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#1
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Where is the next thermal?
I am writing this to ask experienced soaring pilots to correct me
where you have acquired different wisdom, or your local conditions are different, or where you have something more to add. 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. More than 20 years ago, before I had become able to pursue soaring (as distinguished from gliding), a letter to the editor appeared in Soaring Magazine. A SE-WI hang-gliding pilot who'd done a lot of self- taught XC soaring, innocently thought that SSA members might have a lot more wisdom that he, so he asked for clues on how to find thermals. He never got a response that was printed in the magazine... He did tell the one thing he knew about finding thermals: "The best lift is at the most downwind corner of the field." This, in my own experience, is the single most important clue on where to go when scratching low, here over the prairies. Identifying what is "the field", where the wind's coming from, and what's "a corner" have sometimes been challenging, and figuring out just how small hills and valleys will affect the thermals is always interesting (hills tend to help, valleys tend to channel them - flying downwind up a valley above ridgetop is usually a route to a save). I've also noticed that any isolated sorta-bare hill or rock pile on flat ground is a pretty reliable source... On the negative side, being anywhere downwind of any lake wider than about a mile, or wet river flood plain, is definitely associated with a lack of organized thermals, sometimes for miles. Forests are bad, but the clearings in them are good. Swamps in the prairie are often bad (wet) but in the woods often create boomers due to the differential, and moist air is buoyant. I am not very good at identifying the best field when they all look good (spring planting or fall harvest). On the first cold day after a warm spell in the fall, some fields generate thermals on overcast days: the best seem to be cut bean fields, covered with a thin layer of stems and leaves. Early in the day, thermal sources tend to be small (a single field or parking lot) and late in the day, they tend to be very large (e.g., a 3-10 mile-diameter prairie). And at the beginning of the day, all clouds have lift (of quite variable strength), mid-day, as few as 20% do, and late in the day, the appearance of the cloud is a reliable indicator of whether it's "working." When high, the corollary to the field is of course the flat cu: the first place to look for the thermal is at the most upwind part of the cloud. Although again, what's a "cloud", where the wind's coming from, and the direction of the wind above cloudbase all affect what will be found. Clouds with flat bases are better that clouds with fuzzy bases, except that a new wisp always has something, and an "old" flat cloud may be dying. Clouds with enthusiastic tops are sucking air, and under these, the lift is usually under the tower (useful when aiming from a distance) and there's often a dimple in the bottom where the suction is greatest. I was once told that streamers usually indicate condensing lift, but I've found this usually wrong -- except when the thermal is unusually humid. Clouds sometimes are lined up. My experience is that the streets are fake (but not necessarily useless) if the surface wind is less than 10 kt, and usually real above that; but that all streets end. The hardest time for me is when I'm sort of midway between cloud and ground. Do I fly under the best part of the cloud and look up? Or do I fly toward the thermal source? Or, how can I reliably identify a good intermediate point? In this regard, I've found that thermals are curved, sometimes strongly (if imagined in "section"). This can be seen with swamp fires, where the smoke skims along the ground for awhile, then begins to rise in a great slow curve to the small cu created by the humidity released from the ground by the fire's heat. This makes physical sense, when one stops to think about it, for the wind first whisks the thermal bubble along horizontally (at, say, 10 mph = 900 ft/min). The warmed air must accelerate; this rate of acceleration depends on the buoyancy of the thermal relative to the lapse rate. If it's a boomer, say 900 ft/min, then the angle will go from nil to 45 degrees as it accelerates, and this feels almost vertical. But down low, below about 1500 ft agl, the clouds are sometimes more a distraction than a help because of this. The curvature of thermals, I think, is a special mystery when trying to fly xwind on a blue day. I, at least, often feel mystified. More topics, about which I can't say much: Staying alive late in the day (e.g., "there's zero-sink over freeways") Identifying mountain thermals "Good terrain" in deserts sea-breeze and dry-front lift other... |
#2
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Where is the next thermal?
On Sep 21, 1:52*pm, danlj wrote:
I am writing this to ask experienced soaring pilots to correct me where you have acquired different wisdom, or your local conditions are different, or where you have something more to add. 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. More than 20 years ago, before I had become able to pursue soaring (as distinguished from gliding), a letter to the editor appeared in Soaring Magazine. A SE-WI hang-gliding pilot who'd done a lot of self- taught XC soaring, innocently thought that SSA members might have a lot more wisdom that he, so he asked for clues on how to find thermals. He never got a response that was printed in the magazine... He did tell the one thing he knew about finding thermals: "The best lift is at the most downwind corner of the field." This, in my own experience, is the single most important clue on where to go when scratching low, here over the prairies. *Identifying what is "the field", where the wind's coming from, and what's "a corner" have sometimes been challenging, and figuring out just how small hills and valleys will affect the thermals is always interesting (hills tend to help, valleys tend to channel them - flying downwind up a valley above ridgetop is usually a route to a save). I've also noticed that any isolated sorta-bare hill or rock pile on flat ground is a pretty reliable source... On the negative side, being anywhere downwind of any lake wider than about a mile, or wet river flood plain, is definitely associated with a lack of organized thermals, sometimes for miles. Forests are bad, but the clearings in them are good. Swamps in the prairie are often bad (wet) but in the woods often create boomers due to the differential, and moist air is buoyant. I am not very good at identifying the best field when they all look good (spring planting or fall harvest). On the first cold day after a warm spell in the fall, some fields generate thermals on overcast days: the best seem to be cut bean fields, covered with a thin layer of stems and leaves. Early in the day, thermal sources tend to be small (a single field or parking lot) and late in the day, they tend to be very large (e.g., a 3-10 mile-diameter prairie). And at the beginning of the day, all clouds have lift (of quite variable strength), mid-day, as few as 20% do, and late in the day, the appearance of the cloud is a reliable indicator of whether it's "working." When high, the corollary to the field is of course the flat cu: the first place to look for the thermal is at the most upwind part of the cloud. Although again, what's a "cloud", where the wind's coming from, and the direction of the wind above cloudbase all affect what will be found. Clouds with flat bases are better that clouds with fuzzy bases, except that a new wisp always has something, and an "old" flat cloud may be dying. Clouds with enthusiastic tops are sucking air, and under these, the lift is usually under the tower (useful when aiming from a distance) and there's often a dimple in the bottom where the suction is greatest. I was once told that streamers usually indicate condensing lift, but I've found this usually wrong -- except when the thermal is unusually humid. Clouds sometimes are lined up. My experience is that the streets are fake (but not necessarily useless) if the surface wind is less than 10 kt, and usually real above that; but that all streets end. The hardest time for me is when I'm sort of midway between cloud and ground. Do I fly under the best part of the cloud and look up? Or do I fly toward the thermal source? Or, how can I reliably identify a good intermediate point? In this regard, I've found that thermals are curved, sometimes strongly (if imagined in "section"). This can be seen with swamp fires, where the smoke skims along the ground for awhile, then begins to rise in a great slow curve to the small cu created by the humidity released from the ground by the fire's heat. This makes physical sense, when one stops to think about it, for the wind first whisks the thermal bubble along horizontally (at, say, 10 mph = 900 ft/min). The warmed air must accelerate; this rate of acceleration depends on the buoyancy of the thermal relative to the lapse rate. If it's a boomer, say 900 ft/min, then the angle will go from nil to 45 degrees as it accelerates, and this feels almost vertical. But down low, below about 1500 ft agl, the clouds are sometimes more a distraction than a help because of this. *The curvature of thermals, I think, is a special mystery when trying to fly xwind on a blue day. I, at least, often feel mystified. More topics, about which I can't say much: Staying alive late in the day (e.g., "there's zero-sink over freeways") Identifying mountain thermals "Good terrain" in deserts sea-breeze and dry-front lift other... Danlj A very nice collection of ideas for finding thermals. Many of the same Ideas that I have noticed and shared with students. They work better in farmland and wooded areas than desert as the triggers are less distinct in the dessert and more of the surface are is being heated to the same temperature. Regarding the "downwind corner", I also note that where the ground surface changes; dry to wet, low to high, plowed to growing. At each of these areas especially if you can identify that the downwind surface is colder or denser, there will be the necessary upward push to start a thermal. I describe them as "discontinuities" in the surface. They form an edge, if you will, that can trigger the thermal. Thanks for the list. Mike |
#3
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Where is the next thermal?
A bare field just downwind of a patch of trees has time to heat up more
owing to the windbreak and it can kick off a thermal sometimes down lower. Also, wooded areas serve well late in the day. Surrounding open land will cool off more quickly and then the woods will begin to give up its heat in a soft thermal that won't go very high, but can serve to hang on for a bit and as a place from which to jump to the next woods patch while trying to get home. Not an expert by r.a.s. standards. At 21:13 21 September 2009, Mike Bamberg wrote: On Sep 21, 1:52=A0pm, danlj wrote: I am writing this to ask experienced soaring pilots to correct me where you have acquired different wisdom, or your local conditions are different, or where you have something more to add. 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. More than 20 years ago, before I had become able to pursue soaring (as distinguished from gliding), a letter to the editor appeared in Soaring Magazine. A SE-WI hang-gliding pilot who'd done a lot of self- taught XC soaring, innocently thought that SSA members might have a lot more wisdom that he, so he asked for clues on how to find thermals. He never got a response that was printed in the magazine... He did tell the one thing he knew about finding thermals: "The best lift is at the most downwind corner of the field." This, in my own experience, is the single most important clue on where to go when scratching low, here over the prairies. =A0Identifying what is "the field", where the wind's coming from, and what's "a corner" have sometimes been challenging, and figuring out just how small hills and valleys will affect the thermals is always interesting (hills tend to help, valleys tend to channel them - flying downwind up a valley above ridgetop is usually a route to a save). I've also noticed that any isolated sorta-bare hill or rock pile on flat ground is a pretty reliable source... On the negative side, being anywhere downwind of any lake wider than about a mile, or wet river flood plain, is definitely associated with a lack of organized thermals, sometimes for miles. Forests are bad, but the clearings in them are good. Swamps in the prairie are often bad (wet) but in the woods often create boomers due to the differential, and moist air is buoyant. I am not very good at identifying the best field when they all look good (spring planting or fall harvest). On the first cold day after a warm spell in the fall, some fields generate thermals on overcast days: the best seem to be cut bean fields, covered with a thin layer of stems and leaves. Early in the day, thermal sources tend to be small (a single field or parking lot) and late in the day, they tend to be very large (e.g., a 3-10 mile-diameter prairie). And at the beginning of the day, all clouds have lift (of quite variable strength), mid-day, as few as 20% do, and late in the day, the appearance of the cloud is a reliable indicator of whether it's "working." When high, the corollary to the field is of course the flat cu: the first place to look for the thermal is at the most upwind part of the cloud. Although again, what's a "cloud", where the wind's coming from, and the direction of the wind above cloudbase all affect what will be found. Clouds with flat bases are better that clouds with fuzzy bases, except that a new wisp always has something, and an "old" flat cloud may be dying. Clouds with enthusiastic tops are sucking air, and under these, the lift is usually under the tower (useful when aiming from a distance) and there's often a dimple in the bottom where the suction is greatest. I was once told that streamers usually indicate condensing lift, but I've found this usually wrong -- except when the thermal is unusually humid. Clouds sometimes are lined up. My experience is that the streets are fake (but not necessarily useless) if the surface wind is less than 10 kt, and usually real above that; but that all streets end. The hardest time for me is when I'm sort of midway between cloud and ground. Do I fly under the best part of the cloud and look up? Or do I fly toward the thermal source? Or, how can I reliably identify a good intermediate point? In this regard, I've found that thermals are curved, sometimes strongly (if imagined in "section"). This can be seen with swamp fires, where the smoke skims along the ground for awhile, then begins to rise in a great slow curve to the small cu created by the humidity released from the ground by the fire's heat. This makes physical sense, when one stops to think about it, for the wind first whisks the thermal bubble along horizontally (at, say, 10 mph =3D 900 ft/min). The warmed air must accelerate; this rate of acceleration depends on the buoyancy of the thermal relative to the lapse rate. If it's a boomer, say 900 ft/min, then the angle will go from nil to 45 degrees as it accelerates, and this feels almost vertical. But down low, below about 1500 ft agl, the clouds are sometimes more a distraction than a help because of this. =A0The curvature of thermals, I think, is a special mystery when trying to fly xwind on a blue day. I, at least, often feel mystified. More topics, about which I can't say much: Staying alive late in the day (e.g., "there's zero-sink over freeways") Identifying mountain thermals "Good terrain" in deserts sea-breeze and dry-front lift other... Danlj A very nice collection of ideas for finding thermals. Many of the same Ideas that I have noticed and shared with students. They work better in farmland and wooded areas than desert as the triggers are less distinct in the dessert and more of the surface are is being heated to the same temperature. Regarding the "downwind corner", I also note that where the ground surface changes; dry to wet, low to high, plowed to growing. At each of these areas especially if you can identify that the downwind surface is colder or denser, there will be the necessary upward push to start a thermal. I describe them as "discontinuities" in the surface. They form an edge, if you will, that can trigger the thermal. Thanks for the list. Mike |
#4
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Where is the next thermal?
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 |
#5
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Where is the next thermal?
I've noticed that there seems to be a time in the afternoon when the
lift gets "soft" and previously reliable clouds become much less reliable. Then, after an hour or so, the lift seems to pick up again, not usually as strong but good enough to get home. My totally uneducated guess is that at some point, the reserve of lift that is breaking loose and forming thermals gets exhausted and isn't replenished fast enough, so it takes a while to build up again and start making reliable thermals. This is really noticable where I often fly in Illinois, where you have to slow down and be real careful not to get too low mid afternoon, even though the day still looks great with cu's all over the place - around 2 to 3 in the afternoon it gets real soft and you have to slow down and stay high and wait for the lift to cycle back on. Then you can stay up till the sun goes down! Kirk 66 |
#6
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Where is the next thermal?
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 |
#7
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Where is the next thermal?
I have very good luck going right over the center of a town.
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#8
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Where is the next thermal?
Downwind at the edge of the dry lake.
Dry hot air moving across the lake bed get triggered to release and rise when encountering the scrub. On an open desert floor, look for darker areas. The darker areas are most likely elevated hard rock that is hotter than the surrounding sand and dirt. I have also found thermals coming up from broad open "dry washes", the exposed rock in the dry wash gets hotter than the surrounding soils. BT "Mike Bamberg" wrote in message ... On Sep 21, 1:52 pm, danlj wrote: I am writing this to ask experienced soaring pilots to correct me where you have acquired different wisdom, or your local conditions are different, or where you have something more to add. 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. More than 20 years ago, before I had become able to pursue soaring (as distinguished from gliding), a letter to the editor appeared in Soaring Magazine. A SE-WI hang-gliding pilot who'd done a lot of self- taught XC soaring, innocently thought that SSA members might have a lot more wisdom that he, so he asked for clues on how to find thermals. He never got a response that was printed in the magazine... He did tell the one thing he knew about finding thermals: "The best lift is at the most downwind corner of the field." This, in my own experience, is the single most important clue on where to go when scratching low, here over the prairies. Identifying what is "the field", where the wind's coming from, and what's "a corner" have sometimes been challenging, and figuring out just how small hills and valleys will affect the thermals is always interesting (hills tend to help, valleys tend to channel them - flying downwind up a valley above ridgetop is usually a route to a save). I've also noticed that any isolated sorta-bare hill or rock pile on flat ground is a pretty reliable source... On the negative side, being anywhere downwind of any lake wider than about a mile, or wet river flood plain, is definitely associated with a lack of organized thermals, sometimes for miles. Forests are bad, but the clearings in them are good. Swamps in the prairie are often bad (wet) but in the woods often create boomers due to the differential, and moist air is buoyant. I am not very good at identifying the best field when they all look good (spring planting or fall harvest). On the first cold day after a warm spell in the fall, some fields generate thermals on overcast days: the best seem to be cut bean fields, covered with a thin layer of stems and leaves. Early in the day, thermal sources tend to be small (a single field or parking lot) and late in the day, they tend to be very large (e.g., a 3-10 mile-diameter prairie). And at the beginning of the day, all clouds have lift (of quite variable strength), mid-day, as few as 20% do, and late in the day, the appearance of the cloud is a reliable indicator of whether it's "working." When high, the corollary to the field is of course the flat cu: the first place to look for the thermal is at the most upwind part of the cloud. Although again, what's a "cloud", where the wind's coming from, and the direction of the wind above cloudbase all affect what will be found. Clouds with flat bases are better that clouds with fuzzy bases, except that a new wisp always has something, and an "old" flat cloud may be dying. Clouds with enthusiastic tops are sucking air, and under these, the lift is usually under the tower (useful when aiming from a distance) and there's often a dimple in the bottom where the suction is greatest. I was once told that streamers usually indicate condensing lift, but I've found this usually wrong -- except when the thermal is unusually humid. Clouds sometimes are lined up. My experience is that the streets are fake (but not necessarily useless) if the surface wind is less than 10 kt, and usually real above that; but that all streets end. The hardest time for me is when I'm sort of midway between cloud and ground. Do I fly under the best part of the cloud and look up? Or do I fly toward the thermal source? Or, how can I reliably identify a good intermediate point? In this regard, I've found that thermals are curved, sometimes strongly (if imagined in "section"). This can be seen with swamp fires, where the smoke skims along the ground for awhile, then begins to rise in a great slow curve to the small cu created by the humidity released from the ground by the fire's heat. This makes physical sense, when one stops to think about it, for the wind first whisks the thermal bubble along horizontally (at, say, 10 mph = 900 ft/min). The warmed air must accelerate; this rate of acceleration depends on the buoyancy of the thermal relative to the lapse rate. If it's a boomer, say 900 ft/min, then the angle will go from nil to 45 degrees as it accelerates, and this feels almost vertical. But down low, below about 1500 ft agl, the clouds are sometimes more a distraction than a help because of this. The curvature of thermals, I think, is a special mystery when trying to fly xwind on a blue day. I, at least, often feel mystified. More topics, about which I can't say much: Staying alive late in the day (e.g., "there's zero-sink over freeways") Identifying mountain thermals "Good terrain" in deserts sea-breeze and dry-front lift other... Danlj A very nice collection of ideas for finding thermals. Many of the same Ideas that I have noticed and shared with students. They work better in farmland and wooded areas than desert as the triggers are less distinct in the dessert and more of the surface are is being heated to the same temperature. Regarding the "downwind corner", I also note that where the ground surface changes; dry to wet, low to high, plowed to growing. At each of these areas especially if you can identify that the downwind surface is colder or denser, there will be the necessary upward push to start a thermal. I describe them as "discontinuities" in the surface. They form an edge, if you will, that can trigger the thermal. Thanks for the list. Mike |
#9
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Where is the next thermal?
Flying in the Midwest farm country of the USA I find the vast majority
of thermals by simply blundering into them blindly. Below 1500AGL ground clues MAY help you find lift but just as likely not. In rocky mountainous terrain it's a different story. Determine what altitude is half way to cloudbase (if there are clouds); Below that ignore the clouds and just go, above that the clouds MAY help you find lift. Real cloudstreets DO exist as do lift streets with no clouds. Keep an open mind at all times. Many people fly too slow in sink or even turn in sink trying to decide what to do. Even at 800agl if the vario says 500 or 1000 down go FAST and go straight. You are much more likely to hit a thermal on your way to your landing field than if you fly around maneuvering slow. Fly SLOW in lift or zero sink. Pull back on the stick to min sink and do it immediately. Many people turn too shallow and too late in thermals. Circle just about as tight as you can fly slow in most thermals for the best climb rate. Keep a positive attitude. Keep a couple landing fields in sight but keep a positive attitude. Many XC flights have been saved on downwind. Once you turn base give it up. Hear the theme to Star Trek in your mind and boldly go where no one has gone before. |
#10
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Where is the next thermal?
Here is my methodology, most of which is found in Reichmann's
excellent book. 1. Develop testable 3-D models of the lift in your mind, based on topography, wind, sun aspect and previous experience. This is my version of "strolling along the ground to find where it is hot" in Reichmann's definitive text. 2. Test the model by putting the glider in what you hypothesize as the best energy lines. 3. Fly as precisely and efficiently as you can and in an direct correlation to the intensity of lift/sink/turbulence: Smooth and easy inputs in light, smooth lift. Firm and aggressive when it is rock-and rolling. The flight paths of world-class pilots can appear as though they are drunk or very sloppy as they weave about. This is in direct opposition to wings lifting and can be used to locate in featureless, cloudless terrain. 3. Adjust your mental image and flight path based on test results and observation of other ships, birds, dust, etc. I believe AJ Smith and/ or Dick Schreder said that 90% of what you need to know is outside the cockpit and if you have not made a decision in the last 5 minutes, you are not working hard enough. Electron Slingers allow you to direct your attention and energy where it matters: OUTSIDE THE COCKPIT. A glance at the moving map periodically is all that is required to affirm your location and that you have suitable fields in a reasonable glide, how you are doing on task and what you need for final glide. 3. Repeat this decision-action loop every 1/2 hour or so based on changing wind direction and intensity, sun aspect, and terrain and what is 20-50 miles down the road. I would also echo what others have said: When close to clouds, use them as the primary reference. And not just "sort of under a cloud". You need to determine which side of the cloud and what cloud phase is optimal and what height below base. Target and test the clouds you select and adjust your selection process. As one gets lower, lift hunting is more and more attached to the terrain + wind + sun aspect. Finally, be mentally Tough and never quit "soaring" until you commit to landing. As someone said previously, many flights have been "sucked off the ground", mostly due to the pilot's persistence and willingness to fight until a safe landing is inevitably necessary. "Giving up" is very seductive and absolutely ensures you will land. Both of these behaviors are self-reinforcing; both become easier with repetition. "Grinding it out" is where our hang glider brothers really excel. The paradoxical situation we find ourselves in when low and facing an off-field landing is one of the many things I find interesting in X-C soaring. Just when we are under maximum stress and with minimal options, we need to be at our absolute technical best and most creative. Gotta love it! |
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