Any sailplane pilots?

Eric Greenwell wrote in message ...
Charles Yeates wrote:
Maybe it is simply an ergonomics thing --- I feel more comfortable
circling to the right in clutch situations simply because it is easier
to pull and adjust rather than push and adjust in right turns.

For me, it's just habit: when I was learning to fly, we'd always get off
tow in a thermal; since we'd always depart tow with a turn to the right,
it was easiest to just continue turning right in the thermal.

For a few flights before a contest, I'll make an effort to fly at least
half my thermals to the left, so I'm ready for the left turns required
at US contests near the start and at turnpoints.

I know a few competition pilots that are definitely "handed", I will
make it a point, when they are in my area, to turn in the direction,
they least prefer. Thanks, Eric

Two out of three thermals (very unscientific study on my part) favor a
right turn. This is the result of the internal circulation of the
thermal. This adds yet another variable to the complexity of
thermalling. I'll leave it up to you to figure out how lift strength,
horizontal and vertical lift profile, vorticity, and turn direction
affect climb performance. Suffice to say in this short note that they
do.

There was a discussion in Soaring (maybe 15 years ago) on this
subject, with a nay sayer concluding, if thermals had spiral
circulation, you could look up and see clouds rotating. Well, I spent
an hour on my back the following weekend and found that they did, and
favored clockwise 2 to 1.

I use the right hand rule. By pointing my thumb up (lift) and curling
my fingers (as in induction fields), I can determine with about 66%
probability the direction of rotation of the thermal as a whole.

A friend of mine (no longer an active glider pilot) used to keep a
careful watch on his yaw string as he entered thermals. He felt that
you could briefly see the direction of rotation and planned his
centering turn in the same direction as its initial deflection. A
talented pilot, I took careful note, though I admit I've defaulted to
always using a right turn unless there are clear indications that I
should turn left (noticeable yaw string deflection, birds, other
gliders, visible shear beneath cloudbase, a dramatic surge up of the
right wing, etc.)

As a side note, I've found that reversing direction is a useful
technique for climbing through a shear. This may be a result of
reverasal of rotation at the top of the inversion layer, but that's
just a guess.

OC

Eric Greenwell wrote in message ...
Charles Yeates wrote:
Maybe it is simply an ergonomics thing --- I feel more comfortable
circling to the right in clutch situations simply because it is easier
to pull and adjust rather than push and adjust in right turns.

For me, it's just habit: when I was learning to fly, we'd always get off
tow in a thermal; since we'd always depart tow with a turn to the right,
it was easiest to just continue turning right in the thermal.

For a few flights before a contest, I'll make an effort to fly at least
half my thermals to the left, so I'm ready for the left turns required
at US contests near the start and at turnpoints.

In Finland we consider it aerobatics to fly right turn in a termal.

Chris OCallaghan wrote:
Two out of three thermals (very unscientific study on my part) favor a
right turn. This is the result of the internal circulation of the
thermal. This adds yet another variable to the complexity of
thermalling. I'll leave it up to you to figure out how lift strength,
horizontal and vertical lift profile, vorticity, and turn direction
affect climb performance. Suffice to say in this short note that they
do.

There was a discussion in Soaring (maybe 15 years ago) on this
subject, with a nay sayer concluding, if thermals had spiral
circulation, you could look up and see clouds rotating. Well, I spent
an hour on my back the following weekend and found that they did, and
favored clockwise 2 to 1.

Where do you fly? I've never seen clouds rotating, and I've been soaring
for 25 years. I have seen dust and other objects in thermals rotating
several thousand feet AGL.

--
-----
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Eric Greenwell
Washington State
USA

Agreed. Circling direction is more often dictated by other gliders in
the thermal than meteorological phenomena and physics.


The protocol I was taught was that unless you are first into the
thermal, you follow the left or right pattern of the gliders already there.
I've never had a preference of right or left. I was taught to turn into
whichever wingtip went up.
I was also taught that the most efficient technique, that is the
highest rate of altitude gain, is in a 45-degree bank turn hopefully
"coring" the thermal.
Up here in the Mojave Desert flying out of IYK, I've been in a couple of
10 Knot thermals but 5 to 6 is the most common. I can't ever remember any
kind of cyclonic rotation of any of them.
That said, I did once, inadvertantly fly into a dust-devil. I NEVER want
to do that again. If I had seen any dust indication that it was there I
would definitely have avoided it in the first place.

Chris OCallaghan wrote:

There was a discussion in Soaring (maybe 15 years ago) on this
subject, with a nay sayer concluding, if thermals had spiral
circulation, you could look up and see clouds rotating. Well, I spent
an hour on my back the following weekend and found that they did, and
favored clockwise 2 to 1.

I use the right hand rule. By pointing my thumb up (lift) and curling
my fingers (as in induction fields), I can determine with about 66%
probability the direction of rotation of the thermal as a whole.


Jack Glendening, among others, have discounted the idea that
something as small as a thermal rotates in a particular
direction due to any Coriolis forces.

However, I carefully examined my .igc files for
extended climbs in thermals, and found that my climb
looks like a "corkscrew." I'm not talking about
the path of the glider, but the center of the
thermal at the various altitudes. As far as I can tell,
this had nothing to do with the direction the
wind rotates in the thermal, but is simply the thermal
itself not going "up" straight (or even slanted evenly
due to wind). So perhaps coriolis affects the thermal, or
perhaps it affects the way the GPS readings are determined.
In either case, I'll need to go back and look again at
these traces.

Has anyone else noticed that the core of the thermal
they are climbing in seems to rise like a corkscrew
with altitude? Does anyone have a hypothesis about if
it is an effect on the thermal, or on the GPS?

On Mon, 29 Dec 2003 02:02:43 GMT, "Casey Wilson"
wrote:

That said, I did once, inadvertantly fly into a dust-devil. I NEVER want
to do that again. If I had seen any dust indication that it was there I
would definitely have avoided it in the first place.

Could you tell more please?
This is one of the things that I've been thinking about for a long
time.


Bye
Andreas

Casey Wilson wrote:

That said, I did once, inadvertantly fly into a dust-devil. I NEVER want
to do that again. If I had seen any dust indication that it was there I
would definitely have avoided it in the first place.

No dust, no dust devil! But, of course, the thermal can still be there.
Coming into one low can be dangerous, but up here in eastern Washington
State, we use them frequently, especially on blue days. They are usually
quite tame. Only the biggest are potentially dangerous, and then only
when "near" the ground (say, less then 1500 feet AGL).

What you are flying makes a difference, too: a 1-26 is going to be
tossed around a lot more than an ASW 20 with ballast. Flying faster than
the normal thermalling speed helps quite a bit if the thermal is rough.


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

Eric Greenwell
Washington State
USA

"Mark James Boyd" wrote in message
news:3fefacf7$1@darkstar...
Chris OCallaghan wrote:

There was a discussion in Soaring (maybe 15 years ago) on this
subject, with a nay sayer concluding, if thermals had spiral
circulation, you could look up and see clouds rotating. Well, I spent
an hour on my back the following weekend and found that they did, and
favored clockwise 2 to 1.

I use the right hand rule. By pointing my thumb up (lift) and curling
my fingers (as in induction fields), I can determine with about 66%
probability the direction of rotation of the thermal as a whole.


Jack Glendening, among others, have discounted the idea that
something as small as a thermal rotates in a particular
direction due to any Coriolis forces.

However, I carefully examined my .igc files for
extended climbs in thermals, and found that my climb
looks like a "corkscrew." I'm not talking about
the path of the glider, but the center of the
thermal at the various altitudes. As far as I can tell,
this had nothing to do with the direction the
wind rotates in the thermal, but is simply the thermal
itself not going "up" straight (or even slanted evenly
due to wind). So perhaps coriolis affects the thermal, or
perhaps it affects the way the GPS readings are determined.
In either case, I'll need to go back and look again at
these traces.

Has anyone else noticed that the core of the thermal
they are climbing in seems to rise like a corkscrew
with altitude? Does anyone have a hypothesis about if
it is an effect on the thermal, or on the GPS?


According to some published research by Wayne Angevine,
http://cires.colorado.edu/ and NOAA, and the results of analysing thermic
activity with lidar and IR methods in the mid-1990's, you might do better to
think of thermals as plume-like. You may transit one or more plumes in a
thermaling turn and plumes may merge into larger plumes while rising.
Merging would seem to account for those lateral shifts, strengthening gusts,
and some rotational effects. Transiting multiple smaller plumes might
explain why some thermals appear to have two or more 'cores' or are hard to
center.

Wayne spoke at our club on this a few years back. His article was published
in one of the model magazines and research presented at the CIRES
gatherings. One of his grad student researchers was a collegiate member of
our club during this period. Wayne's specialty is atmospheric boundary
layer physics.

Frank Whiteley

http://www.rc-soar.com/tech/thermals.htm

Early version of Wayne's work. He presented us with quite a detailed
display of a cubic mile of atmospheric activity.

Frank

"F.L. Whiteley" wrote in message
...

"Mark James Boyd" wrote in message
news:3fefacf7$1@darkstar...
Chris OCallaghan wrote:

There was a discussion in Soaring (maybe 15 years ago) on this
subject, with a nay sayer concluding, if thermals had spiral
circulation, you could look up and see clouds rotating. Well, I spent
an hour on my back the following weekend and found that they did, and
favored clockwise 2 to 1.

I use the right hand rule. By pointing my thumb up (lift) and curling
my fingers (as in induction fields), I can determine with about 66%
probability the direction of rotation of the thermal as a whole.


Jack Glendening, among others, have discounted the idea that
something as small as a thermal rotates in a particular
direction due to any Coriolis forces.

However, I carefully examined my .igc files for
extended climbs in thermals, and found that my climb
looks like a "corkscrew." I'm not talking about
the path of the glider, but the center of the
thermal at the various altitudes. As far as I can tell,
this had nothing to do with the direction the
wind rotates in the thermal, but is simply the thermal
itself not going "up" straight (or even slanted evenly
due to wind). So perhaps coriolis affects the thermal, or
perhaps it affects the way the GPS readings are determined.
In either case, I'll need to go back and look again at
these traces.

Has anyone else noticed that the core of the thermal
they are climbing in seems to rise like a corkscrew
with altitude? Does anyone have a hypothesis about if
it is an effect on the thermal, or on the GPS?


According to some published research by Wayne Angevine,
http://cires.colorado.edu/ and NOAA, and the results of analysing thermic
activity with lidar and IR methods in the mid-1990's, you might do better
to
think of thermals as plume-like. You may transit one or more plumes in a
thermaling turn and plumes may merge into larger plumes while rising.
Merging would seem to account for those lateral shifts, strengthening
gusts,
and some rotational effects. Transiting multiple smaller plumes might
explain why some thermals appear to have two or more 'cores' or are hard
to
center.

Wayne spoke at our club on this a few years back. His article was
published
in one of the model magazines and research presented at the CIRES
gatherings. One of his grad student researchers was a collegiate member
of
our club during this period. Wayne's specialty is atmospheric boundary
layer physics.

Frank Whiteley