I think this is the same case of explaining why planes fly. There's no unique explanation or, in other words, there are two possible and physical explanations that are equally right.Faxie wrote: ↑Wed Jul 28, 2021 6:14 amIt started with the mention of the coanda effect. Well, I thought, very good someone finally seems to get it. And then it went downhill very fast unfortunately...
Coanda is a result of Newton's laws and those laws works on both sides of the kite.
2 Good papers that mention coanda:
https://user.uni-frankfurt.de/~weltner/ ... ternet.pdf
http://www.prirodopolis.hr/daily_phy/pd ... 20hork.pdf
A kite 'pulls' itself forward because it's a tethered object (and that's why it cannot be considered the same as a regular wing). It doesn't push itself forward against it's own generated turbulence. Turbulence is a result of flow separation, contributing to drag, and drag pulls the kite backwards. Ever heard of backstalling? Gee I wonder how that happens?
The aoa and window parts aren't completely right either, and so is the wakeboard comparison. A boat doesn't change it's speed, force and direction because of the change in speed, force and direction of the wakeboarder. Even if you're the Hulk and can brake to a standstill, the boat will keep going forward (though will circle around you offcourse). A kite is limited by the window, which is a direct dynamic (apparent) result of the actions of the kiter (or basically, the tether).
About your last paragraph... What a wonderful sport!!rnelias wrote: ↑Wed Jul 28, 2021 7:05 pmI think this is the same case of explaining why planes fly. There's no unique explanation or, in other words, there are two possible and physical explanations that are equally right.Faxie wrote: ↑Wed Jul 28, 2021 6:14 amIt started with the mention of the coanda effect. Well, I thought, very good someone finally seems to get it. And then it went downhill very fast unfortunately...
Coanda is a result of Newton's laws and those laws works on both sides of the kite.
2 Good papers that mention coanda:
https://user.uni-frankfurt.de/~weltner/ ... ternet.pdf
http://www.prirodopolis.hr/daily_phy/pd ... 20hork.pdf
A kite 'pulls' itself forward because it's a tethered object (and that's why it cannot be considered the same as a regular wing). It doesn't push itself forward against it's own generated turbulence. Turbulence is a result of flow separation, contributing to drag, and drag pulls the kite backwards. Ever heard of backstalling? Gee I wonder how that happens?
The aoa and window parts aren't completely right either, and so is the wakeboard comparison. A boat doesn't change it's speed, force and direction because of the change in speed, force and direction of the wakeboarder. Even if you're the Hulk and can brake to a standstill, the boat will keep going forward (though will circle around you offcourse). A kite is limited by the window, which is a direct dynamic (apparent) result of the actions of the kiter (or basically, the tether).
Here's a good reference on this subject.
https://www.scientificamerican.com/arti ... n-the-air/
Bernoulli principle and/or third Newtons law, both are right... (and the Navier-Stokes equations come from Newton's second law too ...) (*)
Moreover, depending on the format of the kite, it'll have a completely different behavior acting more like a true wing or, in the opposite side, as a simple "bag or air". High aspect ratio kites, like racing foil kites, or more modestly, big air 5-struct kites, can lift us vertically with no big effort and these kites behaves more like a true wing. However, we also have to consider kites with more C-shaped curves like the kites used on wakestyle or surf/foil kites. These kites behave more like a "bag of air" pulling us downwind. They don't fly like "pure wings" and produce more power when are flown deeper in the wind window.
The beauty on this subject is that designers can play with the kite's design to extract more of one side and specialize the kite when the market requires.
Kites when combined with hydrofoils are even more impressive as we can understand that there are two wings "fighting" in different physical enviroments. The kite in the air and the hydrofoil in the water while the rider is taking advantage of this physical equilibrium.
Fully agree and I must say that I do not agree with the "restricted point of view of the article" ; of course simply redirecting the airflow is a major contributor, we cannot forget that, and even if you do not consider Bernoulli effect by using a flat profile for example (no difference fo curvature intrados vs extrado : indeed, even a simple rigid thin flat sheet can produce lift if it has an angle of attack, just by redirecting the airflow along the Angle of attack) : air changes its direction, so the counter reaction of this inertia change is a opposite lift on the flat profile) ; some very simple hydrofoils or children kite work like that with flat profiles ... So it is a combination of many physics like said above, with dirreretn impact if you talk about a race kite or a nasawing or a spinnacker...rnelias wrote: ↑Wed Jul 28, 2021 7:05 pm
Bernoulli principle and/or third Newtons law, both are right... (and the Navier-Stokes equations come from Newton's second law too ...) (*)
Moreover, depending on the format of the kite, it'll have a completely different behavior acting more like a true wing or, in the opposite side, as a simple "bag or air". High aspect ratio kites, like racing foil kites, or more modestly, big air 5-struct kites, can lift us vertically with no big effort and these kites behaves more like a true wing. However, we also have to consider kites with more C-shaped curves like the kites used on wakestyle or surf/foil kites. These kites behave more like a "bag of air" pulling us downwind. They don't fly like "pure wings" and produce more power when are flown deeper in the wind window.
The beauty on this subject is that designers can play with the kite's design to extract more of one side and specialize the kite when the market requires.
Kites when combined with hydrofoils are even more impressive as we can understand that there are two wings "fighting" in different physical enviroments. The kite in the air and the hydrofoil in the water while the rider is taking advantage of this physical equilibrium.
Curvature of a foil section allows a time (delta) component for the change of direction of air molecules.Regis-de-giens wrote: ↑Fri Jul 30, 2021 3:04 pm...... of course simply redirecting the airflow is a major contributor, we cannot forget that, and even if you do not consider Bernoulli effect by using a flat profile for example (no difference fo curvature intrados vs extrado : indeed, even a simple rigid thin flat sheet can produce lift if it has an angle of attack, just by redirecting the airflow along the Angle of attack) :
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