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 Post subject: Foils with handles for racing?
PostPosted: Sun Jul 04, 2010 1:06 pm 
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I just met a guy, who once had the speed record for buggy kiting...127 km/h. Faaaaast!

I told me, that due to handles you can trim the kite way more than others to make them fly into the wind further. Much further than a e.g. a waterkite foil from Flysurfer.

Did anyone try this out yet? Sure, you shouldn't drop it...but it is possible to race with it.

Anyone with a more knowledgeable mind who could could comment on it?

Thanks
Toby


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 Post subject: Re: Foils with handles for racing?
PostPosted: Sun Jul 04, 2010 1:31 pm 
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Hi Toby,

For sure it's possible, but it's not so easy and there are certain factors that differ from Racing with a Buggy on land and racing on the Water.

It's pretty well known that an Open Cell Fixed Bridle Kite will have much more performance potential than a closed cell depowerable kite. There are drawback however. Buggy race kites are notoriously unstable, and really need an expert flyer to get the maximum out of them. In gusty winds they really can be a handful. They always need to be "braked" back from a full frontal stall durning maneuvers.

Most Buggy kites can be trimmed for various conditions and needs, but there is always a compromise between stability and performance.

Lets say we have perfect laminar wind conditions. Then a guy using a fixed bridle kite will have a chance. They do stay up in very light winds, and you can use a smaller kite and shorter lines.

BUT.

Without powercontrol (eg Depower), the kite will have to be worked more to get going, which will be a deficit at the start.

Also, buggy race kites have less "pull", they drive towards the edge of the window and make you go fast, but they do not have the same torque as a depowerable kite and the downwind technique will be quite different. They are designed to not pull you sideways at high speeds.

There is also the factor of relaunch and getting the kite wet. Most buggy race kites are not coated to be water resistant, and if the get wet they will loose a lot of performance, and will get even more difficult to control.

I am not saying its impossible, but very difficult to race on the water with an open Cell fixed Bridled kite.


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 Post subject: Re: Foils with handles for racing?
PostPosted: Mon Jul 05, 2010 4:56 am 
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I had a MacPara 6m Neptune, a closed cell version of the Mac Bego which is a very efficient race kite type profile and beloved 4 line handle kite for light winds which many compared to the 10.5 Blade in power.

It is very challenging to kitesurf with this kind of kite. To have the power you need to really truck upwind on the water it is very scary when standing on the beach, like an old two liner.

Like Gunnar said, Depower is a big big deal we all take for granted.

I do wonder about using racekites with a depower mod like Manfred's UDS or the LOCO blade mod.

Maybe then foils will rule?


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 Post subject: Re: Foils with handles for racing?
PostPosted: Thu Jul 22, 2010 2:55 pm 
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in sailing, it is the combination of aero and hydro parts working together.
depending on the masses and drag, optimal performance comes from a combo of power and efficiency in both aero and hydro parts.

the weakest link in the efficiency pairing is by far the greatest determinant of overall performance.

1. for buggies, the resolved lateral l/d of the wheels is HIGHER than the resolved lateral l/d of the kite. therefore any gains in kite efficiency are worth sacrifices in ease of use. also, once at speed, buggies travel at greater windspeed multiples over a smooth terrain and variations in true windspeed are reduced in apparent magnitude. there is also no great "low speed drag hump" or energy budget that has to be overcome in order to accelerate from a standstill. so a small kite can be used that is sized to deliver optimum pull when at max speed.
i.e. sheeting doesn't matter much or even at all, ease-of-handling requirements are lower and therefore raw kite l/d is king.

2.for fins/kiteboards , the resolved lateral l/d of the fins+board is LOWER than that of the kite. therefore gains in kite efficiency deliver relatively marginal benefits beyond a certain point and it is more appropriate to focus on kite performance factors that allow improvements in the use of the board+fins. i.e. steady consistent loads delivered, and ease of handling allowing the rider to focus on the RIDING.
There is also the fact that in order to accelerate from a standstill(get planing), a large pull is initially required to get over this energy hurdle, but then the lift coefficient needs to be reduced at high speeds in order to prevent overpowering the fins+board+rider. In other words, we choose kitesize for what delivers at low-medium speeds, and then reduce power at higher speeds so as not to become too overpowered.
Furthermore , the kiteboarder operates at lower multiples of the true windspeed than a buggy, and has to be able to stand around on the beach with a more powerful kite than a buggier, and thus experiences greater effective gust amplitude. So "surge" is a greater problem and the profile needs to either be a little detuned compared to a buggykite, in order to deliver a smoother response over a wider range of pitch parameters.
i.e kitesurfing requires larger kites to deliver big initial pull but that can also be sheeted out in order to moderate the increasing loads produced at the higher speeds racing.they also must be able to deliver stable consistent loads,and require less piloting concentration. These extra performance factors require a tradeoff in raw l/d.

this isn't to say that you can't kitesurf with a large buggy-kite type of design...I used to own an 8.5m blade for the purpose. but high speed was pushing the limits of board control with such a powerful yet unsheetable kite. modern kitesurf kites are leagues better for racing on water.

@jake- hey dude , even with those speedmods or whatever, the buggy-kites are still probably too responsive to surge; remember what flying an original SPEED 7m in the top half of it's windrange was like? a bloody handful, even with the sheeting system it had...
in fact i don't think that the speed2 or speed3 have really delivered any gains in efficiency over the speed1, they are just much more refined in terms of gust response, handling, sheeting and the like. I guess that underlines my whole arguement really.

Beyond a point raw l/d in a waterkite becomes unimportant if it is only achieved at the expense of other factors. It is always nice to have a bit more of it though, if it can be delivered without compromising the gains made in other areas...


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 Post subject: Re: Foils with handles for racing?
PostPosted: Thu Jul 22, 2010 4:27 pm 
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Agree about the speeds - my speed 1 13 seems to have a similar low end to a sp3 15 - much worse top end though


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 Post subject: Re: Foils with handles for racing?
PostPosted: Sun Jul 25, 2010 11:00 pm 
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Rabidric wrote:
...
2.for fins/kiteboards , the resolved lateral l/d of the fins+board is LOWER than that of the kite. therefore gains in kite efficiency deliver relatively marginal benefits beyond a certain point and it is more appropriate to focus on kite performance factors that allow improvements in the use of the board+fins. i.e. steady consistent loads delivered, and ease of handling allowing the rider to focus on the RIDING.


Even with the latest race boards which are really impressive when going upwind ?
Any guess with the hydrofoil kitesurf boards which have a better upwind angle than the above-mentionned race boards ?


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 Post subject: Re: Foils with handles for racing?
PostPosted: Mon Jul 26, 2010 1:12 pm 
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The speed 7 was such an epic kite when conditions were right, but you are right about gusts. I remember trying to ride waves with that kite and sometimes a gust would not only pull me off a wave I was on, it would send me over the backs of 2 more before I could gain control.

But I think raceboards are pretty close to the point in efficiency where the kite is starting to matter. I have not been following results, but my understanding is that the foils are competitive upwind but are getting smoked on the downwind leg?

One of the most intelligent foils vs single skin kites I have read was from the Revolution design team regarding the powerblast 4->8. They state that a single skin kite operates at higher angle of attack without backstall, giving the kite more power. Possibly even more significant, is that after a stall, laminar flow is established over the wing more quickly, so there is more power on demand or sooner after a pilot error. My experience confirms this, and thus in adverse sailing conditions like waves, I get more power out of an LEI, whereas in flat water the foil is going earlier for me and jumping higher.


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 Post subject: Answer for Toby
PostPosted: Sat Dec 25, 2010 11:45 pm 
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As someone who often rides kite buggies, kitesurfs, and snowkites, I can tell you that a high aspect open cell foil would be unbeatable on the water. The problem is that using handles is sijmilar to riding unhooked, so it would require tremendous skill even to maintain balance on a board because the rider's upper body would be constantly pulled over the board. One of the most difficult activities in kite buggying involves getting into the kite buggy with a high aspect ratio kite 10 meters or over (fixed bridle) in winds over 15 knots. Once the rider gets into the buggy, some of the pull directly transfers to the buggy. This is not possible with a kiteboard because it does not have wheels and encounters more friction. Also, the fastest speeds on the kite buggy were recorded with a light, small fixed bridle kite because they move much faster than larger kites. There have been successful attempts kiteboarding with handles, however, but not for sustained periods of time. I use my Crossfire II 10 meter fixed bridle kite in 2-4 mph winds on a Flexifoil kite buggy with extra wide wheels (and the standard axle), and I would say that the Crossfire II 10 m fixed bridle kite is equivalent to a 20 meter inflatable kite. It requires constant input from the handles and a great deal of finesse to ride with a kite landboard, and when the wind is not smooth, it tends to require even more input. On the kite buggy, the kite flies much better because the buggy generates enough speed and momentum for the kite to remain powered up through lulls. A fixed bridle kite in the water will fill up with so much water that it will become a permanent sea anchor as well!


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 Post subject: Re: Answer for Toby
PostPosted: Sun Dec 26, 2010 2:26 pm 
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Raphael wrote:
The problem is that using handles is sijmilar to riding unhooked, so it would require tremendous skill even to maintain balance on a board because the rider's upper body would be constantly pulled over the board.


Since your are an experienced rider, I'm surprised that you make this kind of comparison without proposing THE buggyist solution as old as kite-buggying itself (25+ years :o :o ) that would allow to apply 90% of the kite pull at kiteracer hips level.

Last but not least, this low & single traction point acting as chicken loop would allow the kiteracer to ride his board flat hassle free with minimum effort as with any LEI :o :o

OK, kite sining would not be as easy as with a bar but this would be outweighted by the fine tuning possibilities and "back-loop" feeling provided by a pair of handles :D
Safetywise, as in any kite buggy system, both front lines could be attached by transverse link just above rider's head.
Emergency depower with this gear just means releasing the handles and catching the transverse link.
In case of kite release, the leader line transverse link can be attached to harness.

This is just a new learning curve and new habits to catch ...

Quote:
The Prodigy Spreader Bar is fully articulated in both the up and down as well as left-to-right axis and spins as well, so you can untwist the lines after a kiteloop, downturn, or upwind jibe. It also feature a plastic tab that helps keep the strop engaged in the pulley when spinning it around.


Attachment:
StropComp2.jpg
StropComp2.jpg [ 41.09 KIB | Viewed 1296 times ]

Image

I wonder how it would be riding a Cabrinha Crossbow with such linked handles + suitable spreader bar... : + innovative line length ajustment system .... :baby:

Many times, I have thought about keeping the spreader bar pulley but replacing each handle shown on above pict by a pulley and driving the kite with quarter turn individual handles embracing both rear and leader lines allowing to choose between :

Kite rotation or kite sining
- leader line handles: both turned outwards (natural position for kiter) allowing rear lines and front lines to be stuck together. Both handles travel in opposite direction.
- spreader bar pulley: in action
- front line pulley: fixed, no rotation.

Front / Rear line differential length or kite AoA adjustment
- leader line handles: turned inwards (temporary position) allowing action on front line only. Action can be performed on one handle only or on both simultaneously.
- spreader bar pulley: not used
- front line pulley: used and rotate according to handle that is in inward direction.

Picture credit (I am not affiliated): http://www.coastalwindsports.com/servlet/the-500/Harness-Rope-Strop-ProLink/Detail
http://www.coastalwindsports.com/servlet/the-677/Peter-Lynn-Divine-seat/Detail


Last edited by Europ2 on Sun Dec 26, 2010 5:42 pm, edited 2 times in total.

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 Post subject: Re: Foils with handles for racing?
PostPosted: Sun Dec 26, 2010 5:27 pm 
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Actually, riding hooked into a F.B. foil and sining the kite is very bloody easy - on the handles, you just tweak the brake (pull the bottom of the handle) and let the kite fly - because you're not messing with the AoA so much, the kite is flying as fast (and as efficiently) as it can almost constantly, depending how ham-fisted you are on the handles. Apparent wind HELLO! man battle stations, batten down the hatches and hang on for dear life :o

Safety systems can become problematic though ...


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