since she's been in the air!

I found a bunch of mods (listed above 2nd-3rd post, thank-you), but they will have to come later.

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RE: Thermal Q's - 8/23/2007 3:53:15 AM   
slopemeno



Posts: 448
Joined: 5/24/2003
From: San Francisco, CA, USA
Status: offline 		Thermal rotation is random. Just pick a rotation you're comfortable with and go for it.

If you go to YouTube there should be some handlaunch or discus-launched glider videos on there. Watch how they work light lift low and close to the ground.

< Message edited by slopemeno -- 8/23/2007 3:54:43 AM >

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       Post #: 7

RE: Thermal Q's - 8/23/2007 3:35:50 PM   
sawdust


 

Posts: 194
Joined: 1/7/2003
From: Millstone, WV, USA
Status: offline 		When you take the weight out of the nose of your plane it becomes less stable. Just remember that when you land that you probably will want to come in a little faster so as to avoid a stall. You may want to consider removing the weight a little at a time. Little steps are sometimes are better than big leaps.

Finding thermals is the great challenge. Up higher the thermals are typically wider but weaker. Watch the plane it will tell you when you are in a thermal. Thermals are going to float down wind. So you will need to follow this drifting motion. On days when there a lots of those low hanging puffy clouds moving slowly across the sky there will be thermals.

The more you fly your sailplane the better you get at finding thermals.

Have fun. bob

(in reply to spiral_72)
       Post #: 8

RE: Thermal Q's - 8/23/2007 6:49:32 PM   
bkdavy



Posts: 1487
Joined: 9/28/2004
From: FrederickMD, USA
Status: offline 		For trimming and weighting purposes, I started with the recommended CG. I took the plane to the field, and stuck with hand launches. I would throw the plane into the wind and then try to bring it around full circle. When the plane was nose heavy, this was very difficult. As I continued to remove weight, the circle became easier and easier. I quit removing weight when I could bring the plane around full circle or more, using almost no elevator. I also discovered that as I removed nose weight, the plane became less and less likely to drop the nose as it slows down. Its now weighted such that it will eventually drop the nose, which is essential for a stall recovery, but its going pretty slow when it happens.

I used the full circle criteria based on the logic that I wanted to be able to hook a small thermal close to the ground. Before doing this, If I didn't have a good 50 feet or so of altitude, I would pretty much have to give up hunting thermals. Now I can pretty much fly the length of the field at that height, which gives me that last little chance of keeping it going. The plane also responds much quicker to small thermals, due to the reduced stability.


Brad

(in reply to sawdust)
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RE: Thermal Q's - 8/23/2007 7:25:55 PM   
spiral_72



Posts: 511
Joined: 3/7/2007
From: Chesnee, SC, USA
Status: offline
quote:

ORIGINAL: bkdavy

For trimming and weighting purposes, I started with the recommended CG. I took the plane to the field, and stuck with hand launches. I would throw the plane into the wind and then try to bring it around full circle. When the plane was nose heavy, this was very difficult. As I continued to remove weight, the circle became easier and easier. I quit removing weight when I could bring the plane around full circle or more, using almost no elevator. I also discovered that as I removed nose weight, the plane became less and less likely to drop the nose as it slows down. Its now weighted such that it will eventually drop the nose, which is essential for a stall recovery, but its going pretty slow when it happens.

I used the full circle criteria based on the logic that I wanted to be able to hook a small thermal close to the ground. Before doing this, If I didn't have a good 50 feet or so of altitude, I would pretty much have to give up hunting thermals. Now I can pretty much fly the length of the field at that height, which gives me that last little chance of keeping it going. The plane also responds much quicker to small thermals, due to the reduced stability.

Brad


50 feet!!! I had no idea it'd be that low. Cool.
That sounds like some pretty good advice. I'm saving all this stuff to a file so I can run through it again when I can put the plane in the air. I'm still hoping for this weekend, but my Rx is in Illinois right now. NOOOoo!
As I remember, mine lost altitude faster than that. I know it was nose heavy, my complete inexperience at the time told me to err on the nose heavy side. And boy did I! Now with balance experiences on my trainer the last 2-3 months should help out considerably.

I did look on Youtube and Google video for some thermal action. I've studied several videos, but I can't seem to detect the "symptoms" of a thermal just before they circle. I'm still working at it though. It'd be nice if I knew someone that soared.

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RE: Thermal Q's - 8/23/2007 10:38:41 PM   
bkdavy



Posts: 1487
Joined: 9/28/2004
From: FrederickMD, USA
Status: offline 		The "symptoms" of a thermal are simply a change in the flight of the plane. It could be a wing tip up (or down), or the tail (up or down) or some combination of both. Thats why trimming the plane to fly straight and level hands off is so important.

Once the plane is trimmed and in the air, you let go of it. Let it fly. If it starts to turn on its own (eg banks slightly) then you have either grazed a rising air current with the wing or a sinking air current with the down wing. If you continue the turn 270 degrees, you will either fly into the rising air or out of the sinking air. Both good things to do. As you steady on your final course, watch the plane closely. It will rise or fall. If it rises, you're in lift. Start your circles. If it falls, you're in sink. Keep flying to get out of it.

Once you start circling, keep the circles as tight as you can without stalling. Watch the plane closely as you circle. If it trys to turn opposite your circle, you're probably just outside the thermal, so fight it back into the thermal. Eventually you'll find the boundaries of that thermal. And remember, thermals will move down wind. So let the plane move downwind with it. Its not magic. Its just being attuned to your plane, your field, and the air.

Sometimes to find the rising air, you have to think about the situation. The Manual that comes with the Spirit has some great advice on finding thermals. For example, you normally want to fly up wind to explore new air. But there are times when its worthwile to fly downwind. If air is moving across the ground where you're standing, chances are there is a column of rising air somewhere downwind. Your mission is to find it. Parking lots, plowed fields, cars, and roofs can all be great sources of heat that will drive thermal currents. Depending on where you fly, sailplanes can often get away with flying outside the boundaries, because they don't make any noise. Nobody will even know you're flying there unless they look up.

Look for birds circling. They are great at finding the rising air. I watched a hawk a couple weeks ago launch himself out of a tree and then perform some pretty tight circles about 25 feet off the ground very close to the tree line. In about 2 minutes, he had risen several hundred feet without ever flapping his wings. Wish I'd had my glider that day - I could have hand launched into some real boomers.

I think of thermal soaring like fishing. Its a great reward when you hook the big one. But it takes a lot of casting sometimes to find the right spot.

Brad

(in reply to spiral_72)
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RE: Thermal Q's - 8/24/2007 8:00:09 PM   
spiral_72



Posts: 511
Joined: 3/7/2007
From: Chesnee, SC, USA
Status: offline 		Man! I really appreciate the tons of info and help here. I've learned a lot and it's given me more things and keywords to Google that led to diagrams and more info.

I think I've learned enough to give me a fighting chance this weekend (weather permitting) with my Spirit. I won't have a chance to do some of the mods to the plane by then, but I will later. At least I know what to expect now (I think), and an idea of thermal/circling size should help out greatly.

My Rx didn't come in so I hope to borrow or steal one from somewhere temporarily.

I'll let you know how it goes. Thanks again!

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Wasn't that cool? I meant to do it.

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RE: Thermal Q's - 8/24/2007 10:06:54 PM   
BarracudaHockey



Posts: 10993
Joined: 7/13/2003
From: Orange Park, FL, USA
Status: offline 		Let us know how you make out.

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RE: Thermal Q's - 8/25/2007 12:56:24 AM   
BMatthews



Posts: 9005
Joined: 10/4/2002
From: Burnaby, BC, CANADA
Status: offline 		Best of luck with it. Boy, it's been a while since I wrote the stuff in that link.

As you're quickly learning there's no one right or wrong way for the most part other than learning to "go with the flow" and avoid horsing the model around unless you're in lift. Learning to REALLLY observe the model's actions is also paramount. You need to sharpen your visual perspective of what the model is doing until you can shave with it...

Some folks can walk and soar at the same time. For me I loose too much perspective from the moving background and model so I tend to come off the launch winch or highstart and run out of the way and then settle down and get to work observing what my model is doing.

Outside of that it's all about stick time and practice. Lots of stick time will expose you to all the variations the weather has to offer.

Generally the closer to the ground the smaller and usually weaker the thermals are. But if you can circle tightly enough with good control over the model's speed and gain some height you can progresively open up the turn as you move up further into the fatter portion of the thermal. Again observing the planes climb and sinking will tell you in a hurry if you are circling too open or if you're not centered. Don't be afraid to move the circle around by tightening the turn a little here or opening it up a little there for a portion of the turn to move the center.

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