Any sailplane pilots?

I am not disputing the facts, I am disputing the explanation.

Mike
MU-2


"Andy Durbin" wrote in message
om...
"Mike Rapoport" wrote in message
link.net...


You will find less lift over water of any kind, even if it is contained
in
vegetation. The best lift is always over the highest, dryest, darkest
surface around. The water vapor idea is...well...it is hard to find a
place
to start...but it won't work

Mike
MU-2


I hope you come and fly with us in Arizona some time. After a few
miles of cross country in the blue you may come to appreciate the
thermals triggered by the small ponds known as cattle tanks.

Been using them for over 15 years and no theororetical analysis will
convince me they dont work.


Andy (GY)

Mike Rapoport wrote:

"K.P. Termaat" wrote in message
...
Thanks Larry for your interesting respons with your links to the articles.


Talking about a drain and water brings me to the idea of telling that when
low and looking for a thermal I always try to locate small ponds in dry
areas. It looks to me that the water vapor rising from these ponds is an
excellent means of starting a thermal. Water vapor is lighter then air, so
it increases the boyancy of the air over the pond and off it goes.
Starting
at about ground level, circling to the right may then generally be the
better option. Any experience with this Larry?

Karel, NL

You will find less lift over water of any kind, even if it is contained in
vegetation. The best lift is always over the highest, dryest, darkest
surface around. The water vapor idea is...well...it is hard to find a place
to start...but it won't work

Mike
MU-2

As I just posted in the "water vapour" thread, I think you have it all back the front.
Have seen similar effects over the small dams on farms here too. My idea is that the air over the
water cools by evaporating water out of the pond. In so doing it looses more heat and hence
contracts more (gets denser) than it gains buoyancy by water vapour increase, ie, it gets both
colder and denser overall than the surrounding surface air. As the dense pool of air becomes
greater, it spreads out, ie, sort of collapses on itself, and pushes out over the edges of the pond
/ dam, particularly down slope over the dam wall, creating a miniature equivalent of a valley wind
in the creek or down the slope, thus acting as a wedge trigger to lift the warm dry air off the
ground.

Frank, your description of Wayne's model is closest to my own
observation. There is perceptible vorticity in cumulus clouds, both on
a macro and micro scale (within the limits of the thermal), that is,
you can perceive a slow turning of the cloud as a whole, while
numerous smaller vortices are encompassed within it. I will read
Wayne's work with interest. To those that ascribe to the theory that
there is no rotation of the thermal, I would begin with the prompt to
"look up." Best if you can take 20 to 30 minutes and watch a thermal
throughout its life.

Mark,

Are you referring to a sinuousness or serpentine bending in the
vertical path of the core? That is, bending like some narrow cored
tornados?

I am not disputing the facts, I am disputing the explanation.


OK, Its time for my Minden pond theory. We have a small pond about 5 miles east
of the airport that consistently produces thermals. JJ's explanation; Heated
air that is slowely moving over the ground by the wind, suddenly comes to the
cooler pond edge. This cool edge of the pond acts as a trigger that forces the
heated air to break loose and start rising and that's why thermals can be found
at the edge of small ponds.
JJ Sinclair

On Mon, 29 Dec 2003 14:11:24 GMT, "William W. Plummer"
wrote in Message-Id:
gCWHb.163786$8y1.490686@attbi_s52:

I used to wonder why the default for holds is to the
right but the default for VFR patterns at airports is left. --Bill

That is how I found my best thermal ever. Flying my HP16T at a Region
8 contest in Eric's stomping grounds. It was about 2 hours into a 3
Hour post task and front started moving into the area. I decided that
getting home might score better than trying to make the minimum time
and landing out so I headed back to the airport under the cloud deck.
The Glide was totally smooth and I arrived back at the airport at
about 1500 AGL. (~3000MSL) on the far side of the airport the sun was
shining and I could see two large dust devils up on the hill from the
airport. As I approached closer dust devil I could see cheat grass,
tumble weeds and garbage bags floating around in it. I put my left
wing into the dust devil and turned hard left. My 10kt vario pegged. I
switched the scale to 20kts and it pegged again. It would occasionall
drop to as low as 16kts. I went from 3000MSL to 11000MSL in about 4
minutes averaging right at 20kts. I had to stop the climb due to cloud
bases. From there I did a final glide out to a turnpoint and back to
the airport to finish within a few minutes of the 3 hour minimum.
Looking out on the wing I could see cheat grass draped all along the
leading edge of the wing. I am sure it didn't due anything good to my
glide ratio. As I rolled to a stop at the airport all the Cheat grass
dropped off the wing onto the tarmac, which made for a great story
"There I was, so low that..."

Brian
HP16T



Eric Greenwell wrote in message ...
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.

On the other hand I can't tell you how many times(numerous) I
intercepted a dust devil at 1000-1500 AGL and climbed out at less then
1kt or even did not climb. Most times however I get 3-6 kts out of
them. I have see dust devils go to 7-8000 feet up. Hate to tell the
one gentleman this that wouldn't fly into a dust devil, but if he flys
using thermals he is just flying into dustless dust devils, As far as
I can tell the only difference is if it is lifting air over an area
were it can pick dust up or not.

Brian
HP16T



Eric Greenwell wrote in message ...
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.

"Chris OCallaghan" wrote in message
om...
Frank, your description of Wayne's model is closest to my own
observation. There is perceptible vorticity in cumulus clouds, both on
a macro and micro scale (within the limits of the thermal), that is,
you can perceive a slow turning of the cloud as a whole, while
numerous smaller vortices are encompassed within it. I will read
Wayne's work with interest. To those that ascribe to the theory that
there is no rotation of the thermal, I would begin with the prompt to
"look up." Best if you can take 20 to 30 minutes and watch a thermal
throughout its life.

There's a later article in one of the modeling magazines complete with the
graphics (unfortunately I've don't recall these being reproduced on the web)
and more analysis. We'd asked to see if it could be re-published in
soaring, but apparently the those rights weren't available. Wayne is an RC
enthusiast AFAIK, the thermal modeling he showed us at the club talk
indicated plumes at higher altitudes than mentioned in the link. I believe
the CIRES team returned to the same cubic mile of air for 4-5 years and I
think it was in Illinois or perhaps Indiana (have to dig back), so he
modeling of thermals deals with some specific topography and weather
patterns. Funding was always an issue. He did say that the most reliable
thermal finder would need to 'see' detritous in the air.

Frank

Eric,

Look up!

I know, it's pretty impolite of me. I assure you it is nothing
personal against you in particular. Many, many pilots share your
opinion. I guess I find it very frustrating to have to explain the
obvious. Or. more to the point, to have to argue for the sake of the
obvious. My preference would be to move to the next level, to discuss
what the real effects of vorticity are on soaring flight. Instead, we
wallow about trying to apply models to decide the truth about
something easily observed.

Granted, our attention spans are short, but spending a half hour on
your back watching the development of a cumulus cloud can be very
instructive. But you needn't even do this if you are observant during
your climbs. You will note that around the edges of the cloud you'll
occasionally see vortices forming when the light hits them right. Or
if there is clag below cloud base, it will often have a discernable
rotation. When observed, they often herald localized cores that can be
exploited. More than once I've noted vorticity on the edege of a large
cloud, shifted my circle to it, and been rewarded with much improved
lift.

Spending some time on your back, you will observe that not only are
there localized vortices, but that the entire system slowly rotates.
Sometimes it's easier to see this than at others. However, patience is
required since the rotation is very slow, but nontheless discernable.
Best to start with a wisp and watch its full development. Choose one
as close to directly overhead as possible. The closer your view to
directly beneath, the more obvious the cloud rotation becomes.

I was hoping that the accelerated cloudscapes in Going the Distance
would make this obvious, but most of the clouds are shot at very low
angles. This makes discering the rotation more difficult as it is
overpowered by the vertical development and dissipation of the cloud.
By viewing from directly beneath, you won't be distracted by this.

Perhaps someone with the appropriate video recording capabilities
could do some time lapse photography and offer it up for review.