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 Post subject: Re: Back to the drawing board- how will we beat Sail Rocket?
PostPosted: Fri Nov 30, 2012 11:12 pm 
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Location: south east pa PKF SUX!!!
Why cant you compair a land kite to a water kite?

And sorry its the kite buggy land speed record

Even the best sail boat gets 2X on the water???????

Sailrocket is over 2X i think their in the 3X range and its a boat.

We are talking efficency of the system as a whole, if the board/ buggy/ boat whatever has alot of drag then that drags the system down. How fast would greenbird go with flat tires???

From the Greenbird site "A solution is required, where lift is maximised, BUT MORE IMPORTANTLY, drag is minimised.

The most drag at this point is the board to water interface. Maximise that and see where it goes.

OR throw lots of money at it and develop some kinda kite wing for super efficiency to make up for the drag of the board.


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 Post subject: Re: Back to the drawing board- how will we beat Sail Rocket?
PostPosted: Sat Dec 01, 2012 8:59 pm 
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Location: Vancouver
Unlike conventional sailboats and windsurfers, Sailrocket and kiteboards both utilize the same fundamental principle: net aerodynamic forces acting relatively in line with net lateral resistance forces.

Both variations of speed-seeking craft will progress to higher speeds.

Future Sailrocket-like adaptations will focus on stronger, larger structures to handle stronger wind and corresponding sea conditions, and also advanced 'breakaway' safety pods (PLEASE). It's conceptually simple to go a lot faster, and expensive (albeit more 'sponsorable' after Sailrocket's resounding success).

Speed kiteboarding is still in its technological infancy. Higher speeds will be achieved with rigid wing-kites with L/D ratios potentially 6-8 times those of current kites, more efficient (possibly 'stepped' and/or finned) boards, and various aerodynamic elements including suits and tiny-section line shrouds.

Cheers,
James


Last edited by JS on Sat Dec 01, 2012 9:37 pm, edited 2 times in total.

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 Post subject: Re: Back to the drawing board- how will we beat Sail Rocket?
PostPosted: Sat Dec 01, 2012 9:29 pm 
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BOARDS
At high speeds, 'wave making' resistance (related to spray) becomes less proportionally significant, and surface friction becomes more. Further, a board is essentially a 'ventilating foil', and although an outline that's more long than wide is more controllable, a short and wide outline is more dynamically efficient, like any other high aspect ratio foil. I suggest a 'stepped' board design such that, at speed, only two relatively short and wide 'strips' of board actually contact water.

FINS
The transition from 'attached' flow to cavitation would be a control problem for almost any craft at high speed. And though fins can be designed to operate at almost any theoretical speed without cavitating, sizes required to avoid cavitation-inducing pressure differentials results in prohibitive drag. Also, ventilation (at atmospheric pressure) is a practical limitation for almost any craft ripping across (an invariably rippled) surface at wild speeds, well before cavitation (at ambient water-boiling pressure) becomes an issue. The solution is to design fins for a state of permanent ventilation at high speeds. It appears to me surface-piercing racing props follow the same principle.

AERO ENHANCEMENTS
Speed kiteboarding suits would make a significant difference. Just picture a silly looking asymetric version of a speed ski suit. Kite lines could benefit from tiny teardrop-section shrouds to minimize losses to turbulence too.

KITES
The evolution of kites is about where high performance sails were not long after mid last century. For a clue to where speed kites can go, just look at where very high performance sails have advanced since then; examples include America's Cup yachts and Sailrocket. For kiteboarding, adaptation from proven foils like hang gliders and sailplanes makes evolution conceptually simple.

Cheers,
James


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 Post subject: Re: Back to the drawing board- how will we beat Sail Rocket?
PostPosted: Sun Dec 02, 2012 4:05 pm 
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I beat sail rocket every time I go kiting while driving to the beach. Then I ride waves, get huge air, try new tricks, have some beers with my friends. Let's put it in perspective. The sailrocket team has done nothing but work on sail rocket for several years while all of us including Rob Douglas have been busy having fun. At least we can go in more than one direction.


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 Post subject: Re: Back to the drawing board- how will we beat Sail Rocket?
PostPosted: Sun Dec 02, 2012 6:12 pm 
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http://www.peterlynnhimself.com/newslet ... Nl_12.html

Sounds like a pretty good analysis and potential solution.

Ciao

Mike


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 Post subject: Re: Back to the drawing board- how will we beat Sail Rocket?
PostPosted: Mon Dec 03, 2012 1:50 am 
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It's getting to the stage where you have to define what 'sailing' is and whether kiting really meets that criteria or should be a class of it's own. Maybe an overall wind powered record might be more applicable.


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 Post subject: Re: Back to the drawing board- how will we beat Sail Rocket?
PostPosted: Mon Dec 03, 2012 3:43 am 
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Look how there are different categories. This is how the various speed sailing records should be.

http://popeyethewelder.com/archives/12552


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 Post subject: Re: Back to the drawing board- how will we beat Sail Rocket?
PostPosted: Mon Dec 03, 2012 4:23 am 
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Mikey wrote:
http://www.peterlynnhimself.com/newslet ... Nl_12.html

Sounds like a pretty good analysis and potential solution.

Ciao

Mike


This article says "At around 45 knots or so, conventional fins 'ventilate'- that is, the water flow on their low pressure side can no longer be persuaded to follow an airfoil shaped curve. That this happens is pretty much an immutable law of the universe."

This doesn't make sense to me, for something to happen at a certain speed in knots? Maybe at a certain non-dimensional speed (Reynolds Number?)

Ventilation is usually air being sucked in from the surface, not water not following an airfoil shape? There's so many variables in foil shape, angle, and size. how can something just happen at 45 knots no matter what?


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 Post subject: Re: Back to the drawing board- how will we beat Sail Rocket?
PostPosted: Mon Dec 03, 2012 6:41 am 
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davesails7 wrote:
Mikey wrote:
http://www.peterlynnhimself.com/newslet ... Nl_12.html

Sounds like a pretty good analysis and potential solution.

Ciao

Mike


This article says "At around 45 knots or so, conventional fins 'ventilate'- that is, the water flow on their low pressure side can no longer be persuaded to follow an airfoil shaped curve. That this happens is pretty much an immutable law of the universe."

This doesn't make sense to me, for something to happen at a certain speed in knots? Maybe at a certain non-dimensional speed (Reynolds Number?)

Ventilation is usually air being sucked in from the surface, not water not following an airfoil shape? There's so many variables in foil shape, angle, and size. how can something just happen at 45 knots no matter what?


yes it sounds like 45 knots is the magical average speed turbulent flow must exist thus dramtically increasing pressure drop and drag....?????????? i don't know. i work reynolds numbers with pressure drops in small bore piping not foils....


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 Post subject: Re: Back to the drawing board- how will we beat Sail Rocket?
PostPosted: Mon Dec 03, 2012 2:22 pm 
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http://www.peterlynnhimself.com/newslet ... Nl_12.html

I think its a bit premature to be writing off windsurfers.

Sure there will be a cavitation problem if the pressure on the windward side of the fin drops too low. So you avoid the cavitation problem by changing the fin or board. There have been finless windsurf boards many years ago which had tucked down sharp rails.

Last week at Luderitz, they were suggesting that the wind was only about 35 knots when they recorded a 51.69 knots 500m. I'm a bit dubious that they could make that much of a difference by getting their gear tuned just right, because they set the top speed of 52.05 knots in winds of supposedly 40 to 45 knots only days before.

However, they do have a more efficient power source than the current kites, and a better speed to wind ratio, so they still have options.

Sailrocket though, gives them the same problem - they are going to need a revolution to compete with it, but at some stage craft like Sailrocket will get totally out of reach of something where a human is the ballast.


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