How a depower kite works

How a depower kite works:

A depower kite is, as the name suggests, one where the kite flier can control the power output of the kite.

A depower kite works by changing the angle of attack of the kite. Basically, a kite can be thought of as an airplane wing. When an airplane is flying normally, the wing is in a more or less flat position, providing lift to keep the plane in the air, but also reducing drag to allow the plane to fly faster. However, when a plane is taking off, it need more lift to get into the air, whilst speed isn't so important. The wing is tilted upwards as the plane takes off, giving the necessary lift. When the plane levels off, it goes into speed mode.

In a kiting context, this means that when the kite is tilted flat to the wind (as above) the lift and power is at a minimum, but because drag is decreased, the airspeed increases.

In the picture above, the kite is fully powered. In comparison with the other picture, you can see that the kite is tilted upwards. This increases lift and power, but also increases drag, making the kite slower through the air.

A depower foil works by bundling the brake bridle together with part of the power bridle to create, in effect, a second power bridle. The flying lines from the brake bridle go to the tips of a special bar, whilst the power lines go through a hole in the middle of the bar and are attached directly to a harness via a 'chicken loop' as shown below.

The bar is not in a fixed position, but has a limited range of movement up and down the lines. When the bars is pulled in toward the kite flier, as in the 'maximum power' picture above, the combined brake and power bridles are tensioned, changing the pitch of the kite upwards and increasing the power and upwards lift. Equally, when the bar is pushed away by the kiter, the 'brake' bridle is slackened off and the kite returns to its minimum power position.

By careful placement of the bar, you can control precisely how much power is put out by the kite. This can be very handy in gusty conditions, as the power can be adjusted to compensate for the wind strength.

You can see in this picture how the two bridles are combined, then joined together to limit the movement of the bar.

Different kites have more or less effective depower systems, with some kites able to go from almost no power to full power very easily. There are a few other ways of altering the power output of a depower kite, such as trimmer straps. In the case of some kites, an extra cleat is fitted onto the power lines just in front of the bar. By pulling on a rope attached to the power lines, it is possible to lock off the lines at a given position and use the bar for fine tuning the amount of power you want.

The Peter Lynn venom has a further contribution to depower – it has a trimming strap inside the kite itself, meaning that the range of depower available in this case is extremely large.

A depowerable kite has less power (even when fully powered up) than the same sized fixed bridle kite. So a 9m depowerable will have, as a rule of thumb, the power of roughly a 6m fixed bridle kite, though there are a number of other factors that affect the power output. The advantage is that a depowerable kite can be safely flown in winds where an equivalent fixed bridle kite would be completely overpowered and unmanageable. They can be used in a much wider range of wind conditions.

On land, depower kites are mostly used for kiteboarding and buggy jumping, as they work best with air flowing over them (called apparent wind, created by the constant movement of the kite when boarding etc). They can be used for static flying, but normally fixed bridle kites have the advantage there.

Depowerable kites are also used for kitesurfing on water, though the kites used in this case are almost invariably 'closed cell' or 'leading edge inflatable' kites, meaning that they are inflated then sealed off, so they can be landed in water without any getting inside the kite and making it impossible to fly. It is important to use depowerable kites on water because kitesurfing needs much more power than land based activities – a depowerable kite can be launched on minimum power, then the power increased to the necessary level once you're out on the water.

Disadvantages of depower kites:

They are more difficult to fly than fixed bridle kites because of the extra dimension of complexity involved. Also for the most part, they don't fly well (or at all) in below about 8mph, with some kites needing almost double this windspeed. This trend continues as the size of the kite increases – even the biggest depower can't be flown in low winds with much ease. Fixed bridle kites, however, have far better low wind capabilities.

Types of depower kite:

There are various types of depowerable kite, such as C-shape LEI's, depowerable foils (covered in detail above) and bow kites. LEI stands for Leading Edge Inflatable, as these are single skin kites with an inflatable bladder in the leading edge which controls the shape of the kite, thus dispensing with the need for bridle lines. These are also depowered by changing the angles of attack, as are bow kites, but the methods are different in both cases. Bow kites are a cross between LEI's and foil kites – they feature the best aspects of both including an excellent depower system and massive wind range.

Depower and fixed bridle kites: a comparison.

Depower kites

- Much greater wind range

- More complex to fly

- Good for boarding and buggy jumping. Not so good (generally) for static flying.

- Able to jump much higher

- Generally much more expensive

- Can be made much bigger

Fixed bridle kites

- Not such a good wind range – you need to change kite size often as the windspeed increases.

- Much simpler to fly

- Good for static flying as well as boarding and buggy racing

- Not able to jump as high (safely)

- Generally better value for money

- Power can be difficult to control beyond 9/10m, though some racekites go larger; e.g. u-turn nitro (15.4m)

Depower kites on handles:

Whilst it is possible to fly a depower kite on handles and have it power up by pulling the brake lines, you lose the effect of the depower system and you're left with a low power, heavy fixed bridle kite with bad low wind capabilities and (obviously) no depower.

I hope this has helped to clear up any questions you might have. I'm going to add just one more section:

Developments in depower:

No-one is exactly sure who made the first depower kite, though whoever it was, depower kites have come on leaps and bounds since then.

The latest generation of bow kites has been launched this year. A cross between foils and LEI's, these kites are easier to fly than ever and they have a total depower system – you can power down from full, 40ft jumping power to no power at all, and stand there as the kite comes down in 30mph. Modifications are being made all the time to existing depower kites, with many manufacturers now attempting to reduce the complexity of the bridle system by supporting the kite internally whilst retaining the performance characteristics of a bridled kite.

Flexifoil have brought out their improved sabre, and flysurfer have launched two kites now that can be totally depowered like a bow kite whilst retaining the performance of a foil kite. I'm looking forward to seeing what comes out next, and then flying it!

Author : MatJ