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Old Jun 01, 2015, 09:35 AM
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On catching thermals

Catching a thermal is magical. Thrilling. Addictive. And it's an art.

I figure a Thermal forum could use a thread exploring the art of hunting - and catching - thermals. There's lot's of information all over RCG and other forums, but we could condense some of the more pertinent points - and questions - here.

(I am adressing this as a beginner with little over a year of flying a 40" balsa built DLG. Started with 24m launches and get the occasional 34m now. I distinctly remember my first 3 min flight, then reaching 200m next. I found out my Spinnin Birdy is really tiny at 480m, and with a pb of 23 min. I now want to crack the half hour. And I am 60 years old.)

I hope some of the more experienced guys will contribute more substantial pointers that will help beginners up their chances to see their plane rise higher and higher. The three things that really made the difference for me are

- Get that CG dialed in to feel just right
When nose heavy enough, my DLG will run on rails. Plow through the air like a truck. For 45 seconds. Wouldn't notice a thermal if it hit it head on. I taped some flattened lead to the fuse to move that CG back (two down clicks on elevator trim), and back some more, and some more - until my plane needed constant hands on control to keep it in the air. Then I moved CG back forward just a bit, and that feels right. Now it flies connected to the surrounding air, shows me what's going on up there. (Your factory cg will always be on the safe side - read 'run on rails'. If you are looking for thermals, this is not what you want.)

- Take your hand off the stick(s)
As a beginner, I have one primary goal: Get my plane back down in one piece. So I had both hands on the wheel and drove it through the air. WRONG. It took a conscious effort for me to launch my plane - and just leave it alone. Watch what it does. Give it time to show me what is going on up there. And with the cg just right, it started to show me plenty. And I started to gently coax it towards whatever it wanted to shy away from. That's how I caught my first thermal.

- Elevator is not about up/down
I always thought the elevator makes a plane fly higher or lower. It really helped me to understand that the elevator on my plane is all about speed. I found that my plane has a certain speed it "likes" to fly. And catching the thermal meant keeping my plane in its favorite speed range through bumps and turns. Circle after circle. Higher and higher. Magic.

Anyway, tons more to be said. Let's see what happens - and happy flying.

Thomas
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Old Jun 01, 2015, 09:42 AM
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This sort of prompted me to actually start this thread:

http://www.rcgroups.com/forums/showthread.php?t=2425429

Fun read - couldn't agree more.
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Old Jun 01, 2015, 10:01 AM
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Thomas,

"Catching a thermal is magical. Thrilling. Addictive. And it's an art. "

Your opening line is as accurate as it can be. I have been catching thermals since 1968, started with a magazine construction article plan with a .049 gas engine on the nose. I'm still addicted

Ray
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Old Jun 01, 2015, 08:36 PM
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Once you are listening to the airplane (by staying off the sticks) you're ready for the first rule of thumb:

Whatever the airplane wants to do is wrong.

Lift is strongest in the center, so the tip closest to it gets lifted more than the one farther from it. That makes the airplane turn away from the lift- reverse the turn.

Same goes for the nose and the tail-- the tail will rise and the airplane will scoot away from lift. Turn around and go back.

Approaching lift, the nose will rise and the airplane will balk like a horse. Lean forward on the stick and press your way in to it.

The better the lift, the more violent each of the above reactions will be.

Oh, and enjoy the magic!
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Old Jun 02, 2015, 02:45 AM
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Originally Posted by Ray Hayes View Post
I have been catching thermals since 1968, started with a magazine construction article plan with a .049 gas engine on the nose. I'm still addicted.
Hi Ray,
Thanks for stopping by! I think I built my first free flight kit in 1968 - Graupner's "Der kleine Uhu". My idea to increase flight times then was to climb on something high to chuck it from.

Would you have a bit of advice to beginners with a decent enough plane to experience the magic of catching their first thermal?
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Old Jun 02, 2015, 02:51 AM
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... the first rule of thumb:

Whatever the airplane wants to do is wrong.
+1. (I love her anyway).

I find it really hard to tell the difference between a bump in the air and an indicator of lift. Any thoughts?
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Old Jun 02, 2015, 03:54 AM
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Weather forecast

If Thursday isn't a thermal day I don't know what is. Light easterly winds up to 6 mph, temp going from 3 to 23*C, clear skies. Just gotta be great.
I think I will have a 3+ hour appointment with my DLG starting at about 10 a.m.
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Old Jun 02, 2015, 10:38 AM
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I find it really hard to tell the difference between a bump in the air and an indicator of lift. Any thoughts?
Me, too. The short obvious answer is that a bump in the air *is* lift-- but that doesn't necessarily mean its usable. Your ability to work weak or tightly bounded small bubbles depends on your ability to fly smooth, efficient turns that don't waste energy.

My general practise is to circle back and revisit most bumps. If I can find it twice, and I don't lose more altitude turning back to it than I gain when I hit it, then its all good!
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Old Jun 02, 2015, 10:47 AM
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That said, the "stick thermal" is never really lift, and can be harder to spot. Stick thermals are a result of some control transient, like pulling up elevator. (Duh! Up elevator's not a thermal!)

But turning from crosswind to upwind can cause an altitude change as well, as can any speed change, and these won't look like you pulled back on the stick.

What you're looking for is a change in the status quo- put the airplane in a steady state, stop talking to it, and listen for something to change. As you get practise and become familiar with the airplane, you'll be able to hear it better because you'll start to see the difference between what it *is* doing and what it *ought to be* doing.
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Old Jun 02, 2015, 10:55 AM
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But turning from crosswind to upwind can cause an altitude change as well
And that's when the arguing started.
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Old Jun 02, 2015, 11:52 AM
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And remember to slow the airplane down when in lift ... Circle as slowly and flatly as possible while staying coordinated , however many bubbles start smaller at lower altitudes and expand as they rise thus making your thermal larger on the way up... If you notice excessive turbulence without climbing anymore the thermal has become ratty at the top and it's time to move on.
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Old Jun 02, 2015, 01:40 PM
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And that's when the arguing started.
Experience is what it is. I suspect that most such arguments proceed from differing definitions and understanding of what "crosswind" means.

If the airplane is drifting along with the wind so that it's airspeed is completely independent of the wind speed, it's not really "moving crosswind" is it?

In any case, I'm talking about an airspeed change that is induced by an attitude change (or vice versa), people can call it whatever they want. <shrug>

The important thing is to understand when it's your fault, when it's the prevailing wind's fault, and when it's LIFT's fault.
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Old Jun 02, 2015, 02:21 PM
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I don't disagree with the points you're making, just couldn't help myself.

As was mentioned earlier, the higher up you are, the wider the thermal is likely to be. So if you're up high and you get a little bump, give it a couple of seconds before making your turn. You might find the best part is still in front of you a bit.

Also, sometimes you get a bump but can't seem to thermal in it, but if you go back through the same place you hit the same bump again. Sometimes you get a wave from something on the ground, a treeline or maybe just the geography. I once timed a contest flight for Cal Posthuma on a fairly windy day where he basically parked his sailplane in a wave using flaps to reduce his groundspeed to zero. He worked it left and right, forwards and backwards, just keeping it in the wave. He made his time (8 to 10 minutes, I can't remember for sure) and landed without ever doing a thermal turn.
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Old Jun 02, 2015, 02:38 PM
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Wave lift is the best and most fun lift you can find in a FS... Smooth and at 1k a minute it's like riding an elevator to A airspace with minimal ground speed . However associated rotors will make you work and is some of the most turbulent air you'll find.
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Old Jun 02, 2015, 02:56 PM
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On Catching Thermals

Like describing the working of this Perpetual Water Wheel

A little Black Magic, best not explained

Just go fly

whacker
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