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Vegas 06 Test Reports (Del 2)

Skrevet av Gordon Hauge
16.12.05 20:59

Intervju med Andi Hanrieder - ekspert på aerodynamikk.

BOW HYPE:

KITEMAG: The development of bow kites completely redefined depower abilities. What used to be like letting off a bit of steam has evolved into a finely tuned system with a full throttle and a zero throttle position.

HANRIEDER: When conventional four liner tube kites are powered up or depowered, the angle of attack changes mainly in the tips while very little happens at the center. The fifth line helps reduce the angle at the center as well. Remember that in most tube designs the fifth line is only taut when the kite is depowered. The bow design allows one to reduce the angle of attack over the entire length of the kite through the bridle system. The angle can be reduced until the kite flutters but this depowering is not a gradual process. Not every point between zero and 100 percent power can be achieved. If you depower the kite, the power is reduced until a certain point when the profile collapses and the kite begins to flutter. This is the point where the lift coefficient drops suddenly. We call this the on-off effect.

Therefore, it is a common misbelieve that you can use a 16 bow kite in any kind of wind conditions. While it is true that you can effectively depower such a kite in a gust, which is a great safety benefit, it is definitely no fun maneuvering a size 16 kite at 30 knots.

KITEMAG: Is there a 100 percent depower?

HANRIEDER: It would still be a bit exaggerated to speak of 100 percent depower. A size 16 kite still retains considerable pull at 30 knot seven when fully depowered, its depower ability does not completely replace a safety function. This is why some bow kites are equipped with a continuous frontline to completely “flag” the kite. Most manufacturers do not supply an extra safety leash […]. The unpleasant pull of an inverted Crossbow is another problem we don’t even want to discuss here.

This sudden drop in lift (on-off effect) does not occur with ram air kites since the profile cannot begin to flutter and the kite will gradually depower. Therefore, airfoils offer a certain advantage over four liner tube kites, as their angle of attack always changes over the entire wingspan and the profile is able to change as well.

KITEMAG: Compared to C-kites, bow kites have the advantage of a huge wind range. Which construction features permit this kind of range? What is the role of the very stretched shape of bow kites that seems almost similar to ram air kites?

HANRIEDER: The increased low end performance is simply a result of a higher rate of projected area [less “wasted” surface in the tips that does not provide any lift]. Bow kite designs can vary greatly. A bow kite designed for maximum efficiency may have a slightly higher lift to drag ratio [higher flying speed, less diagonal force, better upwind abilities] than a conventional tube kite. However, when you build a kite you have to find a balance between the various properties and whether or not it is possible to achieve a higher maximum lift to drag ratio in the final product without interfering with other properties is doubtful. With regards to flying properties I would say that the bow kites that have been developed so far do not achieve higher lift to drag ratios than high performance tube kites.

KITEMAG: Bow kites are know for their very fast turning speed, are they also suitable for new school riders in your opinion?

HANRIEDER: The inside tip is able to work at very high angles of attack due to the swept arrow shaped leading edge. This works similar to the arrow shaped wings of a fighter jet by creating a leading edge vortex. Additionally, the outside tip is able to slack away extremely far. Both effects facilitate tight turns. However, this does not mean that the currently available bow kites are ideal for new school maneuvers. Quite the opposite is true, freestylers complain endlessly about bow kites. During kiteloops they hardly provide any pressure. Freestylers need an explosive pull to loop through wakestyle tricks. Furthermore, bow kites do not work so well when used unhooked.

KITEMAG: You can’t have everything. The Crossbow’s holding forces are relatively high. Why is that?

HANRIEDER: Most bow kite manufacturers have problems with excessively long steering travel. The trick to solve this problem are pulley systems at the bar ends. These systems not only reduce travel by half, they inevitably double the steering and holding forces as well. Takoon supplies the Nova without a pulley system and achieves much lower bar forces. However, this is only possible at the expense of very long steering and depower travel, which means that you cannot operate the entire depower range within the length of one arm without using the adjuster.

KITEMAG: Now it’s the hour of hybrid kites. The frontlines are attached relatively high at the front tube to increase the leverage.

HANRIEDER: The high attachment points of the frontline are crucial. North’s Vegas shows that such depower abilities can also be achieved in classical constructions. These kites also have the advantage that they cannot invert.

In the future, we will probably see different concepts emerging for each range of application. The designs will be as varied as the sport itself. Even if the marketing guys are trying to convince us that the bow concept is the future, it has definitely not won the race yet.

KITEMAG: Do you also expect that next year no kite will be sold without at least 90% depower ability?

HANRIEDER: It is obvious that depower ability will play an important role in the future, last but not least as a safety factor. However, a product that has nothing else to offer but great depower will not survive on the marketplace.

Resumée of the Vegas06’s benefits:

• Very direct bar feel

• Better low end and reduced drag

• Much wider wind range

• Soaks up gust

• Soft and smooth power development

• Soft and consistent pull

• Great for wave riding due to immense depower

• Different settings for different use (wave or freestyle)

• Easy water relauch

• Great hangtime

• Stepless depowering (no on/off)

• No delay between bar- and kite motion

• Max depower in ALL winds

• No reverse relaunch

All this is due to the North Cam Battens, the Trim Tip and Ken Winner’s great design!