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#11
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Where is the next thermal?
Can I agree with Andy. In the UK we often seem to get really strong
thermals close to a large lake or reservoir such as Grafham Water. The thermals are coming off the surrounding land of course, but the temperature contrast between the hotter ground and the cooler water seems to act as a trigger mechanism or a mini front. I have often found that discontinuities such as the edge of a forest, a ridge line (especially if pointing into sun), or a ploughed field next to one with crop often seem to give thermals. Provincial towns and active power stations are also good ground sources. However the most reliable thermal markers are circling birds of prey such as buzzards or kites, or insect eaters such as swallows and swifts. Derek Copeland At 22:28 21 September 2009, Andy wrote: On Sep 21, 1:52=A0pm, danlj wrote: I hope this turns into a thread on "How I keep going" - there must be scores of pilots more excellent than I who can say more than me. I well remember that years ago when a visiting German pilot asked for advice on finding thermals in Arizona I told him to look above and downwind of cattle tanks. These are known as stock ponds in other places. His reaction, that I must be a complete idiot for suggesting that pools of water could trigger thermals, has made me cautious about offering that advice to anyone. I hoped he landed out but I don't think he did. Andy |
#12
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Where is the next thermal?
On Sep 22, 2:00*am, Derek Copeland wrote:
Can I agree with Andy. In the UK we often seem to get really strong thermals close to a large lake or reservoir such as Grafham Water. The thermals are coming off the surrounding land of course, but the temperature contrast between the hotter ground and the cooler water seems to act as a trigger mechanism or a mini front. I have often found that discontinuities such as the edge of a forest, a ridge line (especially if pointing into sun), or a ploughed field next to one with crop often seem to give thermals. Provincial towns and active power stations are also good ground sources. However the most reliable thermal markers are circling birds of prey such as buzzards or kites, or insect eaters such as swallows and swifts. Derek Copeland * At 22:28 21 September 2009, Andy wrote: On Sep 21, 1:52=A0pm, danlj *wrote: I hope this turns into a thread on "How I keep going" - there must be scores of pilots more excellent than I who can say more than me. I well remember that years ago when a visiting German pilot asked for advice on finding thermals in Arizona I told him to look above and downwind of cattle tanks. *These are known as stock ponds in other places. *His reaction, that I must be a complete idiot for suggesting that pools of water could trigger thermals, has made me cautious about offering that advice to anyone. *I hoped he landed out but I don't think he did. Andy Andy's observation is a secret well-known to cross-country pilots in Arizona. Sometimes the most ridiculously small and almost dry water holes will be the source of strong thermals. My theory is that water holes inject enough moisture into the hot dry air to significantly increase its buoyancy. We also have small hills consisting of black volcanic rock that are also good sources. Dry river beds (called washes in the southwest US) also can be useful sources. Another issue with clouds here is that on fairly dry days the top of the lift is often a thousand feet or more below cloud base. However, a strong thermal will often continue for a short time above the top of lift fueled by the extra heat released by condensation and eventually form a cumulus. Once this short thermal pulse has decayed, the area immediately below the cloud then has no lift, although the original thermal may still be found a few thousand feet below. I call these clouds "cumulus decoyus" - decoy cumulus! Mike |
#13
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Where is the next thermal?
On Sep 22, 11:40*am, Mike the Strike wrote:
On Sep 22, 2:00*am, Derek Copeland wrote: Can I agree with Andy. In the UK we often seem to get really strong thermals close to a large lake or reservoir such as Grafham Water. The thermals are coming off the surrounding land of course, but the temperature contrast between the hotter ground and the cooler water seems to act as a trigger mechanism or a mini front. I have often found that discontinuities such as the edge of a forest, a ridge line (especially if pointing into sun), or a ploughed field next to one with crop often seem to give thermals. Provincial towns and active power stations are also good ground sources. However the most reliable thermal markers are circling birds of prey such as buzzards or kites, or insect eaters such as swallows and swifts. Derek Copeland * At 22:28 21 September 2009, Andy wrote: On Sep 21, 1:52=A0pm, danlj *wrote: I hope this turns into a thread on "How I keep going" - there must be scores of pilots more excellent than I who can say more than me. I well remember that years ago when a visiting German pilot asked for advice on finding thermals in Arizona I told him to look above and downwind of cattle tanks. *These are known as stock ponds in other places. *His reaction, that I must be a complete idiot for suggesting that pools of water could trigger thermals, has made me cautious about offering that advice to anyone. *I hoped he landed out but I don't think he did. Andy Andy's observation is a secret well-known *to cross-country pilots in Arizona. *Sometimes the most ridiculously small and almost dry water holes will be the source of strong thermals. *My theory is that water holes inject enough moisture into the hot dry air to significantly increase its buoyancy. *We also have small hills consisting of black volcanic rock that are also good sources. *Dry river beds (called washes in the southwest US) also can be useful sources. Another issue with clouds here is that on fairly dry days the top of the lift is often a thousand feet or more below cloud base. *However, a strong thermal will often continue for a short time above the top of lift fueled by the extra heat released by condensation and eventually form a cumulus. *Once this short thermal pulse has decayed, the area immediately below the cloud then has no lift, although the original thermal may still be found a few thousand feet below. *I call these clouds "cumulus decoyus" - decoy cumulus! Mike Known in other parts of the world as "Cumulus no-liftus" Craig |
#14
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Where is the next thermal?
On Mon, 21 Sep 2009 15:28:09 -0700 (PDT), Andy
wrote: On Sep 21, 1:52*pm, danlj wrote: I hope this turns into a thread on "How I keep going" - there must be scores of pilots more excellent than I who can say more than me. I well remember that years ago when a visiting German pilot asked for advice on finding thermals in Arizona I told him to look above and downwind of cattle tanks. These are known as stock ponds in other places. His reaction, that I must be a complete idiot for suggesting that pools of water could trigger thermals, has made me cautious about offering that advice to anyone. I hoped he landed out but I don't think he did. Andy There was an article in S&G, a few years ago, about thermal origin and how to guess their location. It was under the title "Triggers and Feeders". Interesting reading about the wide areas that collect warmer air, and features on the ground that induce the bubbles to win adhesion and start soaring. An antenna, a pond, a building, a moving object etc, all are excellent triggers, but they're worth nothing without an adequate volume of warm air being supplied by the feeder area. Aldo Cernezzi |
#15
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Where is the next thermal?
On Sep 22, 7:03*pm, cernauta wrote:
On Mon, 21 Sep 2009 15:28:09 -0700 (PDT), Andy wrote: On Sep 21, 1:52*pm, danlj wrote: I hope this turns into a thread on "How I keep going" - there must be scores of pilots more excellent than I who can say more than me. I well remember that years ago when a visiting German pilot asked for advice on finding thermals in Arizona I told him to look above and downwind of cattle tanks. *These are known as stock ponds in other places. *His reaction, that I must be a complete idiot for suggesting that pools of water could trigger thermals, has made me cautious about offering that advice to anyone. *I hoped he landed out but I don't think he did. Andy There was an article in S&G, a few years ago, about thermal origin and how to guess their location. It was under the title "Triggers and Feeders". Interesting reading about the wide areas that collect warmer air, and features on the ground that induce the bubbles to win adhesion and start soaring. An antenna, a pond, a building, a moving object etc, all are excellent triggers, but they're worth nothing without an adequate volume of warm air being supplied by the feeder area. Aldo Cernezzi Many times in strong conditions (especially down low) there will a strong downdraft to be crossed before you hit that (thank you god) strong thermal. Bill Snead |
#16
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Where is the next thermal?
I've heard pilots say that the departure of an aircraft will kick off a
thermal from the runway. Worth watching if you are relatively low over the field and your timing is right to search it out. At 00:03 23 September 2009, cernauta wrote: On Mon, 21 Sep 2009 15:28:09 -0700 (PDT), Andy wrote: On Sep 21, 1:52*pm, danlj wrote: I hope this turns into a thread on "How I keep going" - there must be scores of pilots more excellent than I who can say more than me. I well remember that years ago when a visiting German pilot asked for advice on finding thermals in Arizona I told him to look above and downwind of cattle tanks. These are known as stock ponds in other places. His reaction, that I must be a complete idiot for suggesting that pools of water could trigger thermals, has made me cautious about offering that advice to anyone. I hoped he landed out but I don't think he did. Andy There was an article in S&G, a few years ago, about thermal origin and how to guess their location. It was under the title "Triggers and Feeders". Interesting reading about the wide areas that collect warmer air, and features on the ground that induce the bubbles to win adhesion and start soaring. An antenna, a pond, a building, a moving object etc, all are excellent triggers, but they're worth nothing without an adequate volume of warm air being supplied by the feeder area. Aldo Cernezzi |
#17
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Where is the next thermal?
On Wed, 23 Sep 2009 01:45:02 +0000, Nyal Williams wrote:
I've heard pilots say that the departure of an aircraft will kick off a thermal from the runway. Worth watching if you are relatively low over the field and your timing is right to search it out. Its well known in the free flight model flying world that in the right conditions a few people running about flapping T-shirts can kick off a thermal. I once made my own thermal just by running about circle towing an F1A class competition glider in sparse foot-high dry grass on calm early morning conditions. It wasn't strong though - just enough to make a model with a 0.3 m/s min sink speed climb slowly. -- martin@ | Martin Gregorie gregorie. | Essex, UK org | |
#18
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Where is the next thermal?
I think this rather depends on the degree of instability in the air. On
relatively stable days the usual thermal sources often don't seem to work. You need a large area to remain undisturbed for some time until enough hot air is available to give a decent thermal when triggered. Often things like towns and motorways don't work because there is too much trigger activity going on and only tiny weak thermals will form that go to no great height. Derek Copeland At 14:01 23 September 2009, Martin Gregorie wrote: On Wed, 23 Sep 2009 01:45:02 +0000, Nyal Williams wrote: I've heard pilots say that the departure of an aircraft will kick off a thermal from the runway. Worth watching if you are relatively low over the field and your timing is right to search it out. Its well known in the free flight model flying world that in the right conditions a few people running about flapping T-shirts can kick off a thermal. I once made my own thermal just by running about circle towing an F1A class competition glider in sparse foot-high dry grass on calm early morning conditions. It wasn't strong though - just enough to make a model with a 0.3 m/s min sink speed climb slowly. -- martin@ | Martin Gregorie gregorie. | Essex, UK org | |
#19
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Where is the next thermal?
On Sep 21, 7:09*pm, rlovinggood wrote:
Two items: 1. *Junkyards 2. *Radio transmission antennas. I can understand the junkyards. *It's a good "discontinuity" in the surrounding area and has the wrecked cars packed tightly together, more so than the typical parking lot. As for the antennas, we speculate it's not the antenna itself, but the ground they're on. *They are probably most likely on the highest spot around, even though it all looks quite flat to us. *And, we're talking about the 2,000' tall, cable stayed antennas and not the little cell phone towers. *But I guess any water tower and radio antennas are placed on the highest ground in the local area. Remember, Your Mileage May Vary... Ray Lovinggood Carrboro, North Carolina, USA Yes, mine varies. I've found those shorter cell phone towers to be reliable lift points when I'm lower. They act as a wick to dislodge the warm air from the ground, I think. Reichmann points out that the warm air at the surface has a surface tension that needs to be broken. He relates the point by describing a case of finding a thermal down low that was wicking from a roadside monument. At medium levels you can sometimes relate a lift source with its resulting cloud. At a contest a year and a half ago I was getting lowish (2000ft or so) and was flying over some shaded ground looking for a thermal. Ahead, I saw a large field in the sunlight that was being plowed. To my left and even with the field was a new and growing cu (downwind). I drew a mental line between the two and pulled up into the strongest thermal of the day (an honest 8kt climb to cloudbase). -- Matt |
#20
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Where is the next thermal?
On Sep 23, 1:35*pm, mattm wrote:
On Sep 21, 7:09*pm, rlovinggood wrote: Two items: 1. *Junkyards 2. *Radio transmission antennas. I can understand the junkyards. *It's a good "discontinuity" in the surrounding area and has the wrecked cars packed tightly together, more so than the typical parking lot. As for the antennas, we speculate it's not the antenna itself, but the ground they're on. *They are probably most likely on the highest spot around, even though it all looks quite flat to us. *And, we're talking about the 2,000' tall, cable stayed antennas and not the little cell phone towers. *But I guess any water tower and radio antennas are placed on the highest ground in the local area. Remember, Your Mileage May Vary... Ray Lovinggood Carrboro, North Carolina, USA Yes, mine varies. *I've found those shorter cell phone towers to be reliable lift points when I'm lower. *They act as a wick to dislodge the warm air from the ground, I think. *Reichmann points out that the warm air at the surface has a surface tension that needs to be broken. *He relates the point by describing a case of finding a thermal down low that was wicking from a roadside monument. At medium levels you can sometimes relate a lift source with its resulting cloud. *At a contest a year and a half ago I was getting lowish (2000ft or so) and was flying over some shaded ground looking for a thermal. *Ahead, I saw a large field in the sunlight that was being plowed. *To my left and even with the field was a new and growing cu (downwind). *I drew a mental line between the two and pulled up into the strongest thermal of the day (an honest 8kt climb to cloudbase). -- Matt High tension power lines act as triggers, and the dirt roads/gap in the trees where the towers are located are generators. IMO. Brad |
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