Hi all,

Time for another KiteBud Freebie! Understanding how the kite flies and how it generates power are difficult concepts to grasp for the average kiter. Imagine how difficult it is to explain this to students

While working on a Kite Control video I decided to share this short sample for free to hopefully help everyone get a better understanding of those concepts. I'm sure even more experienced kiters will learn something from it



Happy Kiting!

Christian

I've been known to have a pull over a good kite session

Nice work.

Well demonstrated!

It's a nice demonstration overall. The video would be better if it focussed on the lift and angle of attack and left out the explanation of how the air is accelerated, because it's wrong.

The equal transit times explanation for the acceleration of the air was disproved some years ago. The air travelling over the top surface is much faster and reaches the trailing edge long before the air travelling on the lower surface. There's several videos that demonstrate it.

Here's one

There are several theories as to what is really happening, and they all have some merit, but the cause of the acceleration is not clearly understood.

The first half of this video explains it quite well and is reasonably easy to understand.

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Gorgo said..
It's a nice demonstration overall. The video would be better if it focussed on the lift and angle of attack and left out the explanation of how the air is accelerated, because it's wrong.

The equal transit times explanation for the acceleration of the air was disproved some years ago. The air travelling over the top surface is much faster and reaches the trailing edge long before the air travelling on the lower surface. There's several videos that demonstrate it.

Here's one

There are several theories as to what is really happening, and they all have some merit, but the cause of the acceleration is not clearly understood.

The first half of this video explains it quite well and is reasonably easy to understand.

Incorrect. Air over the top of an aero foil (any surface with camber ie curvature over the top surface) accelerates to meet the air flowing from underneath the aero foil at the trailing edge. The entire reason why air velocity increases over the top surface is that it has more distance to travel due to the curvature as opposed to the straight air path at the bottom surface. This process creates a pressure differential which generates lift. This concept applies to any aerofoil whether it be an aircraft's wing or a kite.

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cloudsurfer said..

Gorgo said..
It's a nice demonstration overall. The video would be better if it focussed on the lift and angle of attack and left out the explanation of how the air is accelerated, because it's wrong.

The equal transit times explanation for the acceleration of the air was disproved some years ago. The air travelling over the top surface is much faster and reaches the trailing edge long before the air travelling on the lower surface. There's several videos that demonstrate it.

Here's one

There are several theories as to what is really happening, and they all have some merit, but the cause of the acceleration is not clearly understood.

The first half of this video explains it quite well and is reasonably easy to understand.

Incorrect. Air over the top of an aero foil (any surface with camber ie curvature over the top surface) accelerates to meet the air flowing from underneath the aero foil at the trailing edge. The entire reason why air velocity increases over the top surface is that it has more distance to travel due to the curvature as opposed to the straight air path at the bottom surface. This process creates a pressure differential which generates lift. This concept applies to any aerofoil whether it be an aircraft's wing or a kite.

Then please explain whats happening in this video. There is no force in the physical world that requires two molecules of air that are adjacent to each other in an air stream, to stay in position relative to each other.

Love your videos Chris. I still need to get your self-launch video after the self-land video has been a huge help. I can literally now self-land in almost any wind speed (unless fully overpowered).

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cloudsurfer said..


Incorrect. Air over the top of an aero foil (any surface with camber ie curvature over the top surface) accelerates to meet the air flowing from underneath the aero foil at the trailing edge. The entire reason why air velocity increases over the top surface is that it has more distance to travel due to the curvature as opposed to the straight air path at the bottom surface. This process creates a pressure differential which generates lift. This concept applies to any aerofoil whether it be an aircraft's wing or a kite.

I have heard this explanation many times but it's actually not quite the truth. For example it doesn't explain why aerobatic planes can fly inverted and still produce enough lift to remain at the same altitude. There are other forces at play here too and the keyword is angle of attack (coupled with air speed).

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cbulota said..
Hi all,
Time for another KiteBud Freebie!

Dude......how do you make any money?????

Ya gotta stop giving sh!t away!

Man you guys over complicate things. Good video o.p.
Every comment after that was just the usual seasbreeze dribble.

Actually it's the video that overcomplicates things. All it had to do is say that the air over the top is accelerated (which it is), and leave out the reason why (about 1:00-1:10) because it's wrong.

There are multiple explanations as to why the air is accelerated. None of them by themselves explain the lift generated. The simplest thing would be to ignore it. Interested people can search the internet and find all sorts of resources that go into more detail.

Why try and explain something complex and nuanced in 10 seconds, and get it wrong? It's not as if knowing the cause helps in the understanding of the result. The aviation industry has ignored the cause for decades but jets still fly (even though they shouldn't be able to according to Bernoulli's theorem).

Thanks gojoe

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Gorgo said..
Actually it's the video that overcomplicates things. All it had to do is say that the air over the top is accelerated (which it is), and leave out the reason why (about 1:00-1:10) because it's wrong.

Point Taken, thanks for your input Gorgo, your knowledge is appreciated.

Christian

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mowingthelawn said..
Man you guys over complicate things. Good video o.p.
Every comment after that was just the usual seasbreeze dribble.

I think Chris and his video's are awesome and was just very surprised to see him get some basic physics wrong, but not that surprised due to the internet and the quantity of incorrect info available on the subject.

Newtons third law of Motion has more to do with explaining lift, and it is omitted in many of the explanations. www.physicsclassroom.com/class/newtlaws/Lesson-4/Newton-s-Third-Law

Air, being an "object" is deflected by the shape of the wing, so an equal and opposite force is generated. There are other forces relating to why aeroplanes fly too, but thats the main one that applies to why kites fly. This is because of the very low wind/air flow speeds affecting a kite, compared to an aeroplane.

Here is the revised version. Thanks for the Inputs



Christian

I have a question on this which may not be so bright but anyway ill stick my neck out.


In sailing when we discuss lift and apparent wind we are discussing the ability to sail closer to the eye of the wind or further upwind. are we talking about the same thing here or the ability to boost, or on reflection maybe we are talking one in the same in terms of power to do both more effiecently!

Maybe just some more overthought dribble on a discussion forum. god forbid!

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Ozone Kites Aus said..

cloudsurfer said..

Gorgo said..
It's a nice demonstration overall. The video would be better if it focussed on the lift and angle of attack and left out the explanation of how the air is accelerated, because it's wrong.

The equal transit times explanation for the acceleration of the air was disproved some years ago. The air travelling over the top surface is much faster and reaches the trailing edge long before the air travelling on the lower surface. There's several videos that demonstrate it.

Here's one

There are several theories as to what is really happening, and they all have some merit, but the cause of the acceleration is not clearly understood.

The first half of this video explains it quite well and is reasonably easy to understand.

Incorrect. Air over the top of an aero foil (any surface with camber ie curvature over the top surface) accelerates to meet the air flowing from underneath the aero foil at the trailing edge. The entire reason why air velocity increases over the top surface is that it has more distance to travel due to the curvature as opposed to the straight air path at the bottom surface. This process creates a pressure differential which generates lift. This concept applies to any aerofoil whether it be an aircraft's wing or a kite.

Then please explain whats happening in this video. There is no force in the physical world that requires two molecules of air that are adjacent to each other in an air stream, to stay in position relative to each other.

There is no force in the physical world that requires two molecules of air that are adjacent to each other in an air stream, to stay in position relative to each other.

Maybe there is at the quantum level

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Ozone Kites Aus said..

Newtons third law of Motion has more to do with explaining lift, and it is omitted in many of the explanations. www.physicsclassroom.com/class/newtlaws/Lesson-4/Newton-s-Third-Law

Air, being an "object" is deflected by the shape of the wing, so an equal and opposite force is generated. There are other forces relating to why aeroplanes fly too, but thats the main one that applies to why kites fly. This is because of the very low wind/air flow speeds affecting a kite, compared to an aeroplane.

Deflection is important, but it only accounts for a minor part of the lift generated if you calculate the forces ( www.grc.nasa.gov/WWW/K-12/airplane/wrong2.html ). Also, if it were only up to deflection there wouldn't be a stall angle because more angle of attack would simply mean more deflection and more lift (www.grc.nasa.gov/WWW/K-12/airplane/incline.html )

The simplest explanation I've seen is that the wind is split at the leading edge into a section deflected down and a section above that tries to remain in the same position. However if the wind above remained in the same position there would be a massive, wedge-shaped vacuum formed behind the wing between the 2 split streams. The vacuum will pull the wind above it down, as well as attempt to pull the wing up to fill the vacuum. As the wind above bends to fill the vacuum, it also speeds up as it's being sucked into the vacuum (technically just a pressure differential). Now that there is a LOT of wind heading down (both below the wing and directly above the wing), it sucks even more wind downward from the next layer above the wing. All of this bending of the wind downward causes an opposite force lifting the wing upward.

So 3 main contributors of lift: the deflection, the pressure differential behind the wing, the pressure differential from the downwash.

The NASA site has good coverage of all the parts that affect lift, but gets pretty heavy into math: www.grc.nasa.gov/WWW/K-12/airplane/right2.html


... and great updated vid Christian. I love that short line kite as it clearly demonstrates angle of attack changes. Do you tackle apparent wind too?

Nice explanation VRBones !! Ive done a lot of wind sports and also flying - gliding and stuff with the fan on the front and never had such a simple and clear explanation :-)
Well done Christian for the Vid but perhaps one thing you missed that beginners often ask but cant get thier head around - if kite is moved slowly from one side of the wind window to the other not much power is generated - but if you rip it through the window it generates a massive amount of power - why? This in part is due to the angle of attack but I strongly suspect is more to do with the speed of the kite ? A plane wing with low airflow generates bugger all lift - but as the speed doubles the lift increase to the power of 4 as you pointed out - and at some point the air speed over the wing will generate enough lift to get the plane off the ground - this is always a gradual increase as it takes time to get a plane up to the critical speed - But not so with a light weight 'wing' like a kite - pull the bar and very quickly the kite will accelerate across the wind window and due to the speed generate massive amounts more power than a beginner ever imagined !!!!!
The video focuses on the angle of attack for lift and power but doesnt really touch on the flying speed of the kite - and this is the one that catches most begginers out !!

the important thing is this video features IKON kites :) Nice video. I have explained it simply as:
1) if you pull on the bar you increase the angle of attack and lift until you stall it. So your kite is too powered, let the bar out. If your kite is stalling, let the bar out.
2) if you fly (or loop) the kite you generate lift because air moves over the foil faster. So sine or down loop to get going.
3) the faster you go, the more lift you get with higher apparent wind speed over the kite. So if you are over powered and going too fast, ride at your kite to take some power out of the sail then edge hard.

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Lambie said..
Nice explanation VRBones !! Ive done a lot of wind sports and also flying - gliding and stuff with the fan on the front and never had such a simple and clear explanation :-)
Well done Christian for the Vid but perhaps one thing you missed that beginners often ask but cant get thier head around - if kite is moved slowly from one side of the wind window to the other not much power is generated - but if you rip it through the window it generates a massive amount of power - why? This in part is due to the angle of attack but I strongly suspect is more to do with the speed of the kite ? A plane wing with low airflow generates bugger all lift - but as the speed doubles the lift increase to the power of 4 as you pointed out - and at some point the air speed over the wing will generate enough lift to get the plane off the ground - this is always a gradual increase as it takes time to get a plane up to the critical speed - But not so with a light weight 'wing' like a kite - pull the bar and very quickly the kite will accelerate across the wind window and due to the speed generate massive amounts more power than a beginner ever imagined !!!!!
The video focuses on the angle of attack for lift and power but doesnt really touch on the flying speed of the kite - and this is the one that catches most begginers out !!

Good Point.

Remember this is a Sample. The full (Paid) video will cover all these aspects, I can't give everything away for free

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VRBones said..

... and great updated vid Christian. I love that short line kite as it clearly demonstrates angle of attack changes. Do you tackle apparent wind too?

I will at some stage yes, however a lot of other videos to work on first.

I have been a commercial pilot for 36 years and this very simple explanation of lift is still taught in all the flying schools to this day.

In order to meet up at the trailing edge, the molecules going over the top of the wing must travel faster than the molecules moving under the wing. Because the upper flow is faster, then, from Bernoulli's equation, the pressure is lower. The difference in pressure across the airfoil produces the lift.