Sharing a thermal

I'm a little confused by who is writing what and to whom, but each
person has their own peculiar theory of thermalling. Hal was
interested, as best as I could tell, in maximizing his climb. The
approach I suggested gets you into the better lift as quickly as
possible, and establishes a new "center" for others in the thermal to
join. If you have found the better lift, others will join you. If not,
you'll adjust back into the original center.

I find that only a handful of pilots actively seek the best part of
the thermal. Most are content to accept a circle that provides
relatively uniform lift all the way around. This means that I often
find myself conflicting with other gliders. But only briefly, as I'm
usually above them within a turn or two. I'll note that I do not fly
this way around the home drome... These are techniques for racing and
assume the people in a thermal understand that we are all trying to
get around the course as quickly as possible. Achieving a consistently
high climb rate has a dramatic impact on your x-c speed... so more
often than not, when I find the core (that is, the "real" core),
everyone else in the thermal quickly joins in.

If Hal is interested in maximizing his climb rate (which means getting
into the best available lift as quickly as possible), he needs to fly
aggressively. However, those who appreciate soaring for its tanquility
may not appreciate his enthusiasm, or particularly care that they're
not in the best lift. One adjusts as necessary to one's surroundings.

As for close quarters at 60 degrees... bring it on. I love flying with
pilots who can sustain a steep turn in the core. Great views, great
fun. And chances are good that all the pilots in there with you know
how to fly.

Years ago, at a contest in Corning, NY I entered a thermal at no more
than 400 feet above the ground. It was to my right, so I cleared and
started turn to the right. I found about 2 knots. After gaining a few
hundred feet I heard a call on the radio: "Five Niner, you're turning
the wrong way!" I nearly broke my neck trying to see who I was about
to hit. After two more turns, I looked up to see a Libelle 4,000 feet
above, nearly at cloudbase. (I should note that 59 had a very
distinctive paint job and 3-foot high winglets -- visible from miles
away). I keyed the mike... "Libelle, are you talking to me?"

"Yes, you're turning the wrong way."

It wasn't worth the effort to explain why I was turning right... or
why he shouldn't care. Within another turn he'd left the thermal. End
of discussion.

OC

Let's hope you two guys don't meet up in the same thermal!
I believe we have the makings here of a two-party
system on thermalling. Let's hope it doesn't get vicious.

Some of us don't even have a theory; we just blunder
around.

Don't worry... I'll be above him in half a turn. And I'll have cold
beers waiting for both of you at the finish line. ;-)

I like the trash talk, Chris. Did you ever paly basketball?

"Todd Pattist" wrote in message
...
(Chris OCallaghan) wrote:

I'm a little confused by who is writing what and to whom, but each
person has their own peculiar theory of thermalling. Hal was
interested, as best as I could tell, in maximizing his climb. The
approach I suggested gets you into the better lift as quickly as
possible, and establishes a new "center" for others in the thermal to
join.

I'm as interested as you in getting to the new center
quickly, but here is the scenario: you and I are at the same
altitude on opposite sides of a turn, and you are on the
weak side, I'm on the strong side. I desperately want to
turn tighter so I can stay in the lift and skip the weak
lift you're in. I'm going to tighten as much as I can and
still be clear of you .

The problem is that you suggested tightening first on the
weak side, then opening up. Aside from the fact that I don't
see much advantage in tightening on a weak side, if you
tighten, I can't tighten, as that puts us both head on if
you don't open up. Since most pilots will tighten in strong
cores, when I see you tighten, I've got to consider that
you're mistaken as to the location of the core.

We have the same problem if you're on the strong side, and
I'm on the weak. If I use your method of tightening in the
sink, you can't safely tighten in the strong lift because
I've turned into the space you need.

Bottom line, when we're at the same altitude, some
cooperation will be both safer and better for both of us.
We'll get the lift cored faster if we tighten in lift, not
sink.
Todd Pattist - "WH" Ventus C
(Remove DONTSPAMME from address to email reply.)

I went back and plotted the glider paths to scale using turn math. My
suggestion to reduce the bank by 15 degrees at the weakest point works
perfectly and creates no problem even if the pilot opposite tightens his
turn in the strongest lift. This isn't my idea, I think it was Klaus
Holighaus who originally wrote about it.

It's a bit counter-intuitive but an 8-second 180 degree turn at reduced bank
will place you in perfect position to tighten up in the core, or at least
you will have moved the turn center directly toward the strongest lift.
It's also much easier to keep track of other gliders at a lessened bank.
The small control deflections required are very efficient.

Violent maneuvering to center the core has several disadvantages. It's very
draggy to fly with large control deflections, it's harder to do the mental
dead reckoning to keep track of the direction to the stronger lift and it
risks collision with possibly unseen gliders.

To summarize, at the weakest point of the turn, lessen the bank by exactly
15 degrees (45 to 30 for example) and then hold that bank and airspeed for
180 degrees of turn and then increase the bank again to 45. This moves the
circle center roughly one turn diameter in the direction of the stronger
lift. It's a very gentle maneuver and it is easy to do. It just takes some
patience to stick with it through the 180 turn.

Bill Daniels

"Todd Pattist" wrote in message
...
"Bill Daniels" wrote:

I went back and plotted the glider paths to scale using turn math. My
suggestion to reduce the bank by 15 degrees at the weakest point works
perfectly

I don't have a problem with reducing the bank on the weak
side. That's what I recommend too. I had a problem with
*tightening* the bank on the weak side.

Here is what I was responding to:

"You see better lift on the south side of the circle. Your
are on the north side (facing West - turning left) Steepen
up (60 degress) (sic) through 90 degrees of turn, until you
are facing south"

Violent maneuvering to center the core has several disadvantages. It's
very
draggy to fly with large control deflections, it's harder to do the
mental
dead reckoning to keep track of the direction to the stronger lift and it
risks collision with possibly unseen gliders.

I completely agree. there's no reason to tighten in sink
first, then open, then tighten again.

Todd Pattist - "WH" Ventus C
(Remove DONTSPAMME from address to email reply.)

Todd, I believe that your method works but, if I understand what you are
saying, I have one reservation about it.

The time that it takes to level the wings from 45 degrees is about 2-3
seconds during which time you will have traveled about 200 to 300 feet in a
more-or-less straight line. (Estimating true airspeed at 100 FPS). It's
about the same time and distance to resume the 45 degree bank.

Resisting the temptation to roll through large angles is a good thing.
Changing from 45 to 30 or back can be done in less than a second while
traveling only about 100 feet. The glider is more efficient at 30 degree
bank so any losses during the 180 are small. During the 180 you can use the
time to re-acquire any gliders you may have lost track of.

Thermalling with those few pilots who use this method is like a beautiful
waltz toward the thermal core. It's very relaxing compared to flying with
pilots who make unpredictable moves to center the thermal. My waltz partner
and I almost always top the thermal first leaving the yank and bank "fighter
jocks" far below.

Thermalling with a pilot who can lock in on the opposite side of the turn is
one of soaring most beautiful experiences. He just seems to hang there in
space with no relative velocity as you both turn about the same center.
Even though he is very close, there is no danger since he is heading the
opposite direction all the time.

Bill Daniels

How much of this depends on the reaction time of the
vario?

I'm sure that textbooks from 40 years ago said to tighten
up in sink and open out in lift. As a matter of fact,
I believe this is one of the methods described by Reichmann.
This can make sense if the tightening if it is slight
and takes place early on the sink side, followed quickly
by opening up again. Such a move would tend to move
the circle toward the core, but would be disastrous
if done late.

I agree that opening out will enlarge the circle such
that the opposite side will then move toward the center.


At 17:12 18 October 2004, Todd Pattist wrote:
'Bill Daniels' wrote:

Todd, I believe that your method works but, if I understand
what you are
saying, I have one reservation about it.

I'm not sure I spent much effort describing 'my' centering
method. I was concerned about a technique being recommended
to a beginner that called for excessive maneuvering
in close
quarters that was the opposite of what most pilots
do.

There are lots of commonly used techniques that the
other
pilot can use - and that 1) I'm comfortable with,
2) I will
recognize, and 3) I can adapt to and work with. He
can roll
level at 90 degrees from the weak point. He can simply
reduce bank slightly to shift towards the center.
If he's
got longer wings, he may just slip it towards the center.
For all these common techniques, if he goes first,
it's easy
to see what he's doing. and I can move in tighter
behind
him so we're both well centered in the core.

The one thing that will screw us both up is if he tightens
up in the sink.

Personally, I use whatever works. As soon as I figure
out
which direction to go, and provided he hasn't made
a move
yet, I'll try to shift and signal to him where I think
we
should go. How much I shift and the technique I use
can
depend on lots of factors.

Long wings and strong tight core with a small centering
distance? - I may just slip it over.

Near the top, lift weakening and I'm willing to leave,
but I
think there might be some better lift in the on-course
direction? I'll probably roll it level, then roll
back in
if it improves, but keep going if not.

Big center change to make? Probably roll it level.

Normal centering adjustment? I'll reduce bank as needed
as
I pass the weak side and/or tighten in the best lift.
Even
this has lots of variations. Is the other pilot flying
with
too little bank? I may turn inside in the strong core.
Is
it a student in a 2-33 and I'm just climbing to start
altitude? I'll be less aggressive. Is he ahead of
me or
behind me in the circle? I may combine the centering
with a
position adjustment to get opposite him.


Todd Pattist - 'WH' Ventus C
(Remove DONTSPAMME from address to email reply.)

"Nyal Williams" wrote in message
...
How much of this depends on the reaction time of the
vario?


A lot.

Most vario's have a time constant of about 2-3 seconds or more. I put a
bunch of different varios on a test bench last winter and found some were as
bad as 11 seconds. The average 45 degree bank thermalling turn takes about
13 - 14 seconds so a 3 second delay can be a quarter turn. Some vario's
respond more quickly with the onset of lift but can take much longer to
return to zero after the lift ends.

FWIW, Mike Borgelts varios were the best of the lot on my test bench.

This means that you have to pay attention to the "whack it the back" (or
"whump in the rump" in the case of a 2-33) feel as you enter a thermal. If
you must watch the vario, figure a 60 degree of turn correction for vario
lag.

All this points up the need for an "inertial vario" that integrates the
vertical acceleration to display rate-of-climb. An inertial vario would
have no lag, no noise since it is damped by the mass of the glider and
should be dead accurate. UAV MEMS AHRS (Attitude Heading Reference Systems)
with three orthogonal gyros and accelerometers are in the $1000 range.
They'd make a fabulous vario. I'd love to have an instrument with a 1:1
correlation with the seat-of-the pants feel.

Bill Daniels

Nyal Williams wrote:
How much of this depends on the reaction time of the
vario?

I'm sure that textbooks from 40 years ago said to tighten
up in sink and open out in lift. As a matter of fact,
I believe this is one of the methods described by Reichmann.


By the way, it is what i have been learnt to do, and it seems
to work :-)



--

Michel TALON

Bill Daniels wrote:


Most vario's have a time constant of about 2-3 seconds or more. I put a
bunch of different varios on a test bench last winter and found some were as
bad as 11 seconds. The average 45 degree bank thermalling turn takes about
13 - 14 seconds

Yikes! I don't know what you are flying, but it takes my ASH 26 about 27
seconds to make one turn (50 kts IAS, 8000' msl, 8.2 lb/sq ft wing
loading). That's measured from a flight trace. My ASW 20 was a little
quicker, flying at 7.5 lb/sq ft, but nothing like 14 seconds.

so a 3 second delay can be a quarter turn. Some vario's
respond more quickly with the onset of lift but can take much longer to
return to zero after the lift ends.

FWIW, Mike Borgelts varios were the best of the lot on my test bench.

How did the 302 compare, what did you have the time constants set at,
and where you judging by the needle or the audio?


This means that you have to pay attention to the "whack it the back" (or
"whump in the rump" in the case of a 2-33) feel as you enter a thermal. If
you must watch the vario, figure a 60 degree of turn correction for vario
lag.

At least with my glider and my vario, it seems to be less than 20
degrees, and I can ignore it, since the glider doesn't respond quickly
enough. Flying small gliders (11 meter SparrowHawk, 12 meter Russia,
etc.) will surely change the equation.


All this points up the need for an "inertial vario" that integrates the
vertical acceleration to display rate-of-climb. An inertial vario would
have no lag, no noise since it is damped by the mass of the glider and
should be dead accurate. UAV MEMS AHRS (Attitude Heading Reference Systems)
with three orthogonal gyros and accelerometers are in the $1000 range.
They'd make a fabulous vario. I'd love to have an instrument with a 1:1
correlation with the seat-of-the pants feel.

I'm guessing the hard part for an inertial vario would be ignoring stick
thermals.


--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

"Eric Greenwell" wrote in message
...

Yikes! I don't know what you are flying, but it takes my ASH 26 about 27
seconds to make one turn (50 kts IAS, 8000' msl, 8.2 lb/sq ft wing
loading). That's measured from a flight trace. My ASW 20 was a little
quicker, flying at 7.5 lb/sq ft, but nothing like 14 seconds.

You might re-check your bank angle and your static port position error. 27
seconds seems too long.

I fly a Nimbus 2C and I do turn tight. At 6lbs PSF I usually thermal at
45-55 degree bank at 40 MPH. I checked the elapsed time with the sweep
second hand on the panel clock. At 11 PSF the 45 degree bank Vmin sink goes
up to 55mph or so. (One of these days, I'll get an ASI in knots.)

Although, I did look at some flight recorder traces of the Nimbus thermaling
at 17,999 feet on a hot summer day with the ballast tanks full. The turns
were 2000 feet in diameter.

OTOH, a good 1-26 driver can rip off a 360 in 10 seconds.

How did the 302 compare, what did you have the time constants set at,
and where you judging by the needle or the audio?

I didn't check the 302.


I'm guessing the hard part for an inertial vario would be ignoring stick
thermals.

TE compensation can be done by the same computer that integrates the
acceleration.

Bill Daniels