The Basics of Kite Power – How Does a Kite Create its Power?
Kite power is important – without it, we absolutely can not ride! Understanding why your kite flies and how it produces power is very helpful for beginner kiteboarders to know. Learning becomes ten times easier when you understand what you need to do to get the result that you want, and you really do get better faster. Now that makes a little theory worth it!
This page introduces a very basic version of the reasons why kites can fly and produce power. From this, we can show where one very important kiteboarding term comes from – the wind window! This page covers:
Note: The topics in this page can be extremely complicated. This kind of stuff is what rocket scientists at NASA study all the time – in fact, I spent a lot of time on the NASA website verifying the accuracy of this page before I posted it.
But, don’t be worried. I have taken this topic and written it in an easy to understand manner. For clarity, I have not included much of the small yet amazingly complicated details – unless you are designing your own kite, they don’t matter! The concepts in this page are all you need to understand the basics of how kite power is created.
How Kites Create Power
Kite power is produced in two ways:
The total kite power is a combination of these two phenomena, but each one has an area where it is stronger than the other. Let’s see where.
Lift is created as air flows over both surfaces of the kite. The air must flow over an area that has a shape like a wing. When this happens, the air flowing over the top of the wing flows faster than the air along the bottom – this creates a pressure difference. Because of this pressure difference the wing is pushed upwards, which is lift!
How Does Lift Depend on Speed?
The faster the air flows over the wing, the greater the pressure difference becomes, which results in more lift. So, if the air’s speed over the wing doubles, you would expect lift to double, right? Wrong! If the air’s speed doubles, lift becomes four times stronger!
E.g. If you are flying a kite at 10 knots and the wind doubles to 20, that exact same kite will pull four times harder than before. This is also why a kiteboarder who uses a small kite in 30 knots of wind can jump higher than one using a bigger kite in 15 knots - even though the bigger kite catches more wind. Say you have a 15 m2 kite in 15 knots of wind, and a 7.5 m2 (half the size) kite in 30 knots of wind – the 7.5 meter kite produces around twice as much power in 30 knots as the 15 meter does in 15 knots! That’s why it is better to learn to kiteboard on a larger kite in less wind, than a small one in high wind.
Where Does the Kite Have to be to Produce Lift?
For the kite to produce lift, it needs to have air flowing over its surface. Anytime this happens the kite creates lift – simple as that. The pictures below show where this can happen, and where it can’t.
Picture one and two both show kites with air flowing over their surface. Both of these kites are producing lift, but since the air flows further over the top of kite two, it creates more lift. Kite three is at too much of an angle to the wind. The air can’t flow over its surface, so instead is the air becomes turbulent – no lift in this case! To look at the same thing in a different way, the wind needs to “see” something like this;
but NOT this;
So, how does this last kite fly? The fact is, in some cases it doesn’t fly very well (we will get to that later) but in other cases it does…which leads us right into Wind Deflection!
Wind deflection is the second way kite power is created. The diagram below shows how this happens.
As the wind hits the kite’s surface two things happen. The kite slows the wind down and pushes it downwards, out the back of the kite. Thanks to Newton’s Laws, the kite gets pushed up and away. The kite flies forward, but does not move backwards because it is connected to your lines. Instead of moving backwards, it pulls on you, just like it did because of the lift!
Does Wind Deflection Depend on Speed?
It sure does. Wind deflection depends on the speed of the wind in the exact same way as lift (although the math is different, the relationship is the same). If wind speed doubles, the kite’s power quadruples.
Where Does the Kite Have to be to Deflect Wind?
For the kite to deflect wind, it needs to be in a position like the last picture. From the wind’s perspective, it needs to “see” this:
That’s it for wind deflection. Remember, total kite power is a combination of lift and wind deflection.
How Does Lift Compare to Wind Deflection?
Wind deflection is stronger than lift*. If you compare the strength of the two forces, a wind deflecting kite will pull harder than a kite that is just producing lift.
* When compared directly to each other. In this case, I am speaking of a stationary kite that is deflecting wind, and a stationary kite producing lift. A moving kite can create lift even if it is deflecting wind, which is not what we are talking about (yet).
What Does it All Mean?
Let’s tie this all together so it all makes sense. We know what the wind “sees” when a kite is producing lift and when it is deflecting the wind. We also know that a kite that is deflecting the wind pulls harder than one that is producing lift*. So, let’s see how this looks when you are flying your kite.
Is this starting to look familiar? If so, great! If not don’t worry… we have just stumbled across our next topic – the wind window.
To wrap this page up, the wind window is the area where we can fly our kite. It is broken down into two main parts: the edge, and the power zone. The edge of the wind window (also called the shoulder) is where a kite has the least amount of power. The power zone is where it has the most. Through the topics above, we can see exactly why this is!