Regarding turbulence, I'm not a meteorologist, but from a paragliding perspective; I'd agree the primary division is between 'ground obstacle induced', and prevailing air 'stability'. Whilst both are affected by the air-mass characteristics the ground obstacle impact is, of course, easier to predict. Turbulence within the air-mass itself is primarily caused, as you suggest, by the mixing of different air. Normally this is due to differing layers at height, and is crucial to distance paragliding as it is necessary to find warm 'thermals' rising thru' colder air in order to gain altitude. Naturally as warm area rises then colder air falls down to equate the pressures, and this the basic cause of turbulent gusts. On the ground you can notice the wind direction of these can be very different to the prevailing breeze. This much is pretty straightforward and explains, for example. why inland winds are almost universally more difficult to use than more laminar 'sea breezes'. (Coastal Cliff soaring a glider in such conditions can be almost 'hands off'). The more subtle point is that some days the 'edges' of thermals are relatively smooth transitions , whilst on other days they can be seriously turbulent (leading to various 'collapses' of the wing). Apart from differing windspeed gradients this is normally also explained by pressure and humidity impacts. Dry high pressure days can be expected to be more turbulent, which is explained as being due to the 'bullet' nature of thermals on such days.
We definitely have experience with thermal winds shutting off - it seems that they get quite turbulent right before it happens. Thanks for the explanation :)
As always: clear, factual and well researched info. Thx Ourkitelife ! Now we need a device that blends all these effects together to tell you whether to go out and which kite to use.
honestly, I think one of the most addicting things about kiting is that you just never know how the session is going to turn out. So the solution you just go kite regardless
Great info as always. You can add 1 more and that would be water conditions. I find flat water is easy on the kite, where as riding ocean with a lot of current swells and breaks takes almost 2 kite sizes bigger just to ride.
Makes sense though, right? Denser air has more power. Humid air is less dense, tends to float up. Clouds float high in the sky on top of denser less humid air below.
Turbulence includes a vertical component. Close to the ground the might happen do to high winds speed shear just above the kitsters. Say if there are 80 knot winds at 800’ to 1000’ and 15 knots at the surface, that would creat plenty of eddies that would roll over each other and certainly include vertical velocities anywhere in the column. Gusty describes just describes variable winds speed over short time periods. It might include a vertical component but this not measured in reported wind speeds.
Great video, and something I've thought about a lot - especially the laminar vs turbulent flow and just how significant of an effect it can have on kite power. I ride almost exclusively on foil kites, and spend a lot of time on Lake McConaughy, Nebraska in the summer. At that lake, there is a very predictable morning wind that feels quite strong, but once you get out, it has hardly any power. In the afternoon the winds speeds can be significantly lower and yet surprisingly provide much more power. I've come to call the morning wind "holey", and the afternoon wind "plump", or "buoyant". I've come to basically the exact same conclusion you have: in the morning there is a lot of thermal mixing going on, making the flow more turbulent, whereas in the afternoon the thermals have steadied out making the winds more laminar. Aerodynamically speaking, I believe the reason this has such a significant impact on kite power is the following: in the gustier, more turbulent flow, I don't believe the air has the ability to fully attach and flow the full chord of the wing before it gets disrupted. This I'm guessing is causing premature flow separation on the topside of the wing near the trailing edge, kind of similar to what happens when a wing starts to stall. This means your wing is flying very inefficiently with a modified airfoil/airflow shape that looks nothing like it was designed to be; i.e low lift/high drag or low L/D ratio. In a nice laminar wind, however, the wind/air will stay attached the entire chord-length, just like the designer intended - and your kite performs like a dream - as it was intended. Too bad those laminar days are so few and far between for us inland kiters :) What would be really fun is to take a kite and tape a bunch of small pieces of thread across the entire wing (or at least a wing chord section) like you might have seen in wind tunnel tests, and then somehow get a video of the top surface in the different types of air. I bet you would find that in laminar winds, the threads stay pinned down the surface of the wing the entire time, whereas, in turbulent winds, you'd find the thread tufts fluttering quite a bit - especially towards the trailing edge. This would be a sure sign of inefficiency. Sounds like a great COVID Project, now that you've got your balance board done!! Keep up the great videos, thanks for all you share.
great discussion there, thank you. You raise an interesting point about time of the day as well. We personally find that wind is stronger in the morning (depending on direction) and lower in the afternoon as it warms up (except the thermals, south winds). In the evening the winds usually wind speeds pick up again on easterlies, and die down when they are southerly (thermals). With regards to attaching a small threads across the wing, that is actually doable, and we do have the time. Will see how it goes. So far we had barely any wind for past two months :(
Obstacles can cause turbulence, the IKO teaches instructors that a set of trees upwind of for example 10m high will cause unstable winds up to 7*Height of obstacle downwind. In this case 70m. It is called wind shadow Also the example that is given with the pipe does not completely compare with wind. since laminar flow in a pipe will automaticly become turbulent at a certain flow speed. The Reynolds number tells us if a flow is laminair or turbulent. For wind, which is not enclosed in a pipe this does not really imply as far as I can remember from fluid dynamics.
From our research, somebody used a laminar flow in a pipe as an analogy which made a lot of sense - we realize though that the flow in pipe vs wind are two different things, which is why we asked for some clarification from the community. With that said, in our experience, laminar flow kind of makes sense with regard to explaining steady wind vs turbulent wind - not gunna lie though, we're not sure how accurate it is, but a starting point for discussion
Great video thank you! I always thought that humid air would be heavier than dry air because water is heavy. I wonder if it's raining would that be more powerful because of the rain which is heavy moving at the same speed as the air.
Kinda late commenting on this one, but... My understanding was that the amount of energy per second delivered by the wind varies with the *cube* of its speed, not the square. A fixed block of air with a certain mass contains kinetic energy related to the square of its speed, just as you say. Double the speed, 4x the energy in that block. But if you double the wind speed, then twice as many of those blocks hit the sail every second, which doubles the energy again. 2x wind speed = 8x as much energy per second, 3x wind speed = 27x as much energy per second. That's why in sailing in general it's so easy to get overpowered as wind speed increases. Is there a factor with a kite that changes this?
Hey Blaik, from our research and from previous comments that we received, wind energy is square of its speed, curious where did you see that it is cube?
@@OurKiteLife High school physics: Kinetic energy of a moving body = 1/2 mv^2. So a block of air of a given mass contains kinetic energy proportional to the square of its speed. But as speed increases, more blocks hit you per second in proportion to speed again. E.g., double the wind speed, each block of air has 4x the energy AND twice as many blocks hit you per second. 2x as many blocks, each one with 4x the energy, so total energy delivered per second goes up 8x. For some independent confirmation, Google the phrase "wind energy as a function of speed". This mostly turns up articles on wind turbines and the power they generate. Here are a few that turned up from that search when I did it, all of which agree that power varies with the cube of wind speed: www.windpowerengineering.com/calculate-wind-power-output/ xn--drmstrre-64ad.dk/wp-content/wind/miller/windpower%20web/en/tour/wres/enrspeed.htm#:~:text=The%20wind%20speed%20is%20extremely,eight%20times%20as%20much%20energy. energyeducation.ca/encyclopedia/Wind_power openei.org/wiki/Wind_energy But a sail/kite is not a turbine, in part because it's in non-trivial motion relative to the wind when in use, and I don't know if that impacts things or not? Regardless, your essential point still holds - the amount of energy you're playing with can go up rapidly as wind speed increases. The prudent sailor/kiter should be wary... and excited. 😁
Great video guys! You made the science of aerodynamics entertaining. If you added in Bernoulli’s equation, you may pass as an aerospace engineer! Basically, the turbulent flow over the kite results from laminar flow separation on the upper side of the kite when you have gusty/shifty airflow passing the kite. In gusty winds, it is difficult for a rider to predict and react fast enough sheeting in and out to get the correct angle of attack to prevent the turbulent flow. Makes for an unpleasant day on the water. Good work guys! 👍👍😄
I don't think you understand Bernoulli's equation, it only applies to restricted flow(i.e. pipes) and applying it to an airfoil is wrong. This is the single most propagated aerodynamics misunderstanding on the internet. To be fair wikipedia has this wrong and there is published literature misusing the principle. If you want to read papers explaining how and why google for "Bernoulli's misuse". Also, turbulent wind is more than just gusty wind, as someone already mentioned there is a vertical component to turbulence. A simple gust is fairly easy to deal with, you sheet out or in and you are done. A turbulent gust hits you with rotors where wind changes direction much more rapidly and unpredictably than most can react making your kite overfly or stall into power zone.
Aviation - Aircraft has poor performance when in low density air.. example hot and high.. same theory in kites... Car as well.. poor performance hot and high...
Reasonable 'on earth' changes in temp, pressure and air density won't deliver a 3% difference in wind power. Giving relative measures of individual variuables is misleading and makes it sound like these have a huge effects. Turbulence and gradient have much more effect.
We did focus on extreme conditions, and we agree - if you're looking at kiting between 15 to 25*C the difference will be minimal. From our experience in snowkiting in -20*C and kiting in summer in 30*C, the difference is noticeable
Regarding turbulence, I'm not a meteorologist, but from a paragliding perspective; I'd agree the primary division is between 'ground obstacle induced', and prevailing air 'stability'. Whilst both are affected by the air-mass characteristics the ground obstacle impact is, of course, easier to predict. Turbulence within the air-mass itself is primarily caused, as you suggest, by the mixing of different air. Normally this is due to differing layers at height, and is crucial to distance paragliding as it is necessary to find warm 'thermals' rising thru' colder air in order to gain altitude. Naturally as warm area rises then colder air falls down to equate the pressures, and this the basic cause of turbulent gusts. On the ground you can notice the wind direction of these can be very different to the prevailing breeze. This much is pretty straightforward and explains, for example. why inland winds are almost universally more difficult to use than more laminar 'sea breezes'. (Coastal Cliff soaring a glider in such conditions can be almost 'hands off'). The more subtle point is that some days the 'edges' of thermals are relatively smooth transitions , whilst on other days they can be seriously turbulent (leading to various 'collapses' of the wing). Apart from differing windspeed gradients this is normally also explained by pressure and humidity impacts. Dry high pressure days can be expected to be more turbulent, which is explained as being due to the 'bullet' nature of thermals on such days.
We definitely have experience with thermal winds shutting off - it seems that they get quite turbulent right before it happens. Thanks for the explanation :)
What a couple of science nerds... Love it! ;-)
Thank Jeff :)
As always: clear, factual and well researched info. Thx Ourkitelife ! Now we need a device that blends all these effects together to tell you whether to go out and which kite to use.
honestly, I think one of the most addicting things about kiting is that you just never know how the session is going to turn out. So the solution you just go kite regardless
Love it how you take the science of kiting!
Thanks! If you have any ideas/topics you want us to cover, just let us know!
Great info. first time I’ve been glad to live in a cold, wet UK!
There are some perks to living in colder places - when the wind is good, it's really good :D
Great video. Love the technical details. Stay safe
Thanks, you too!
I love these type of videos. Thank you!!
Great info as always.
You can add 1 more and that would be water conditions.
I find flat water is easy on the kite, where as riding ocean with a lot of current swells and breaks takes almost 2 kite sizes bigger just to ride.
Yeah, goes hand in hand with weight :)
Great info. I often wondered why wind of the same speed does not have the same power you feel on the kite .
Surprised to learn an increase in humidity decreases the power of the wind. Thanks for the another great vlog!
Makes sense though, right? Denser air has more power. Humid air is less dense, tends to float up. Clouds float high in the sky on top of denser less humid air below.
@@jeffholt5783 Yes, dense air has more power makes sense. Intuitively I thought humid air was more dense than dry air.
Turbulence includes a vertical component. Close to the ground the might happen do to high winds speed shear just above the kitsters. Say if there are 80 knot winds at 800’ to 1000’ and 15 knots at the surface, that would creat plenty of eddies that would roll over each other and certainly include vertical velocities anywhere in the column.
Gusty describes just describes variable winds speed over short time periods. It might include a vertical component but this not measured in reported wind speeds.
thats some good info on turbulence vs gusts. Thank you
My mom was a meteorologist and I’ve spent 4 decades studying the weather so as to bore holes in it traveling around this ball.
Great video, and something I've thought about a lot - especially the laminar vs turbulent flow and just how significant of an effect it can have on kite power. I ride almost exclusively on foil kites, and spend a lot of time on Lake McConaughy, Nebraska in the summer. At that lake, there is a very predictable morning wind that feels quite strong, but once you get out, it has hardly any power. In the afternoon the winds speeds can be significantly lower and yet surprisingly provide much more power. I've come to call the morning wind "holey", and the afternoon wind "plump", or "buoyant". I've come to basically the exact same conclusion you have: in the morning there is a lot of thermal mixing going on, making the flow more turbulent, whereas in the afternoon the thermals have steadied out making the winds more laminar.
Aerodynamically speaking, I believe the reason this has such a significant impact on kite power is the following: in the gustier, more turbulent flow, I don't believe the air has the ability to fully attach and flow the full chord of the wing before it gets disrupted. This I'm guessing is causing premature flow separation on the topside of the wing near the trailing edge, kind of similar to what happens when a wing starts to stall. This means your wing is flying very inefficiently with a modified airfoil/airflow shape that looks nothing like it was designed to be; i.e low lift/high drag or low L/D ratio. In a nice laminar wind, however, the wind/air will stay attached the entire chord-length, just like the designer intended - and your kite performs like a dream - as it was intended. Too bad those laminar days are so few and far between for us inland kiters :)
What would be really fun is to take a kite and tape a bunch of small pieces of thread across the entire wing (or at least a wing chord section) like you might have seen in wind tunnel tests, and then somehow get a video of the top surface in the different types of air. I bet you would find that in laminar winds, the threads stay pinned down the surface of the wing the entire time, whereas, in turbulent winds, you'd find the thread tufts fluttering quite a bit - especially towards the trailing edge. This would be a sure sign of inefficiency. Sounds like a great COVID Project, now that you've got your balance board done!!
Keep up the great videos, thanks for all you share.
great discussion there, thank you. You raise an interesting point about time of the day as well. We personally find that wind is stronger in the morning (depending on direction) and lower in the afternoon as it warms up (except the thermals, south winds). In the evening the winds usually wind speeds pick up again on easterlies, and die down when they are southerly (thermals).
With regards to attaching a small threads across the wing, that is actually doable, and we do have the time. Will see how it goes. So far we had barely any wind for past two months :(
Great video guys ... love the way you filmed it as well as the content.
Thanks!
Love this channel
Thank you :)
“The power of the kite is somewhat dependent on how many beers you had last night”.
Now that’s something I wish I knew a long time ago 😁
Smoothie of Spirulina The night before is way better 😁
Another fantastic video! What software and method do you use to superimpose your holy image!?
Thanks. Software - magix vegas 17 and green screen with a 5 point light system
Great stuff, so much information so well summarized. Do you guys do anything with line length?
We always use 6m line extensions (even on our 7m kites) because we have gradient wind and all the wind is up high :)
Great video!!! such a silly question, i want to do an air meter, like these one in 0:51 in the video, have you guys some pictures of taht? thanks! 😀
Its from the spit in Squamish, British Columbia, Canada
Good stuff, I love the basic science side.
Thanks, glad to hear! If you have any ideas or topics for future videos, let us know :)
Obstacles can cause turbulence, the IKO teaches instructors that a set of trees upwind of for example 10m high will cause unstable winds up to 7*Height of obstacle downwind. In this case 70m. It is called wind shadow
Also the example that is given with the pipe does not completely compare with wind. since laminar flow in a pipe will automaticly become turbulent at a certain flow speed. The Reynolds number tells us if a flow is laminair or turbulent. For wind, which is not enclosed in a pipe this does not really imply as far as I can remember from fluid dynamics.
From our research, somebody used a laminar flow in a pipe as an analogy which made a lot of sense - we realize though that the flow in pipe vs wind are two different things, which is why we asked for some clarification from the community. With that said, in our experience, laminar flow kind of makes sense with regard to explaining steady wind vs turbulent wind - not gunna lie though, we're not sure how accurate it is, but a starting point for discussion
Great video thank you! I always thought that humid air would be heavier than dry air because water is heavy. I wonder if it's raining would that be more powerful because of the rain which is heavy moving at the same speed as the air.
it is counter-intuitive but humid air is lighter. With regards to rain, it makes the kite heavier for sure, not sure about effect on air density
Excellent
Thanks :)
Confinement due to Covid-19 affects far more than other parameters as my gears stay in the garage🥴😜
Kinda late commenting on this one, but... My understanding was that the amount of energy per second delivered by the wind varies with the *cube* of its speed, not the square. A fixed block of air with a certain mass contains kinetic energy related to the square of its speed, just as you say. Double the speed, 4x the energy in that block. But if you double the wind speed, then twice as many of those blocks hit the sail every second, which doubles the energy again. 2x wind speed = 8x as much energy per second, 3x wind speed = 27x as much energy per second. That's why in sailing in general it's so easy to get overpowered as wind speed increases. Is there a factor with a kite that changes this?
Hey Blaik, from our research and from previous comments that we received, wind energy is square of its speed, curious where did you see that it is cube?
@@OurKiteLife High school physics: Kinetic energy of a moving body = 1/2 mv^2. So a block of air of a given mass contains kinetic energy proportional to the square of its speed. But as speed increases, more blocks hit you per second in proportion to speed again. E.g., double the wind speed, each block of air has 4x the energy AND twice as many blocks hit you per second. 2x as many blocks, each one with 4x the energy, so total energy delivered per second goes up 8x.
For some independent confirmation, Google the phrase "wind energy as a function of speed". This mostly turns up articles on wind turbines and the power they generate. Here are a few that turned up from that search when I did it, all of which agree that power varies with the cube of wind speed:
www.windpowerengineering.com/calculate-wind-power-output/
xn--drmstrre-64ad.dk/wp-content/wind/miller/windpower%20web/en/tour/wres/enrspeed.htm#:~:text=The%20wind%20speed%20is%20extremely,eight%20times%20as%20much%20energy.
energyeducation.ca/encyclopedia/Wind_power
openei.org/wiki/Wind_energy
But a sail/kite is not a turbine, in part because it's in non-trivial motion relative to the wind when in use, and I don't know if that impacts things or not?
Regardless, your essential point still holds - the amount of energy you're playing with can go up rapidly as wind speed increases. The prudent sailor/kiter should be wary... and excited. 😁
I prefer Cabarete beach, to be in that freezing water 🙏
Warm water is really nice! Even in June we are in 5/6mm wetsuits 🥶
Use the stability index
What's that?
Hello Laurie and Yuri, I know a lot about turbulent airflow and gusts and can explain it to you, are you still interested?
Hey! Yes, we're interested. If it's easier, send us an email - you can find it on the 'Contact' page, or ourkitelife.com :)
Great video! Next time please leave out the music while you're talking. Its a little bit disturbing. And of course we just like to focus on you ;)
Noted, thanks! :)
Didn't feel any issues with the music...
Great video guys! You made the science of aerodynamics entertaining. If you added in Bernoulli’s equation, you may pass as an aerospace engineer! Basically, the turbulent flow over the kite results from laminar flow separation on the upper side of the kite when you have gusty/shifty airflow passing the kite. In gusty winds, it is difficult for a rider to predict and react fast enough sheeting in and out to get the correct angle of attack to prevent the turbulent flow. Makes for an unpleasant day on the water. Good work guys! 👍👍😄
Make sense as there's a very different feel from the kite in steady conditions vs gusty conditions
I don't think you understand Bernoulli's equation, it only applies to restricted flow(i.e. pipes) and applying it to an airfoil is wrong. This is the single most propagated aerodynamics misunderstanding on the internet. To be fair wikipedia has this wrong and there is published literature misusing the principle. If you want to read papers explaining how and why google for "Bernoulli's misuse".
Also, turbulent wind is more than just gusty wind, as someone already mentioned there is a vertical component to turbulence. A simple gust is fairly easy to deal with, you sheet out or in and you are done. A turbulent gust hits you with rotors where wind changes direction much more rapidly and unpredictably than most can react making your kite overfly or stall into power zone.
I’ve learned something today. If only we were allowed to kite.....
that would be nice to kite again :)
🤯
😄
Aviation - Aircraft has poor performance when in low density air.. example hot and high.. same theory in kites... Car as well.. poor performance hot and high...
Reasonable 'on earth' changes in temp, pressure and air density won't deliver a 3% difference in wind power. Giving relative measures of individual variuables is misleading and makes it sound like these have a huge effects. Turbulence and gradient have much more effect.
We did focus on extreme conditions, and we agree - if you're looking at kiting between 15 to 25*C the difference will be minimal. From our experience in snowkiting in -20*C and kiting in summer in 30*C, the difference is noticeable
@@OurKiteLife Yup and almost entirely due to wind gradient.