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Old Feb 03, 2012, 02:58 PM
Chuck 'Em and Chase 'Em
Fly2High's Avatar
United States, NY, Plainview
Joined Aug 2005
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How do you tell the difference between turbulence and lift/sink?

I will be a little naive but what tells you that the air that just disturbed a plane is actually lift/sink or turbulence?

I would suspect that both sinking or lifting air will cause a plane to pitch yaw and/ roll.

Wouldn't flying through turbulence do the same?

Is the only way to know is to take a few turns in it?

Is the magnitude of the disturbance and measure of whether it is turbulence or lift/sink?

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Old Feb 03, 2012, 03:15 PM
SB-28 UK Display Pilot
GeeW's Avatar
Joined Jul 2001
2,486 Posts
Well yes and no really!
One of the by products of lift being generated is turbulence although you can can turbulence on its own.

On the edge of lift is often turbulence but often it has a consistence to it like a rhythm much like driving over cobblestones slowly. This is often the mixing of the "warm" air in the lift and the "cold" sinking air.
Unfortunately the band of turbulent air between the sinking and still air and the band between lift and still air is often very similar, but if you can correct your flight path to always go to the better air then you'll be doing better than most.

Pure turbulence is often nearer to random in the planes movement but often is predictable, but by no means always as to its location.
Not a lot of help really.......

Oh I have already fitted my flamesuit and other protective gear!
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Old Feb 03, 2012, 08:26 PM
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Jacksonville, FL 32244
Joined Apr 2004
165 Posts
I believe what determines how much and where you encounter sink/lift/turbulence will be determined primarily by where you fly (such as over flat land, in mountainous or in cliff areas), and weather factors (hot/cold/ temperature, wind direction and speed, cloud types, the season of the year, etc.).

I've been in every US state (except Hawaii), and I've observed over several decades literally thousands of turkey vultures (buzzards) as they've flown in just about every imaginable weather condition. I've seen them encounter sudden updrafts and downdrafts, and as they've flown what I call the warmer and cooler "highways in the sky" as they've searched for and found thermals. I've learned much from them. In my opinion they are the true masters of the sky.

Having said this, I've learned a great deal observing them, and from flying all kinds of RC sailplanes for decades. With these experiences I humbly offer the following, which should answer your questions:

1. As you search for thermals your sailplane will almost always be in sink, sometimes barely visible, whereas at other times quite obvious. It doesn't
matter If you are in front of or behind a thermal, or if you are flying toward or away from it. The fact is, if you are not in lift, you are almost always in

2. Over flat land what makes the difference of the size of a thermal at any altitude will be its distance from the ground. This means the higher from the
ground you penetrate a thermal, the bigger the thermal will be. By "bigger" I don't mean how strong the lift, but rather how wide from one side the
thermal to the other side of it.

3. At what point you encounter a thermal will determine your sailplane's reaction to it.

A. If you fly into a thermal and both right and left wings are immediately in lift, then the rudder/elevator portion (the tail) of the sailplane will rise first.
I recommend you continue flying straight until you exit the thermal, then turn 180 degrees either to the right or to the left to get back in it. Let's
say you think it took you 10 seconds to fly through the thermal. When you enter back into it, fly for 6 or 7 seconds, then start flying in a circle --
because you've probably found the center.

B. If however you encounter lift with the right wing, then the right wing will rise, giving you the appearance your sailplane is turning left. If only the
left wing enters the thermal, then your sailplane will appear to turn to the right. This is because you have penetrated the outer edge of the
thermal. What to do? If the sailplane appears to want to turn to the left, TURN RIGHT! If the sailplane appears to turn to the right, TURN LEFT!
Then follow the instructions in A. above.

Think of thermals as if they were mini-tornadoes, because that's what they are. They can be in strength from very weak to very strong. They can also be very small or very large.

You may also encounter what is referred to as a "bubble" of hot air ascending skyward. These are not true thermals, and it is difficult to take advantage of them. But centering your sailplane in one and keeping it there (provided the bubble is large enough) can give you good altitude as if it was a thermal.

Now about turbulence -- your sailplane will be bounced around in unpredictable fashion, NEVER giving you the kinds of steady and reliable indicators of lift described above.

These have been my observations and experiences. I hope they help.

DC -- Jacksonville, Florida
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Old Feb 03, 2012, 09:02 PM
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United States, OR, Corvallis
Joined Jan 2010
956 Posts
Plain 'ol turbulance vs Thermals....

Now "THAT" is a great question, one that I still don't have a solid answer for but I'll give you my 2 Cents:

My dinky 37" wood polyhedral rud/elev plane bobs around a LOT more than my other planes since it's small and light and thus, it's harder to read. You always know when/where the air is unstable, just not always able to tell what it's doing exactly. But when it goes up, it tends to do so quickly, almost like a plastic bag.

My 2M and heavy wood Easy Eagle rud/elev/flap plane is a lot steadier and thus easier to read.

What I do is I like to look around wherever I'm flying and notice as many obstacle features in, on, or surrounding where I'm flying and think about the dominant air movement direction and where the rotors may be coming off of the leeward side of one row of trees, or conversely "slope lift" on the windward side of trees, slope in the landscape, dark areas warming more(bare dirt, asphalt, rocky areas, a thick grove of leafless trees in the winter creating a dead-air warming spot, etc).

In short, I think about how the surroundings "should" be affecting the air and take notes all the time if I find something different happening and try to piece it all together.

With all that In mind, I try to stay out of the likely rotor or other landscape induced turbulance areas and then I pretty much then do the next "standard" things such as fly and when my plane gets a wingtip bounced up, I counter-turn into that direction and give it a 360 circle and see what happens, try to "read" the plane and try to adjust my plane from there, or if the nose suddenly goes down and the tail up, I try to quickly turn one direction then the opposite to try to re-enter a thermal core. If the nose goes up, I try to put the nose down, gain some speed and quickly level off and go into a turn and see if I just flew through some downwash and try to get into a thermal core. Again, if it doesn't start maintaining altitude or gaining altitude within one 360 circle, I fly off and go look elsewhere for lift and assume I just hit something messy or I just totally misread and mismanuevered a thermal. I haven't gotten that whole thing figured out yet.

Now, just to add confusion- when "tree-surfing", there seems to always be a triangle shaped "wedge of confusion" tubulance below the "slope lift". Once you're in the "wedge", the best thing is to try to fly into the wind nose down and get out and work your way back into the lift layer if possible, or just come in for landing which seems to be the main outcome for me.

Also, Once in a rare, rare while when(usually mid to late spring) conditions are just right at the main place where I fly with an Eastern and Western long tree line on each side(a BIG field of about 12+ soccer fields connected -6 on each side with a bike path in the middle going north/south), the wind will blow steadily at just the right speed out of the West, make a big rotor, and a downslope draft, then bounce off the ground and go up and make a Secondary Rotor in the middle of the field(usually near and parallel to the bike path). 3 times in the past I caught this situation and was able to soar north and south on the uplifting side of this Secondary Rotar making a "standing wave" on it's Western side. It's pretty tricky and really cool to experience, but I haven't been able to ride it as long as actual thermals because either it fizzles-out or, just as likely (or more so) , I just don't pay enough attention and put the plane into the wrong spot and that has the immediate effect of making the plane suddenly fly very not-as-smoothly-as-it-was-a-second-ago and really toss it. That's when it's time to just drop the nose, gain speed and head westward into the wind and get out of that mess. I'm pretty jazzed by the experience and call it "good", come in for landing, re-hook the hi-start and try again. So far, the whole thing has been gone by then, so I just hunt for thermals or tree surf or both.

So, that's been my observations, hopefully that gives you something usable. But I think your question is the BIG ONE that's always there.

Hopefully other's can provide more insights/answers.

Thanks for brining it up - Paul
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Old Feb 03, 2012, 09:16 PM
Registered User
United States, OR, Corvallis
Joined Jan 2010
956 Posts
One more thing.....

As CARRINSR brought up - Vultures! Yes!

Vultures and Harriers have taught me more, by watching them, than anything else. By far. I always look forward to the re-appearance of Vultures in the spring and the floaty bobbing motion of the Harriers using lift low to the ground.

Good Times watching those birds.

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Old Feb 03, 2012, 09:23 PM
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United States, MA, Waltham
Joined Dec 2001
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While changes in attitude can be a clue, I find the best way to know if you're in lift is if the plane kind of gets lively. Either it speeds up without dropping or it rises without slowing down. I think there is a visual illusion when the glider starts to go up that makes the tail look high, and it looks low when you're going down.
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Old Feb 03, 2012, 10:13 PM
the flying is good
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USA, CT, Hamden
Joined Oct 2002
2,138 Posts
If the push on the plane is only momentary I don't worry about it but when I have to h-o-l-d the stick over I think more of it. If I've been settling and it happens it's not a part of a thermal, the bump should just be telling you which side the good air is on.
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Old Feb 05, 2012, 08:55 AM
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Joined Jan 2008
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The difference between turbulence, and sink/lift - excellent question.

I really can't tell, but I can tell you that I don't just turn if the airplane bobs a bit.

It depends (I HATE that phrase) on a whole spectrum of conditions, but on quieter, smoother days I find myself turning pretty much any time a wing drops or the airplane surges up. On bumpier days, the airplane has to really rise before I'll venture a turn.

About two years ago, the Arizona Open was held on an incredibly turbulent, windy day. Winds were FAI-max continuously, and it was brutal. In the entire meet, I flew exactly three (3) thermal turns, and they made the difference that day between a mediocre heat, and a max. I can't tell you how I knew to turn when I did, but in my mental look-up table of flight conditions, the "IF-THEN-ELSE" function said "Turn NOW", so I did. Talk about drifting down wind - my fourth turn would have had me in San Diego. Not one other time the whole meet did I attempt a turn. There was no point, it was wind surfing all the way.

In Utah last summer, I observed another atmospheric effect. There was zippo lift one afternoon. It was so quiet, that if two airplanes circled, hawks flew in to check it out (typically, one turn, then flap away!). A local boy kept talking about how "there's usually lift right over there", and with each launch, that's where he'd go, and start circling. Others would see him circle, and join in. Down they would all come, in gentle circles, settling to earth. Fortunately, I was flying next to Jun, and this is what he did: launch high, fly straight out - touch nothing until time to return, then fly straight back. None of the big boys flew in groups. They all flew separate, straight lines, to maximize the search area.

Not much to do with turbulence versus lift, that's just where I chased this particular rabbit.

Yours, Greg
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Old Feb 05, 2012, 09:40 AM
Balsa breaks better
Thermaler's Avatar
Buchanan Mi
Joined Apr 2005
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Originally Posted by carrinsr View Post
I've been in every US state (except Hawaii), and I've observed over several decades literally thousands of turkey vultures (buzzards) as they've flown in just about every imaginable weather condition. I've seen them encounter sudden updrafts and downdrafts, and as they've flown what I call the warmer and cooler "highways in the sky" as they've searched for and found thermals. I've learned much from them. In my opinion they are the true masters of the sky. DC -- Jacksonville, Florida
True masters are the Hawks and eagles, flying smoothly.
Turkey Vultures are more like us, a bit wobbely.
Both have been great teachers for me though.

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Old Feb 05, 2012, 11:06 AM
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Michigan's Upper Peninsula
Joined Sep 2007
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I'll add my two cents as well...heck, you'll soon have a dollar's worth!

I cannot answer your question, but I can offer this: Once my planes get a "push" or I bump into something "up there", I turn into it. It's the only way I can get an idea of whether or not there's lift. Seems to me I am using my plane simply to explore a mass of air. I enjoy trying to unravel the thermal mysteries of places I fly.

What I have learned is that my planes do give me answers about lift. "Yes", "No", but many, many more "Maybes". It's the thrill of the hunt for me.

Happy Hunting,
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Old Feb 05, 2012, 11:31 AM
AMA7224 LSF1832
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United States, DE, Millsboro
Joined Sep 2008
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Originally Posted by Thermaler View Post
True masters are the Hawks and eagles, flying smooth......
Well, when you do it for a living you get good.

I can' tell you exactly how I find lift either. Obvious things would be piggybacking with birds or other sailplanes.Bumps,pushes,nudges all fit in, but somehow you seem to get a "nose" for finding it. As Highride says " .....Yes, No, but many, many more Maybes. It's the thrill of the hunt....."
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Old Feb 05, 2012, 01:54 PM
Chuck 'Em and Chase 'Em
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United States, NY, Plainview
Joined Aug 2005
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I find myself all too often turning in turbulence than lift on those bumpy days.

Is it that my plane is too reactive? At the same token, if it didn't indicate reasonably, then how would I know where lift could be.

When it comes to how much a plane 'indicates' lift is all relative to the pilot. Some like a closer to unstable plane that indicates everything while other like one more muted. I am sure some planes will roll/pitch/yaw a greater number of degrees than others do.

If a plane indicates too well(I'll define this as rolling/yawing/pitching/ a greater number of degrees than another), wouldn't it be a poor plane to fly in turbulent and windy conditions? At the same token, if the plane flies muted and doesn't indicate as greatly, sure it can probably float longer but wouldn't you also fly through the light stuff?

Sure, we all know the telltale signs - birds circling or chasing bugs, bugs or debris higher in the air but I am looking to improve my thermal hunting ability. You know those times when not much is in the air and all you have to go on is wind shifts. Sure, you have the general direction and you know how strong the change is to suggest how far it can be. You go out and search and all too often I find myself 'trying' what could be lift. Sure, I could range father to things that could trip off the lift first but it is hard to pass up something suggestive. So what happens, I fall out of the sky and get less time than if I let the plane just float out and back.

On days where the lift is medium to strong, regular in period and/or localized, it can be like shooting fish in a barrel.

I understand doing the out and in with the same lift several times can be helpful but if you cannot find lift to leave and return to, it is not much good.

Any kind of practice or search patterns or plane setup suggestions would be nice as well.

I was afraid that this is the 'Art' side that cannot be taught and you have to just feel and so far it is turning out to be just that. I will sy that it bugs me to hear someone say, you are turning in lift. I think to myself, 'Idiot, you are flying the plane and your timer can read the air better than you'. I also think that is it me on the sticks that is garbling reading of the lift (since my turn need major work) so my timer believes that the light stuff is me turning in sink?

Keep the help coming and thanks to all.....

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Old Feb 05, 2012, 08:37 PM
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Do you find a lot of thermals, or do you find yourself being frustrated?

How do you climb, when you climb? Do you attempt constant-speed, constant-bank circles? Can your airplane be trimmed into a circle? Do you stick with a thermal for a long time? Do you establish a circle, and keep it?

A lot of thermals announce themselves as turbulence - but with a difference. If your airplane seems to "twitch" a lot when just cruising along, it may be flying a bit slow, or it may have an aft CG.

Mostly, my airplanes (once they are set up the way I like them) are pretty good about showing lift, generally turning right away from thermals. I also set up the controls to be sensitive - then consciously try to keep my thumbs OFF the sticks. Once I decide I'm near a thermal, I turn very quickly into it and establish a steep turn right away, generally 45 degrees.

Yours, Greg
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Old Feb 06, 2012, 06:39 AM
Chuck 'Em and Chase 'Em
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United States, NY, Plainview
Joined Aug 2005
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Finding lift:
depends on the day. Some days it is real easy. I have the hardest times in light lift and overcast days and windy turbulent conditions.

Sometimes it is shooting fish in a barrel. Then there are times I go out after work and find just about nothing.

When I find lift, turns tend to be ugly without lots of control. I mean a carousel horse looks better than I do. At least the horses up and down is regular. Mine, not so much. More like a leaf in the wind. Only when I turn much wider do I tend to oscillate up and down less. Could this be a sign of improper Cg? There are times in medium to higher lift that I find myself turning as if I am pointing downward and turning faster and the plane will bob less.

When I am flying through sink, the plane looks like it is dragging a heavy tail with its nose slightly upward. I see dogs drag their butts like this.


Plane easily wanders form a circle. If I do not hold a
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Old Feb 07, 2012, 09:50 AM
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Well here is the good news: EVERYONE finds light lift hard to work.

I have been told (a long time ago, while I was flying full-scale gliders) that the difference between turbulence and lift is largely up to the pilot. That's the bad news, although it's not entirely true.

I suspect that what you may be seeing is that your own control inputs are masking the behavior of the airplane, and I suggest the following: the basic thermalling discipline is to be able to fly circles at a constant bank, and at a constant airpseed. This works for me.

Once I was able to do that (circles at constant bank, constant airspeed), then any deviation from that path was probably due to air, and I could then count on being able to discern what was lift (as opposed to sink). Concern over turbulence then fell out - instead, if my airplane was unruly, that was when I added ballast. But, the first discipline of thermalling is to be flying constant-bank, constant-speed circles. It requires a smooth touch, by the way.

How much bank? Choose 45 degrees as a first choice: small turn radius, not too much penalty from increased drag due to increased angle of attack. Practically, you will achieve about 30 degrees, but aim for 45.

Camber? Experiment for what gives the most duration in calm air (as calm as you can find, anyway). That will give a slow speed for thermalling, and that reduces turn radius (useful for working smallish thermals).

Between circles, concentrate on flying smooth, which for most of us really means keeping our hands off the controls.

Good luck.

Yours, Greg
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