Dynamic Soaring of Thermals etc.
11-26-2012, 03:57 PM
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Dynamic Soaring of Thermals etc.
After printing and reading the info from Taras Kineciuk I now have a way to explain ds of a thermal more easily so that one will not think a slope is required.
Just think of Ds as pushing against the atmosphere opposite to its direction of motion which is what you actually do. The atmosphere does need motion. Thermal ds is hard to visulize and is confusing and since ds has only been discussed from a slope its even harder to understand. Its easy to get in a war of definitions of words. so to make it more fair at least all the thermal ds Ihave been doing is done by flying slightly outside of thermal and rentering and pushing down on the thermal abruptly. Ibet that sounds confusing pushing down? I wll just say positive gee or lift vector. When you make the atmosphere lose energy the glider gains it. This works in any way you can find it occuring. The (backside) in thermal ds is anywhere the thermal is not. Think of it as a slope titled 90 degrees.
In baseball the bat actually loses some energy when the ball collides with it. The ball gains the bats energy. When you think of this it makes it so much easier and leads to all kinds of possibilities.
I saw your post Mathews about flying in alternative conditions. You can talk to me about this. I have time.
I just got this analogy- think of a rubber ball falling onto a platform thats risiing and then
When the ball hits the rising platform the velocity of the platform will be added to the velocity of the balls' bounce, so it will bounce higher. than if it hit a non-moving surface.
Just think of Ds as pushing against the atmosphere opposite to its direction of motion which is what you actually do. The atmosphere does need motion. Thermal ds is hard to visulize and is confusing and since ds has only been discussed from a slope its even harder to understand. Its easy to get in a war of definitions of words. so to make it more fair at least all the thermal ds Ihave been doing is done by flying slightly outside of thermal and rentering and pushing down on the thermal abruptly. Ibet that sounds confusing pushing down? I wll just say positive gee or lift vector. When you make the atmosphere lose energy the glider gains it. This works in any way you can find it occuring. The (backside) in thermal ds is anywhere the thermal is not. Think of it as a slope titled 90 degrees.
In baseball the bat actually loses some energy when the ball collides with it. The ball gains the bats energy. When you think of this it makes it so much easier and leads to all kinds of possibilities.
I saw your post Mathews about flying in alternative conditions. You can talk to me about this. I have time.
I just got this analogy- think of a rubber ball falling onto a platform thats risiing and then
When the ball hits the rising platform the velocity of the platform will be added to the velocity of the balls' bounce, so it will bounce higher. than if it hit a non-moving surface.
12-04-2012, 02:12 PM
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RE: Dynamic Soaring of Thermals etc.
Correct: slope soaring and dynamic soaring are two totally different animals. Dynamic soaring extracts energy from a property of the air flow called curl, which is, unfortunately, a vector calculus concept.
But there is a fairly simple way to describe it. Visualize a creek with some lily pads floating in it that have broken loose from their roots and are moving along with the current. If the pads are rotating, the flow has curl. In general, the curl will vary from one value near the left bank, to zero at the centerline, to an opposite-sign value near the right bank which is another way of saying that the pads on the left rotate counterclockwise and those on the right, clockwise.
Air flow can be curled just as water flow can, and a sailplane can extract lift from that, even without any vertical air motion. If you analyze the process deeply enough, you'll come to a remarkably elegant conclusion: you will get the maximum climb rate by circling in a 55-degree bank, regardless of your wingspan, your airspeed, the value of the curl, or pretty much anything else!
In practice, the airflow is rarely either "curled without vertical motion" or "with vertical motion but no curl"; what you actually encounter is almost always a combination. Soaring birds do an impressive job of using slope and dynamic lift at the same time.
But there is a fairly simple way to describe it. Visualize a creek with some lily pads floating in it that have broken loose from their roots and are moving along with the current. If the pads are rotating, the flow has curl. In general, the curl will vary from one value near the left bank, to zero at the centerline, to an opposite-sign value near the right bank which is another way of saying that the pads on the left rotate counterclockwise and those on the right, clockwise.
Air flow can be curled just as water flow can, and a sailplane can extract lift from that, even without any vertical air motion. If you analyze the process deeply enough, you'll come to a remarkably elegant conclusion: you will get the maximum climb rate by circling in a 55-degree bank, regardless of your wingspan, your airspeed, the value of the curl, or pretty much anything else!
In practice, the airflow is rarely either "curled without vertical motion" or "with vertical motion but no curl"; what you actually encounter is almost always a combination. Soaring birds do an impressive job of using slope and dynamic lift at the same time.
12-04-2012, 04:18 PM
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RE: Dynamic Soaring of Thermals etc.
ORIGINAL: abelard
Correct: slope soaring and dynamic soaring are two totally different animals. Dynamic soaring extracts energy from a property of the air flow called curl, which is, unfortunately, a vector calculus concept.
But there is a fairly simple way to describe it. Visualize a creek with some lily pads floating in it that have broken loose from their roots and are moving along with the current. If the pads are rotating, the flow has curl. In general, the curl will vary from one value near the left bank, to zero at the centerline, to an opposite-sign value near the right bank which is another way of saying that the pads on the left rotate counterclockwise and those on the right, clockwise.
Air flow can be curled just as water flow can, and a sailplane can extract lift from that, even without any vertical air motion. If you analyze the process deeply enough, you'll come to a remarkably elegant conclusion: you will get the maximum climb rate by circling in a 55-degree bank, regardless of your wingspan, your airspeed, the value of the curl, or pretty much anything else!
In practice, the airflow is rarely either "curled without vertical motion" or "with vertical motion but no curl"; what you actually encounter is almost always a combination. Soaring birds do an impressive job of using slope and dynamic lift at the same time.
Correct: slope soaring and dynamic soaring are two totally different animals. Dynamic soaring extracts energy from a property of the air flow called curl, which is, unfortunately, a vector calculus concept.
But there is a fairly simple way to describe it. Visualize a creek with some lily pads floating in it that have broken loose from their roots and are moving along with the current. If the pads are rotating, the flow has curl. In general, the curl will vary from one value near the left bank, to zero at the centerline, to an opposite-sign value near the right bank which is another way of saying that the pads on the left rotate counterclockwise and those on the right, clockwise.
Air flow can be curled just as water flow can, and a sailplane can extract lift from that, even without any vertical air motion. If you analyze the process deeply enough, you'll come to a remarkably elegant conclusion: you will get the maximum climb rate by circling in a 55-degree bank, regardless of your wingspan, your airspeed, the value of the curl, or pretty much anything else!
In practice, the airflow is rarely either "curled without vertical motion" or "with vertical motion but no curl"; what you actually encounter is almost always a combination. Soaring birds do an impressive job of using slope and dynamic lift at the same time.
12-05-2012, 11:27 AM
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RE: Dynamic Soaring of Thermals etc.
If the flow is purely horizontal with curl, everything is constant: the glider will climb at the same rate everywhere in the circle; you're always using the curl. If there's vertical motion, and that motion varies within the size of your circle, obviously the climb rate will vary as you go round.
12-08-2012, 03:47 PM
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RE: Dynamic Soaring of Thermals etc.
I see what you're saying. But most folks would have trouble identifying and marking a thermal boundry accurately enough to actually dynamic soar a thermal. If you've managed it now and then I comend your keen skills.
What sort of speeds do you think you've managed by doing that?
If we consider dynamic soaring as anything where the aircraft experiences a shift in wind velocity or direction and gains energy from such a shift then it opens up the meaning of dynamic soaring. It's not just about playing the shear line on a slope site. It can also be the case when pushing in and out of a thermal just as you're suggesting or even flying on a blustery day where there are big shifts in the wind speed and direction even on a flat field. The key is being able to gain energy as speed or height from the model transitioning from the apparent relative wind direction and velocity changes as the aircraft experences the changes.
We can "force" the changes to occur such as turning/looping through the shear plane on a slope between the front and back areas. We can also force the changes by flying into and out of a strong thermal as you're describing. Or we can fly in a manner that we simply bump into them as they pass the model and fly the transitions to gain energy from the shifts.
I suspect it's fair to say that what puts the "dynamic" into such flying is that the aircraft is being flown where it can see frequent changes in the apparent wind speed and direction.
What sort of speeds do you think you've managed by doing that?
If we consider dynamic soaring as anything where the aircraft experiences a shift in wind velocity or direction and gains energy from such a shift then it opens up the meaning of dynamic soaring. It's not just about playing the shear line on a slope site. It can also be the case when pushing in and out of a thermal just as you're suggesting or even flying on a blustery day where there are big shifts in the wind speed and direction even on a flat field. The key is being able to gain energy as speed or height from the model transitioning from the apparent relative wind direction and velocity changes as the aircraft experences the changes.
We can "force" the changes to occur such as turning/looping through the shear plane on a slope between the front and back areas. We can also force the changes by flying into and out of a strong thermal as you're describing. Or we can fly in a manner that we simply bump into them as they pass the model and fly the transitions to gain energy from the shifts.
I suspect it's fair to say that what puts the "dynamic" into such flying is that the aircraft is being flown where it can see frequent changes in the apparent wind speed and direction.
