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Foil Kites - 4 knots ?

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kitexpert
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Re: Foil Kites - 4 knots ?

Postby kitexpert » Fri Aug 26, 2016 5:58 pm

Regis-de-giens wrote:So your 5+ is reasonnable for a standard tube kite, while a foil race kite could even reach 10+.
This race foil advantage certainly does not show when flying kites through the wind window, especially if kite is bigger. Foils are so heavy (have so much inertia) that with normal line lenghts there is not enough time/space to accelerate, and longer lines would increase the drag considerably. That is why how much lesser L/D ratio LEI's are better in active flying, they turn and accelerate faster.

Inertia explains (partly) how foils and LEI's produce their power. LEI gives more constant pull which is quicker available, race foil gives much more pull when given time to gain speed - before that its pull is quite weak.

Small race foils don't suffer very much inertia, because their volume is relatively small. If you double the area of foil kite its volume gets almost three times as big. This is true with LEI's too, but their volume is always quite small.

I don't know exactly how high race foils L/D is. Value 10+ sounds a bit too much, kites don't fly over 50kn speed through the wind window in 5knots. Nor is gliding from 2m height over 20m long, there is however drag of the kiter included in that example. Third method to measure L/D is to observe how high kite climbs, but this angle is difficult to measure exactly enough. Comparing different kites it is ok method.

I appreciate how you try to explain the basics - and you do it well, Regis. I see you understand the physics of flying, unlike certain overenthusiastic foilfanatic...

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Re: Foil Kites - 4 knots ?

Postby foilholio » Sat Aug 27, 2016 12:44 am

As usual twitspert you are fucking clueless. Racefoils have a huge advantage flying through the window, flying fast is actually what they do best, getting the most out of them requires good piloting. Which is unlike the fat pieces of shit you envision as being the greatest designs on earth. Leis(fat tube) are not better at active flying than fast foils, numerous riders have noted this. Your inertia rant sounds like PMU, exposing yourself? You need to gain a lot more experience riding(and flying), right now you are at kook level.

Regis-de-giens wrote: For a park-and-ride configuration, kite speed and rider speed is the same :wink: , hence my segregation between motor force (kite) and resisting force (kiter) in our low wind ride case. (*) OK; Now if you speak of a kite crossing the wind window, i.e. not quasi-static (i.e. kite moving not park and ride), the result will interest you .... it is quite the same ! if the kiter is static on the beach , the speed of the kite when crossing the window is ... vmax = L/D ratio * wind speed, which is by the way one method to measure the L/D ratio. So your 5+ is reasonnable for a standard tube kite, while a foil race kite could even reach 10+.

With long lines, top speed of the kite is almost the same, just need to add the drag of line extensions (and the fact that line extensions will tension a bit more the rear lines, so bar should be a bit more sheeted-out with the extensions to get the same AoA for both tests.

Now regarding the use of square or cubic speed in the equations it is quite simple : lift is proportionnal to (speed)^2 ; lift is a force ; if you want to know the power, power is always calculated as Force * speed , so leading to (speed)^3. Using forces (square of speed) in equations will help you resolving the pull and speed equilibrium you can have during a ride; power in itself does not bring a lot in discussions, except if you integrate along the whole waterstart phase, then you get the total energy (and back to square of wind speed). kite Energy could then be compared to the energy required to get out of water (i.e. lift 70 kg up to 1 meter high) and accelerate at a certain planning speed (say 5 knots) , so useful only for transient phases , like waterstart limits in low winds.

(*) I need to make a clarification for full accuracy: speed of the kite is the same as rider toward a fixed point ; but for the lift calculation you need to add the true wind speed before using the square function, as the wind speed the kite sees is higher than kite speed toward a fixed point.

I posted that link so some numbers for paragliders could be compared, yes 10+ is more accurate for race kites, I have seen 7 and 9 mentioned from some makers, maybe flysurfer and ozone. If we start comparing things like hang gliders or sailplanes which are also in that link and else where you'll see they achieve max L/D, Lift, Speed all at higher speeds than things like kites and at much higher levels. I think it is useful to use the kites limit or theoretical limit in calculations because I frequently use it to achieve maximum lowend, even riding were continual sineing are required to ride upwind, frequently I need to sine just to get on plane.

kitexpert
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Re: Foil Kites - 4 knots ?

Postby kitexpert » Sat Aug 27, 2016 11:53 am

foilholio wrote:You need to gain a lot more experience riding(and flying)
Really? I think almost fifteen years of kiting with longest day trips of 150km would be enough to say I do have some experience? I had kited perhaps 20 000kms before you foilholio even knew this sport 8)

I was two days ago with sonic15. It's flying speed through the window is not at all exceptionally good, but for a foil kite of that size it is though. Small race foilkites fly very fast through the window, but so does small LEI's.

It is a physical fact that big foil kites suffer from big inertia, because their total weight is so big. For example: Speed5 21: 3,94kg + 5kg air = 9kg in total.

foilholio
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Re: Foil Kites - 4 knots ?

Postby foilholio » Sat Aug 27, 2016 12:20 pm

I said you needed more experience ,in fact a lot more, never said you had none though now you raise it I wouldn't be surprised.

5kg wow massive huge fucking ginormous ! imagine if the airfoil was half as thick it could be only 2.5kg about the same as an inflatable bladder set.

Learn to ride.

PullStrings
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Re: Foil Kites - 4 knots ?

Postby PullStrings » Sat Aug 27, 2016 1:40 pm

foolkookio wrote:As usual twitspert you are fucking clueless.
Relax kiddo :allbegood: . I know for a fact that the expert has a lot more experience than you.
Hey what if i have also more than you ?

foilholio
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Re: Foil Kites - 4 knots ?

Postby foilholio » Sat Aug 27, 2016 11:19 pm

Considering you both lack part of the equation to complete the equation you are both idiots.


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