Which Way is That Thermal?

"Ray Lovinggood" wrote in
message ...
Suppose I'm flying along straight and level and I feel
the left wingtip rise. Where is the thermal? Is it
on the left and is it lifting the wing?

Or, is the right wing in sink and the wing is being
pushed down?

Does that mean there is a thermal further to the right
and the sink that pushed my wing down is the sink that
surrounds the thermal?

Which way should I turn?

For me, the answer is sometimes straight forward:
Turn the way my friends are turning because they got
there sooner than me!

Ray Lovinggood
Carrboro, North Carolina, USA

At 10:48 06 September 2006, Flying_Monkey wrote:
Yes, Frank, please explain this to us. I never heard
that that there
was any other theory than turn toward the uplifted
wing. Sure, there's
lots of theories about what to do after that. Bob
Wander's 'book' has
the 4-circle search method, and it seems like I read
something in
Knauff's stuff somewhere, maybe in 'Breaking the Apron
Strings.' I'm
still early in the learning process, and seem to have
the best results
with 'tighten the turn in decreasing lift, loosen the
turn in
increasing lift. This works so well that I'm frequently
seeing people
in roughly equal gliders climbing past me, so I'm always
looking for a
better way. Enlighten us.

Thanks,
Ed

wrote:
Really? I had never heard of the 'turn away from
the thermal' school
of thought.



Frank Whiteley wrote:
Regarding apparent rising wings, that may not indicate
anything
regarding the direction of the core of the thermal,
other than a turn
may indicated.

That is, there is another school of thought on which
way to turn,
especially if the goal is to center as quickly as
possible in a
thermal.

Frank Whiteley






The only way is up.

Normally the thermal is the opposite way to the way you turn.

You guys must be coming towards winter tonight we are having our first taste
of summer thunderstorm in Sydney.

Summer bush fires blow fly's dust and 10 knot plus thermals bring it on.

Gee, thanks, Ray. :-)

I think it's safe to assume in this discussion that we're talking about
flying alone. If there are other gliders in a thermal, we're required
for many reasons to turn in the same direction that they're turning,
and the presence of other gliders gives us a good idea where to look
for the center. I have my best performance when I can use my neighbors
as thermal indicators. :-)

But this is a serious question. How can I improve my performance
centering thermals? Are all thermals surrounded by this ring of sink
you mention? And what if I fly straight into the middle of a thermal,
so that there's no lifted wing? What's the best technique to use then?

And what about speeds. Lets say I'm flying a Standard class glider,
with a min sink in the mid 40s and a best L/D of 38 at around 57 kt.
What should I be thermalling at in a typical eastern thermal? And what
angle of bank? I typically try to use around 45 degrees, but it isn't
constant until I get the thermal fairly well centered.

TIA (Thanks in advance),
Ed

Ray Lovinggood wrote:
Suppose I'm flying along straight and level and I feel
the left wingtip rise. Where is the thermal? Is it
on the left and is it lifting the wing?

Or, is the right wing in sink and the wing is being
pushed down?

Does that mean there is a thermal further to the right
and the sink that pushed my wing down is the sink that
surrounds the thermal?

Which way should I turn?

For me, the answer is sometimes straight forward:
Turn the way my friends are turning because they got
there sooner than me!

Ray Lovinggood
Carrboro, North Carolina, USA

ContestID67 wrote:
I was sent a link to a gadget some college engineers-in-the-making
built. http://engenius.sece.rmit.edu.au/Abstracts/Page601.htm. It
tries to detect which way a thermal is based on temperature differences
between wing tips. Bright boys.

I have two questions;

1) Have there been other gadgets created to do the same thing? How
well did they work?

2) What do you use to determine if the thermal is on the left or the
right? This is the wing up or down when its near the thermal debate.

Thanks, John

Nothing new there, That system has been tried at least 25 years ago.
It intrigued me, as an electronics engineer just beginning to fly,
but the consensus of the "big boys" at the time was it wouldn't
be sufficiently accurate or too sensitive to random variations
or some other problems.
...lew...

Lew Hartswick wrote:
ContestID67 wrote:
I was sent a link to a gadget some college engineers-in-the-making
built. http://engenius.sece.rmit.edu.au/Abstracts/Page601.htm. It
tries to detect which way a thermal is based on temperature differences
between wing tips. Bright boys.

I have two questions;

1) Have there been other gadgets created to do the same thing? How
well did they work?

2) What do you use to determine if the thermal is on the left or the
right? This is the wing up or down when its near the thermal debate.

Thanks, John

Nothing new there, That system has been tried at least 25 years ago.
It intrigued me, as an electronics engineer just beginning to fly,
but the consensus of the "big boys" at the time was it wouldn't
be sufficiently accurate or too sensitive to random variations
or some other problems.

It might be more practical with today's sensors, far greater computing
power, and electronic attitude indicators that might let you remove
temperature changes caused by bank angle. Or maybe there is a cheap
lidar unit that can detect nearby air motion: mount 3 of them in the
cockpit, pointed in different directions, and maybe get a clue about
where the air is going up and down.

--
Note: email address new as of 9/4/2006
Change "netto" to "net" to email me directly

Eric Greenwell - Washington State, USA

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Lew Hartswick wrote:
ContestID67 wrote:
I was sent a link to a gadget some college engineers-in-the-making
built. http://engenius.sece.rmit.edu.au/Abstracts/Page601.htm. It
tries to detect which way a thermal is based on temperature differences
between wing tips. Bright boys.

I have two questions;

1) Have there been other gadgets created to do the same thing? How
well did they work?

2) What do you use to determine if the thermal is on the left or the
right? This is the wing up or down when its near the thermal debate.

Thanks, John

Nothing new there, That system has been tried at least 25 years ago.
It intrigued me, as an electronics engineer just beginning to fly,
but the consensus of the "big boys" at the time was it wouldn't
be sufficiently accurate or too sensitive to random variations
or some other problems.
...lew...

This measurement technique has never been shown to even work, let alone
be supperior to existing variometers (which it would have to be by a
large margin to justify running wiring thru our wings, although that
might be done by the manufacturer; but they won't do it unless there is
a demand for the device). Personally, I think there are other methods
that will work significantly better than present technology that don't
require you to run wiring in your wings (which would have to be
connected and disconnected every time you assemble/disassemble, which,
in turn, requires an additional preflight inspection).

On the direction to turn: at the last convention I listened to Tom
Knauff declare that most glider pilots don't know which way to turn
into a thermal; the correct direction, according to Knauff, is towards
the down wing because sinking air surrounds a thermal. I am like Eric -
I turn towards the up wing. If Knauff is correct, I should be missing
the thermal (on the 1st turn) well over half of the time, and I am not.
Most of the time I do not immediately commit to the turn (of course,
there is occassionally those 10 kt monsters where there is question),
and actually like to turn slightly away from the direction that I think
the thermal is. The concept here is to find the boundary of the thermal
and to stay inside of it; if you search for the center of the thermal I
think you will end up flying thru it and turning too late, forcing the
glider into the sinking air around the thermal. Once I know where the
boundary is I turn into the thermal, gradually tightening the turn
until I am getting optimum climb. Ideally with this technique you will
seldom fly thru the center of the thermal, making it easier to center
the glider in the thermal. This is also helpful in identifying
streeting, since you turn only once you detect that the lift is
definitely falling off.

Tom Seim
Richland, WA

At 18:36 06 September 2006, Eric Greenwell wrote:
I also turn right most of the time, suggesting most
thermals occur on the right side of my glider, and
I think there are good reasons for that.


OK I'll bite. What good reasons do you have?

Gary Evans wrote:
At 18:36 06 September 2006, Eric Greenwell wrote:
I also turn right most of the time, suggesting most
thermals occur on the right side of my glider, and
I think there are good reasons for that.


OK I'll bite. What good reasons do you have?

I thought you'd never ask! Part of it is some of the thermals will be
entered close enough to center that both wings will rise (20% of them?);
in that case, I circle in my favorite direction. So, if I just flew
randomly about, I'd be circling 40% to the left and 60% to the right.

But, I don't fly randomly: I often have a good idea of where the lift is
(cloud, bird, ridge, dust devil), so I fly slightly to the left of it.
That ups the percentage of thermals on the right (or center) to about
80% overall.


--
Note: email address new as of 9/4/2006
Change "netto" to "net" to email me directly

Eric Greenwell - Washington State, USA

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Here is a way to solve two problems with one action:

When you approach the thermal drop a lot of aluminum confetti. When you
circle around, just fly to the spot that is climbing. At the same time, the
radar operator will spot you on the screen so jets can avoid you.

The problem I have yet to solve is the littering - but you cannot have
everything. Maybe the confetti can be coupons that can be redeemed and the
nearby store operator will pay you to drop them.

I am putting my broken aircraft back together and need to get back in the
air - going stir crazy.

Colin

I agree.

Given that you are in an area of likely lift.
Training stage 1 seems to be how to stay in the thermal when you are
already in it.
Training stage 2 seems to be how to centre in the thermal when you have
found it.
Training stage 3 seems to be how to decide which thermal to centre in
when you are in a likely area.

I have flown a number of legs with Justin Wills on Competition
Enterprise and it is interesting to see our different responses when we
reach the same cloud to climb. I find a good thermal and start centreing
like mad, whilst Justin seems to wander off exploring the area. When I
approach an area already full of other gliders, I will often look around
before joining their thermal.

I often wonder when I meet a thermal whether my first reaction should be
to concentrate on centreing or check that I am in the right place, often
I do the daft thing of first centreing then exploring then re-centreing
which is probably not very efficient.

As for the Immelman, this seems to result from a pull-up from 80kts+ in
neg flap to 50kts in positive flap and a near stall in order to roll the
glider rapidly into the turn. Difficult to achieve in the company of
others.

I am increasingly concerned at my own ability even to manage stage 1.

Rory

Author: Bill Daniels bildan@comcast-dot-net
Date/Time: 20:00 06 September 2006
------------------------------------------------------------
Or, as I've seen in OLC .igc files by top pilots, fly straight through
the thermal to evaluate it, then turn 270 degrees AWAY from the side
where they think the thermal is and then reverse turn direction thus
placing the final

circle two turn diameters back on track offset to the side where the
strongest lift was. The emphasis seems to be good thermal selection vs.

fast centering.

Alternatively, at least one pilot will sometimes perform what must be a

modified Immelmann since the course reversal, as seen on SeeYou's map
view,

is a zero-radius turn while gaining 800 feet in the pull-up. This entry

showed an 80 knot IAS reduction in 12 seconds.

However, it's more likely these guys don't use any specific maneuver -
they just KNOW where the lift is and they're not shy about going for it.

Bill Daniels

ContestID67 wrote:
I was sent a link to a gadget some college engineers-in-the-making
built. http://engenius.sece.rmit.edu.au/Abstracts/Page601.htm. It
tries to detect which way a thermal is based on temperature differences
between wing tips. Bright boys.

I have two questions;

1) Have there been other gadgets created to do the same thing? How
well did they work?

Dear Sir:

Look at the Themi:
http://www.themi.de/Themi%20Centering%20Device.htm

And, I've been told that the Zander flight computer --
http://www.zander-variometer.de/ -- has similar capability, but don't
see evidence of this on their web site.

After hearing about the Themi, I *had* to buy one to see how it works.
Having said that, I have been using one for 2 years, and have some
experience with it -- it's a fun toy -- but I"ve been unable to find
any description of how it operates. Some things are obvious: It has a
GPS engine, and probably has a barometric sensor and/or accelerometers.

In any case, the maximum it coiuld do is to use 3-D GPS data to
calculate climb/descent; it could have accelerometers as well; and
sense pressure changes. It could calculate, therefore, the movement of
the glider, make some assumptions about flight, calculate wind, and on
this basis estimate where the best lift *was* so you can go back to it.

In my experience, if I fly in non-erratic circles, it does a pretty
good job of re-finding the last spots of lift after I've wandered away
fruitlessly looking for something better, and in doing this it seems to
compensate for wind.

Obviously, it can't predict the future, so I use my own judgment on
where lift is *going* to be.

It is useful? After 2 years with it, I do feel that I'm better than it
is. I look at the ground and the cloud (if any) and think about the
wind (my SN-10 is invaluable in this regard --
http://www.ilec-gmbh.com/sn10.htm ) and am reliably able to find lift.

But -- in weak or windy conditions, or when, as sometimes happens, I
lose my mental image of the thermal and where I've been, I will
somtimes turn my brain off for a couple of minutes and just "fly the
lights," and more often than not get back into lift.

I do wish that someone who knows the theory behind this gadget would
speak about this, as it would help me understand how best to fly with
it.