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Old Sep 13, 2011, 03:34 PM
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I've Hit a Thermal; Now What

Hi all,

I've been at this a while and I'm getting better all the time. But I'm still pretty crappy about catching thermals and capitalizing on them.

I can clearly see when my Taboosh signals a thermal. The nose goes up or down sometimes. More often, the plane veers to the left or right.

So, I launch and the plane is straight and level. Then she veers right. I start a left-hand turn into the thermal. I would expect to see the nose start to climb. Then, I can start a circle and let the plane drift downwind with the thermal.


At least, that's the theory. In practice, I think I'm getting lift, I turn into it, and I fly right back into sink or dead air. Sometimes I hit the thermal and then circle out of it. Sometimes I'm just lost.



There are a ton of launch videos on the site. Everyone focuses on getting better at launching.

Do any of you have videos of your DLG actually *in* a thermal?

I haven't been to a contest or fun-fly yet. So other than theory and a few boomers I've hit, I have no idea what to do after the plane is flying.


Thanks.
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Old Sep 13, 2011, 03:41 PM
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Start turning.

below 30 feet (2 min 49 sec)


This one is good also.

Cyril- JW- SM. Ca. (2 min 33 sec)


You're in GA, so hook-up with Buddy or Walter Roos, they can teach you. I learned by watching Buddy.


Sean
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Old Sep 13, 2011, 03:42 PM
Launch high. Fly low.
United States, CA, Lake Elsinore
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Fly low...
It's the closest thing to being with your plane in a thermal. You'll feel what the plane is flying in and you'll quickly learn what's happening around you AND the plane.
I can't stress this enough.
There are plenty of planes in thermal videos out there. Most of the time you wont see what's happening since the planes are so dang high that the video will teach nothing.

Soar! closely
Jun
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Old Sep 13, 2011, 03:44 PM
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How low are we talking? I get about 110' off my Taboosh on launch. I have about 60 seconds to find a thermal.

How tight are you turning? Are we talking like a 30 bank? 60?
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Old Sep 13, 2011, 03:50 PM
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the bank depends on how tight you need to be. Narrow thermals require tighter turns. wider is better but sometimes the thermal can be quite narrow. I think one always tries to fly as wide a turn as you can afford to while maximizing the available lift.

you tell this by feeling the air and getting input on how the plane reacts.

At least that is what I try to do.
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Old Sep 13, 2011, 04:07 PM
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Xptical:

Thermals come narrow and broad, low and high, rough and smooth, .... You get the picture.

The goal is to find the center, and circle around it. The trouble is, the center is always moving (downwind mainly, but also dancing around, like an eel). So, each circle you make, you also have to judge where the center is, and shift your next circle accordingly.

I always start with a default bank angle of 45 degrees. It's a hold-over of my days as a full-scale soaring pilot. Banking less results in reduced sink (and increased climb), but if the thermal is narrow, well then - you better be willing to adjust. You should fly slow, to reduce turn radius, but with margin over a stall to give power of maneuver.

The nose may rise, but that will only result in a stall. You have to make your thermal turns at a pitch attitude that allows the airplane to fly. The fuselage should present the same attitude relative to the horizon in a circle, as it does when flying straight. This is tough to judge while turning in a circle. The airplane will climb, as long as the rising air is going up, faster than the airplane is descending through it.

If you can fly constant speed circles, at a constant bank angle, that's the basic maneuver skill required to fly in a thermal.

Finding thermals is the fun part. Using them is the hard part, and it's a wrestling match, not an efficiency exercise. Your airplane will (by itself) fly around thermals, if allowed to (and you already know that), and once in a thermal, will leave of its own accord.

Go for it! No one said it would be easy - only fun.

Yours, Greg
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Old Sep 13, 2011, 04:19 PM
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Quote:
Originally Posted by glidermang View Post
Xptical:

Thermals come narrow and broad, low and high, rough and smooth, .... You get the picture.

The goal is to find the center, and circle around it. The trouble is, the center is always moving (downwind mainly, but also dancing around, like an eel). So, each circle you make, you also have to judge where the center is, and shift your next circle accordingly.

I always start with a default bank angle of 45 degrees. It's a hold-over of my days as a full-scale soaring pilot. Banking less results in reduced sink (and increased climb), but if the thermal is narrow, well then - you better be willing to adjust. You should fly slow, to reduce turn radius, but with margin over a stall to give power of maneuver.

The nose may rise, but that will only result in a stall. You have to make your thermal turns at a pitch attitude that allows the airplane to fly. The fuselage should present the same attitude relative to the horizon in a circle, as it does when flying straight. This is tough to judge while turning in a circle. The airplane will climb, as long as the rising air is going up, faster than the airplane is descending through it.

If you can fly constant speed circles, at a constant bank angle, that's the basic maneuver skill required to fly in a thermal.

Finding thermals is the fun part. Using them is the hard part, and it's a wrestling match, not an efficiency exercise. Your airplane will (by itself) fly around thermals, if allowed to (and you already know that), and once in a thermal, will leave of its own accord.

Go for it! No one said it would be easy - only fun.

Yours, Greg
That is what I keep doing! I keep stalling out of lift! I think this may explain it! I'm trying to baby it too much and keep my bank angle at a minimum. I need to bank more. Or at least try it that way and see what results I get!

I'll know in a few hours!
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Old Sep 13, 2011, 05:10 PM
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I like this vid. Strong and rough air.
SALonit (2 min 37 sec)
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Old Sep 13, 2011, 05:43 PM
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Stalling is not really a function of bank angle, but of angle of attack of the wing, plane weight, and airspeed. The simplest way of being in the ballpark during a turn is to watch the angle of the fuselage. See that it stays pretty close to horizontal - the same way it does in straight line level flight. If the nose comes up, use less elevator.

I'm just reinforcing what Greg has already said.

Now, in a turn, we are requiring the wing to generate more lift. It can do so by any combination of flying faster and having more camber.

Usually, we set up our DLGs with either a thermal setting, which applies a few mm more down to the trailing edge, or a mixer that applies elevator->camber to drop the trailing edge a few mm as up elevator is used, or a combination of both (I recommend both). If you are thermalling (turning, really) without using an elevator->camber mix or a thermal camber setting, then your plane has to fly faster in the turns and likely won't climb as well.

If you don't have a thermal setting and don't have elevator->camber mix, try manually dropping the trailing edge - via the stick - a tiny bit and see what happens to your turns.

If the suggestions above for radio setup are new to you, then I suggest reading through and applying the info in the sticky on initial programming of a DLG. It may help a little.

.....

The indicators such as nose rising, plane banking, plane drifting, do not necessarily mean that you have contacted the thermal. They are just indicators of relative air motion. For instance, if your plane banks to the left, and you didn't do it, that means the air around the right wing is rising relative to the air around the left wing. Or at least it means that the majority of the time! However all that air could be sinking, or all that air could be rising!

When you see your plane bank and you didn't command it to do so, then you want to alter the flight path to be in the direction away from where the plane wants to go.

Now, suppose you see the plane drift. That is, it is heading on some track, at a low level, and then the plane changes ground track without really changing its pointing direction in the air. At the low levels we fly, we are near the bottom of the thermals. What is possibly happening here is the plane is being pushed away from sink (it is spashing down on one side) or the plane is being sucked towards lift (thermal sucking up available air like a vacuum cleaner held hear the ground). In this case, you want to go to the direction of the drift.

Now, suppose you see the plane's nose rise and you didn't command it to happen. That could mean one of several things.

First possibility is the plane has hit some lift. The front of the plane hits it before the back gets there, so the front gets a lift before the back does. So, the plane pitches up a little. When this happens, watch to see if it starts to fall off to one side or the other a little bit. Start your turn in the direction away from where it headed. But don't wait more than a couple seconds to make up your mind! If it doesn't start to turn slightly (in the wrong direction) on its own, then pick a direction and turn. Which direction? The turn is slightly more efficient, very slightly, with the throwing blade on the inside of the turn. But practice each way... Once you have a turn established, watch that first turn to see if the plane maintained altitude or climbed. If it did, keep turning and try to refine the turn location for better climb. If it didn't climb, then you were fooled by the air... so go do something else!

Second possibility is the plane hit a local gust and the plane is set up to be pitch stable. A statically pitch stable airplane will pitch up if it is flying too fast. Flying too fast is what happens when the plane hits a gust head-on! So windy gusty turbulent conditions are tricker for finding and flying lift. Experience helps to determine whether what you hit was rising air or air that just happened to bump up your plane's airspeed.

Third possibility is the plane hit a local lull (opposite a gust) and the plane is set up to be slightly pitch unstable. I recommend not having the CG that far back as flying gets rather trickier. So assuming your plane is set up so it flies itself hands-off a good portion of the time, we can neglect this possibility.

The ideal scenario may go something like this:

You see your plane bank a little to the right. So you gently persuade your plane to go to the left while maintaining level flight. It still wants to curve off to the right - resisting you a little. So you start a turn to the left. On one part of the turn, the plane gets tossed up a little and thrown into a bank. You have hit a CORE! This is a little column of rapidly rising air. These are golden! Now the job is to put as much of your plane's turn in the core as possible, and to keep it that way. A core will likely try to toss you out.

Some thermals are going to have defined cores. Some are just going to be regions of soft lift. Some are going to have multiple cores. Often the cores move around, disappear even, and re-appear somewhere nearby. When you lose a core, open up the circle larger and read the plane. Try to find another core, or at least center better in the lift you have available.

Thermals can keep your plane up, and even make it climb. Cores are like fast elevators. You can sky quickly if you get into and maintain contact with a core!

Thermals drift with the wind, usually, but not always at windspeed. Actually, sometimes thermals do whatever they want to do and not what you expect them to do. So just because you are in one doesn't mean it is time to get complacant. One must maintain vigilance to get the best out of lift.

Many times there is more than one thermal in the immediate area. In such cases, usually one will win and the other will lose. In between the two is usually sink. So if you are circling in lift and planes are circling in lift a little bit away, watch out. If your's starts to do not as well, then you may need to make a run for it to catch the other thermal.

In general, if you hit sink, go faster and be somewhere else. Faster is using speed mode. If you hit lift, go slower and use it. That may be cruise or thermal (float) mode.

Gerald
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Old Sep 13, 2011, 05:56 PM
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Here is my flight from this afternoon. The wind was fairly calm and there were some nice thermals. I really couldn't capitalize on them properly. This is one of the nicer thermals I hit. I had to bail because it was RIGHT over my head and I couldn't see the attitude of the Taboosh.

Still, I can see how sloppy my altitude management is. I'm all over the place. At one point, losing like 12' in a matter of seconds.
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Old Sep 13, 2011, 09:47 PM
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Good info! Thanks Gerald!!!

BTW, is speed mode also launch mode?
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Old Sep 13, 2011, 10:22 PM
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Madd:

For many folks (myself included, as I am not so technically competent), speed mode and launch mode are the same. The Blaster 3, however, specifies camber for (1) launch; (2) speed; (3) cruise; and (4) thermal.

The big difference between speed and launch is that in launch, you most likely want the airplane to fly at a condition of zero lift (the same as minimum drag). In speed mode, you want some stability while flying pretty darn fast.

Depends on your radio capabilities and what works best for your airplane. I've been happy with three modes, but I'm not exactly planning for next year's world championship.

Yours, Greg
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Old Sep 13, 2011, 10:39 PM
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Quote:
Originally Posted by glidermang View Post
Madd:

For many folks (myself included, as I am not so technically competent), speed mode and launch mode are the same. The Blaster 3, however, specifies camber for (1) launch; (2) speed; (3) cruise; and (4) thermal.

The big difference between speed and launch is that in launch, you most likely want the airplane to fly at a condition of zero lift (the same as minimum drag). In speed mode, you want some stability while flying pretty darn fast.

Depends on your radio capabilities and what works best for your airplane. I've been happy with three modes, but I'm not exactly planning for next year's world championship.

Yours, Greg

Cool, thanks! Yeah, that will work for me too. I don't see myself competing in this (at least officially). But I still want to become proficient and spec the mofo out.
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Old Sep 13, 2011, 11:25 PM
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I'm not going to the World's, but I compete literally every chance I get. I'm traveling to Utah this weekend for my third Blue Skies of the year, and there will be another one in Arizona in November, and a local contest here in October, plus a Beat-the-Heat in Tucson and maybe another weekend special in Albuquerque.

It is cool fun, and you will not believe how much you can learn, until you get yourself to a contest, and walk out on that field with everyone else! There is absolutely no better place to learn than at a DLG contest.

Yours, Greg
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Old Sep 14, 2011, 11:38 AM
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After yesterday, I decided to completely re-program my DLG. I deleted everything. Removed all the servo horns and such. Then started re-building.

I was never happy with the rudder and elevator linkages, so those were the main target. I now have plenty of throw on those.

I set up the wings according to Gerald's guide. At least I think I did. I used subtrim to get the flaps at the same deflection when the flap stick was centered. I used end-points to make sure when they are up and down, they have the same deflection. I used +30% differential to get the ailerons to deflect 26mm up and down.

I did some test flights today with all the flight modes being equal. I used the subtrim menu to set up my elevator deflection for best glide.

I didn't need any rudder or aileron subtrims.


I also didn't set up speed (although the settings now will become speed mode), fast thermal, or slow thermal modes.


Even without a real thermal mode, I could see the thermals and even had a few longish flights. I used one thermal to get altitude so I could do a dive test. I'm happy with the CG and elevator.

I then programmed a few clicks of up-trim into launch mode and tested throwing up at maybe 15~20 and letting the elevator trim rotate her to almost vertical. I clicked out of launch and into speed to continue the climb. I also practiced leveling out before I stalled at the top.


I'll work on the slow and fast thermal modes later this week. It being a Taboo wing, I know, more or less, where these need to be; 3mm down and 6mm down.
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