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Old Nov 15, 2012, 10:26 AM
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barometric pressure

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Originally Posted by DLGjunkyard View Post
Im not convinced there is a flow of downward air the entire length of the column. Its more about turbulent air around the perimeter , Some of it down air.

Its no different that calm water circling around the edge of a raging river

Varios measure barometric pressure
thank you sir. this is getting more interesting.

this coming from another pilot of full size gliders, makes me think...so vario does not tell there is a downdraft, but change in pressure. right.

now that i thought i had the final answer!
and, as i said before, i remember seeing my planes coming out of a thermal making a stall and recovering and gliding normally, not sinking.
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Old Nov 15, 2012, 11:37 AM
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Image trying to throw your light freeflight glider into one of those dust devils. You cant, it would be spit out .[note the sun tents] Now imagine it sucking that same glider up like it does the dust. Once its inside the core its not likely to penetrate out.If you have ever tried throwing a very light object into a camp fire you have seen the result.

One other thing about varios , they have a lag time. Some compensate for such , others dont.
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Old Nov 15, 2012, 12:43 PM
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inside of the monster

once i read about the beginning of soaring. they were trying to measure the up power of a cumulus. 1 guy got into a cumulus and all became dark, then black, and felt as if he were into a washing machine. all spinning around, so he tried to get out. eventually he managed to, just to find himself (and his plane) upsidedown. so strong was the turbulence that he didn't realize that! same kind happened to another not so lucky guy, whose sailplane was destroyed by the turbulence and, even if he was wearing a safety parachute that opened automatically, when he came out he was dead.
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Old Nov 15, 2012, 01:02 PM
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Walking along the Worthing Sussex sea front Sunday, cool day, very light winds from the NorthEast with clear sky.

Huge flock of seagulls circling over the seafront buildings.

Lowest at about 20mtrs up to the top boys at maybe 60 or 70.

Flying in a clockwise and the flock tipped over towards the South West.

Very clear indication of the size and shape of the thermal breaking off the dark buildings.

be lucky
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Old Nov 15, 2012, 01:06 PM
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I have read about guys using to thermistors ,one out on each wing. The idea is to detect the heat and signal the pilot to turn toward the heat.
http://www.betsybyars.com/guy/soarin.../69-vario.html
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Old Nov 15, 2012, 01:10 PM
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Freakiest thing I ever encountered was soaring a 80 ft coastal bluff in 20 knot winds and climbing to almost a thousand feet. This only happens in late fall with just the proper conditions. A cold front passing over a huge body of water. Water spouts where seen out over the water. Godrich Ontario, in fact
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Old Nov 15, 2012, 02:21 PM
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amazing input

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Originally Posted by DLGjunkyard View Post
I have read about guys using to thermistors ,one out on each wing. The idea is to detect the heat and signal the pilot to turn toward the heat.
http://www.betsybyars.com/guy/soarin.../69-vario.html
thank you for the link. extraordinary information of the several designs.
but now that we know more about varios, is like when you read the ingredients in small print of some food product. sometimes you think that it's better not to know what is inside.
and having to calibrate it for certain altitude in order to get more precise data-just for that altitude...
besides, the more things, the more things can go wrong or fail to provide precise data.

i remember a sign that reads: 'if you can remain calm, maybe is because you do not understand the situation'.
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Old Nov 17, 2012, 04:18 PM
Ochroma Lagopus Tekton
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Originally Posted by Scott Whitney View Post
I do know thermals happen at night;

TRUE STORY: During the 1978 Fall Soaring Festival I decided to fly at night. My Bird of Time was covered in transparent yellow monokote and I had weight reducing holes in all the ribs. I took a long clear plastic tube and filled it with the light emitting goop from a cyalume light stick.

I then slid the tube into the wing and launched my glider. The entire wing glowed making it very easy to see the glider. It was about 10:30 at night and I got a 15 minute flight, playing with a very weak thermal. (never went up very much, just mostly reduced sink)

Over the years I have learned thermals are like women: from a distance they seem similar, but once you get involved you realize they are all different.

Some left me wanting more
Some were boring
Some teased me relentlessly
Some were so frightening I had to leave
Some went away with no warning
And every once in a while one made my fantasies come true.
EXCELLENT simile!
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Old Nov 17, 2012, 04:27 PM
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Originally Posted by phil alvirez View Post
from my memories i recall my planes suddenly tilting, slowing down, closing their turn, raising their nose and almost stalling but not, just climbing: they were into a thermal! but when they were released, there was sort of stalling and away they went. but not sinking, just gliding. occasionally they catched a downdraft, but that was not usual.

so, are really downdrafts at the outside of the conduit that goes up?
if we consider that thermals may develop same way as cumulus do, as they are the start of the cumulus, if we look at a cumulus nimbus forming, do you see any thing going down at the outside? i don't. i just see the whole thing growing up.
it may be downdrafts nearby, but not necessarily so.
that's what i recall.

let's watch more closely next time we get into a thermal and bring our comments.
That I can answer. As warm air rises it cools and the water vapor in it condenses, This creates the cloud. As it reaches the highest altitude it's relevant temperature can take it, it spreads out as the rising air behind it pushes it out of the way; this causes the anvil top of the higher cumulo-nimbus. Once all the vapor is condenced out it there is nothing more to see, so now it is just invisable air. Also as the cooled air sinks, it enters warmer air and any vapor that may be left is no longer condencing out, so again the now sinking air mass is invisible.

One thing this thread is revealing - who really was paying attention in their middle and high school science classes!
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Old Nov 18, 2012, 11:27 AM
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from wiki

some interesting data from wiki:

Cumulus clouds that have formed over the ocean may be found in regularly spaced lines or patterns.These "cloud streets" form when convective currents lying parallel to the ground and each other create updrafts and downdrafts. One current rotates one way, while the two on either side of it rotate in the opposite direction. The distance between the centers of the clouds is three times the height (diameter) of each of the convective currents. The inversion created by the downdraft causes the clear space between the lines of cloud.
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Old Nov 18, 2012, 11:48 AM
greg
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Originally Posted by phil alvirez View Post
Cumulus clouds that have formed over the ocean may be found in regularly spaced lines or patterns.These "cloud streets" form when convective currents lying parallel to the ground and each other create updrafts and downdrafts.
i don't know if it is proper to call clouds formed over oceans "cloud streets". I thought they occur over land. However, consider what happens when cold air moves into a region with warm moist air, including over water. The code front burrows under the warm air raising it. As that warm air cools due to expansion, clouds will form if it reaches the surrounding dew point. Since a front is relatively long and straight there is a long line of clouds. (there also some strange phenomenon that happens in australia causing a long cloud front).

another thing to consider is that when water vapor condenses (opposite of creating steam) it gives up heat, raising the temperature of the now dryer air, which may cause it to rise much further than if the water vapor had not condenced

Quote:
Originally Posted by DLGjunkyard View Post
Varios measure barometric pressure
varios measure the change in pressure and indicate the rate of change (change in altitude). Altimeters measure pressure and relate it to altitude.

greg
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Old Nov 18, 2012, 03:50 PM
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change in pressure

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Originally Posted by ciurpita View Post
varios measure the change in pressure and indicate the rate of change (change in altitude). Altimeters measure pressure and relate it to altitude.
greg


that's how i understood it on post 61: '...so vario does not tell there is a downdraft, but change in pressure. right.'
and show it as a rate of climb or descend.
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Old Nov 18, 2012, 04:54 PM
greg
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Quote:
Originally Posted by phil alvirez View Post
that's how i understood it on post 61: '...so vario does not tell there is a downdraft, but change in pressure. right.'
and show it as a rate of climb or descend.
the vario indicates a change in pressure. Pressure decreases as altitude increases, and increases as altitude decreases. If there is no change in airspeed, the vario is used to indicate lift or sink. If you're in lift, altitude increases. if you're in sink, altitude decreases.

isn't sink the same as what you describe as downdraft?

greg
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Old Nov 18, 2012, 05:44 PM
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up or down

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Originally Posted by ciurpita View Post
the vario indicates a change in pressure. Pressure decreases as altitude increases, and increases as altitude decreases. If there is no change in airspeed, the vario is used to indicate lift or sink. If you're in lift, altitude increases. if you're in sink, altitude decreases.

isn't sink the same as what you describe as downdraft?

greg
well, yes. despite the words, what matters is if your plane hits a thermal or a downdraft. if it is going up or down. and that's what the vario tells.
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Old Nov 23, 2012, 05:55 PM
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The variometers I used to use in full scale sailplanes had a closed vessel. As the airplane rose or fell, air exited or entered the vessel accordingly. The rate at which it went in or out of the vessel (using a thermistor) indicated rate of descent or climb. (Let's see - I got that right: in relates to descent, out relates to ascent)

It has been nearly twenty years since I last went soaring, so I have no idea of what new kinds of varios there are today. I'm probably describing instruments long out-moded.

I once heard a lecture about a guy delivering a motor-glider a long ways, over desolate ground. He was transfering fuel (in flight) from a jerry can to the main tank, when his little fuel pump failed. He (being clever) opened the jerry can and spread a sheet of plastic over the opening, then replaced the lid. With the vent now sealed, he started climbing, and lo and behold, the fuel transferred itself to the main tank! Same principal as a variometer.

Yours, Greg
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