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#81
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In the Jan. 2004 issue of Model Aviation, in the Radio Control Soaring
column, Real Smart Guy candidate Mike Garton proposes a "condensation analogy" to suggest places to look for thermals to trigger. Imagine water condensing on a ceiling: it drips first from the low spots or tiny bumps. Now imagine heated, but relatively stable, air along the ground. If it's "trying" to rise, might it not "drip up" first from the higher spots, little hills, even trees? If it's moving slowly horizontally, and encounters a tree line, it might be forced up enough to trigger a thermal. His experience with models supports the theory on the small scale. Does y'all's experience support it at the larger scale? Roger Worden Same thing with sandy areas - the books say to avoid them like the plague, but the sandy washes here in Arizona are also consistent thermal sources - and like the ponds/tanks, are low discontinuities in the local terrain. In this case, I'm sure it's not the sand that is causing the thermal, my uneducated guess is that the wash channels (or collects) the incipient themal until it gets big and strong enough to break loose. Any Real Smart Guys out there care to give us a serious possible explanation for these effects? - or maybe we need to keep this to ourselves and let the youngsters figure it out for themselves! Got to keep a few tricks in our bags, you know, something about age and experience beating youth and skill... Kirk |
#82
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What you are sying is just about what Reichman says about low level
thermal activity. I did some exercises in a Ka6 (good short landing glider) having a ceiling of 1300ft (I left on track at 1300ft) from takeoff point and over several flights did a 50km ,65kms ,and 102 kms triangles . I was prepared to land out but never had to. Sometimes I would have to drift off track = 10 kms but I kept to the plan. I spent a lot of time between 300-800ft agl but still made good times for that type of soaring. (When I was competing in later years it was a good way to burn off leeching pilots) It did no harm to my placings as I got 2 day placings of 3rd and finished 5th overall in that nationals. It was a fantastic learning experience.. If your terrain is suitable and you are confident of your ability to short land the glider you should do this exercise ,you will learn a lot. gary "Roger Worden" wrote in message m... In the Jan. 2004 issue of Model Aviation, in the Radio Control Soaring column, Real Smart Guy candidate Mike Garton proposes a "condensation analogy" to suggest places to look for thermals to trigger. Imagine water condensing on a ceiling: it drips first from the low spots or tiny bumps. Now imagine heated, but relatively stable, air along the ground. If it's "trying" to rise, might it not "drip up" first from the higher spots, little hills, even trees? If it's moving slowly horizontally, and encounters a tree line, it might be forced up enough to trigger a thermal. His experience with models supports the theory on the small scale. Does y'all's experience support it at the larger scale? Roger Worden Same thing with sandy areas - the books say to avoid them like the plague, but the sandy washes here in Arizona are also consistent thermal sources - and like the ponds/tanks, are low discontinuities in the local terrain. In this case, I'm sure it's not the sand that is causing the thermal, my uneducated guess is that the wash channels (or collects) the incipient themal until it gets big and strong enough to break loose. Any Real Smart Guys out there care to give us a serious possible explanation for these effects? - or maybe we need to keep this to ourselves and let the youngsters figure it out for themselves! Got to keep a few tricks in our bags, you know, something about age and experience beating youth and skill... Kirk |
#83
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Just about 100%. I don't think this is so much a theory as an analogy.
Ian "Roger Worden" wrote in message m... In the Jan. 2004 issue of Model Aviation, in the Radio Control Soaring column, Real Smart Guy candidate Mike Garton proposes a "condensation analogy" to suggest places to look for thermals to trigger. Imagine water condensing on a ceiling: it drips first from the low spots or tiny bumps. Now imagine heated, but relatively stable, air along the ground. If it's "trying" to rise, might it not "drip up" first from the higher spots, little hills, even trees? If it's moving slowly horizontally, and encounters a tree line, it might be forced up enough to trigger a thermal. His experience with models supports the theory on the small scale. Does y'all's experience support it at the larger scale? Roger Worden Same thing with sandy areas - the books say to avoid them like the plague, but the sandy washes here in Arizona are also consistent thermal sources - and like the ponds/tanks, are low discontinuities in the local terrain. In this case, I'm sure it's not the sand that is causing the thermal, my uneducated guess is that the wash channels (or collects) the incipient themal until it gets big and strong enough to break loose. Any Real Smart Guys out there care to give us a serious possible explanation for these effects? - or maybe we need to keep this to ourselves and let the youngsters figure it out for themselves! Got to keep a few tricks in our bags, you know, something about age and experience beating youth and skill... Kirk |
#84
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"K.P. Termaat" wrote in message . ..
I think your way of thinking is correct. I have an equivalent experience for wooded areas. During the day they do not work well, but at dawn when the environment is cooling down they give off their accumulated heat and produce thermals. Karel, NL I expect 99% percent of those reading this will realize *dawn* was probably a translation error, but just in case, I think you meant *dusk* or evening. Andy (GY) |
#85
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From my experience it appears possible for thermals
to form over and rise from a body of water. In the past I have done a great deal of hang glider ridge soaring on the Eastern edge of Lake Michigan. The ridge is a steep sand bluff about 300-400 feet high right on the edge of the water. The water is so close that at some points it touches the base of the bluff. The lake at this point is about 80 miles wide. On rare occasions during light winds just capable of sustaining flight we would encounter what were believed to be thermals. The water would be almost perfectly flat and you could see circular disturbances on the surface moving towards shore at wind speed. When they hit the bluff you could circle up and drift back over the ridge. Our only explanation was clouds that caused uneven heating on the surface of the water were creating the thermals. |
#86
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"Roger Worden" wrote in message om...
In the Jan. 2004 issue of Model Aviation, in the Radio Control Soaring column, Real Smart Guy candidate Mike Garton proposes a "condensation analogy" to suggest places to look for thermals to trigger. Imagine water condensing on a ceiling: it drips first from the low spots or tiny bumps. Now imagine heated, but relatively stable, air along the ground. If it's "trying" to rise, might it not "drip up" first from the higher spots, little hills, even trees? If it's moving slowly horizontally, and encounters a tree line, it might be forced up enough to trigger a thermal. His experience with models supports the theory on the small scale. Does y'all's experience support it at the larger scale? Roger Worden Yes it seems to work that way. A moving object may also disturb motionless hot air and start a thermal. I was once low over a local dirt strip, I think turning base to land, when a truck drove into a large flat dirt area. It triggered a good thermal that got me up and home. Andy (GY) |
#87
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"Andy Durbin" wrote in message om... "Roger Worden" wrote in message om... In the Jan. 2004 issue of Model Aviation, in the Radio Control Soaring column, Real Smart Guy candidate Mike Garton proposes a "condensation analogy" to suggest places to look for thermals to trigger. Imagine water condensing on a ceiling: it drips first from the low spots or tiny bumps. Now imagine heated, but relatively stable, air along the ground. If it's "trying" to rise, might it not "drip up" first from the higher spots, little hills, even trees? If it's moving slowly horizontally, and encounters a tree line, it might be forced up enough to trigger a thermal. His experience with models supports the theory on the small scale. Does y'all's experience support it at the larger scale? Roger Worden Yes it seems to work that way. A moving object may also disturb motionless hot air and start a thermal. I was once low over a local dirt strip, I think turning base to land, when a truck drove into a large flat dirt area. It triggered a good thermal that got me up and home. Andy (GY) One thing to keep in mind is that there is a ratio between thermal triggers and the heated air available to be triggered. In other words, in weak conditions over rugged terrain, there is a surplus of available triggers, but a deficit of heater air to be triggered. Sometimes there will be no thermal over an obvious trigger site because the available bouyant air was already triggered by a lesser, but adequate trigger upwind. In these cases, potential trigger sites are not a reliable thermal indicator. In strong conditions, over mostly uniform, flat surfaces, the few available trigger sites become more important. Bill Daniels |
#88
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Hi Andy,
Thanks for your correction. Meant "dusk" i.s.o. "dawn". Translation error indeed. Though because of my work (american) english is about my second language I made this slip of the pen. Karel, NL "Andy Durbin" schreef in bericht om... "K.P. Termaat" wrote in message . .. I think your way of thinking is correct. I have an equivalent experience for wooded areas. During the day they do not work well, but at dawn when the environment is cooling down they give off their accumulated heat and produce thermals. Karel, NL I expect 99% percent of those reading this will realize *dawn* was probably a translation error, but just in case, I think you meant *dusk* or evening. Andy (GY) |
#89
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Yes I agree. Another example is big cities versus small ones.
I almost never find thermals over the larger areas of housings and buildings belonging to a somewhat larger urban area. Just to many trigger points producing small and low thermals only. However when over a village or a group of farm housings it is usually very easy to find the spot where good thermals are triggered off using the heated air of the direct environment. Karel, NL "Bill Daniels" schreef in bericht hlink.net... "Andy Durbin" wrote in message om... "Roger Worden" wrote in message om... In the Jan. 2004 issue of Model Aviation, in the Radio Control Soaring column, Real Smart Guy candidate Mike Garton proposes a "condensation analogy" to suggest places to look for thermals to trigger. Imagine water condensing on a ceiling: it drips first from the low spots or tiny bumps. Now imagine heated, but relatively stable, air along the ground. If it's "trying" to rise, might it not "drip up" first from the higher spots, little hills, even trees? If it's moving slowly horizontally, and encounters a tree line, it might be forced up enough to trigger a thermal. His experience with models supports the theory on the small scale. Does y'all's experience support it at the larger scale? Roger Worden Yes it seems to work that way. A moving object may also disturb motionless hot air and start a thermal. I was once low over a local dirt strip, I think turning base to land, when a truck drove into a large flat dirt area. It triggered a good thermal that got me up and home. Andy (GY) One thing to keep in mind is that there is a ratio between thermal triggers and the heated air available to be triggered. In other words, in weak conditions over rugged terrain, there is a surplus of available triggers, but a deficit of heater air to be triggered. Sometimes there will be no thermal over an obvious trigger site because the available bouyant air was already triggered by a lesser, but adequate trigger upwind. In these cases, potential trigger sites are not a reliable thermal indicator. In strong conditions, over mostly uniform, flat surfaces, the few available trigger sites become more important. Bill Daniels |
#90
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As regards cities I think it depends...
I once went on a lead and follow course with Andy Davis in blue or partially blue weather. In briefing before flying he would nominate where he was planning to take climbs. In the case of larger towns and cities (Bath, Worcester and Swindon come particularly to mind) he specified where the best thermal source would be and would then take us there as low as possible. If a strong core wasn't there when we arrived he parked us in weak lift and nosed around until he found the next strong pulse. It seemed odd at first to take so much time to do that but it was worth it because he had saved so much more time by ignoring weak lift in the cruise to reach his nominated best thermal source with the minimum of delay and at an altitude low enough to take best advantage of the good climb. So I think that cities will be likely to have at least one source that is better than the multitude of little trigger points John Galloway At 21:24 04 January 2004, K.P. Termaat wrote: Yes I agree. Another example is big cities versus small ones. I almost never find thermals over the larger areas of housings and buildings belonging to a somewhat larger urban area. Just to many trigger points producing small and low thermals only. However when over a village or a group of farm housings it is usually very easy to find the spot where good thermals are triggered off using the heated air of the direct environment. Karel, NL 'Bill Daniels' schreef in bericht thlink.net... 'Andy Durbin' wrote in message om... 'Roger Worden' wrote in message news:... In the Jan. 2004 issue of Model Aviation, in the Radio Control Soaring column, Real Smart Guy candidate Mike Garton proposes a 'condensation analogy' to suggest places to look for thermals to trigger. Imagine water condensing on a ceiling: it drips first from the low spots or tiny bumps. Now imagine heated, but relatively stable, air along the ground. If it's 'trying' to rise, might it not 'drip up' first from the higher spots, little hills, even trees? If it's moving slowly horizontally, and encounters a tree line, it might be forced up enough to trigger a thermal. His experience with models supports the theory on the small scale. Does y'all's experience support it at the larger scale? Roger Worden Yes it seems to work that way. A moving object may also disturb motionless hot air and start a thermal. I was once low over a local dirt strip, I think turning base to land, when a truck drove into a large flat dirt area. It triggered a good thermal that got me up and home. Andy (GY) One thing to keep in mind is that there is a ratio between thermal triggers and the heated air available to be triggered. In other words, in weak conditions over rugged terrain, there is a surplus of available triggers, but a deficit of heater air to be triggered. Sometimes there will be no thermal over an obvious trigger site because the available bouyant air was already triggered by a lesser, but adequate trigger upwind. In these cases, potential trigger sites are not a reliable thermal indicator. In strong conditions, over mostly uniform, flat surfaces, the few available trigger sites become more important. Bill Daniels |
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