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 Post subject: Re: Foiling with big kites
PostPosted: Tue Apr 29, 2014 7:25 pm 
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Joined: Sun Dec 15, 2002 1:00 am
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Location: Slovenia
Neusiedlersee. Nice spot. I was there once or twice 10 years back, when I was still on the windsurf. The water was very shallow on the spot if I remember corectly. How is it for foiling then?
The foils and the boards look nice!
Greetings,
Jaros


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 Post subject: Re: Foiling with big kites
PostPosted: Wed Apr 30, 2014 9:37 am 
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Joined: Sun May 23, 2004 4:32 pm
Posts: 99
it is not perfect for foilkiting but it is ok. sometimes you touch the ground. we also worked on a technique to start even when the water is less deep than the strut length. in some areas there is a muddy ground. it happended that my foil got stuck under water and i could hardly find it. there is also blackwater...

h.


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 Post subject: Re: Foiling with big kites
PostPosted: Wed Apr 30, 2014 5:42 pm 
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I'm following the foil development for a while and I'm close to getting into it.

@holden
could you comment on your statement
holden wrote:
i don't push the vmax any more because i had some bad crashes...

Can you give me some more infos on that? Is your foil getting less controllable at high speeds?

I was planning to buy a foil to get faster. :D

Currently I can get to 53 km/h on my airush sector V2 60 but that seems to be the limit for that board and I need 20+ knots. Its a ride on the edge of loosing control since I have to go on a down wind reach and then luff until the pressure gets to high to hold on. And at this winds we have ugly choppy waves from different directions that you have to take care of when going downwind fast.
I know, it is not the best board for top speed, but it is fun to go fast. Therefore I'm looking for something new.
.
I was hoping to get with a foil to this speeds in lower wind and to get the advantage not to have to care about the chop.

Related, but a little bit OT: I was looking at the Alpinfoils. Anyone with some experience with these foils? I read they seem to be pretty stable to ride.


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 Post subject: Re: Foiling with big kites
PostPosted: Wed Apr 30, 2014 5:55 pm 
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Location: Denmark
flying fish wrote:
I'm following the foil development for a while and I'm close to getting into it.

@holden
could you comment on your statement
holden wrote:
i don't push the vmax any more because i had some bad crashes...

Can you give me some more infos on that? Is your foil getting less controllable at high speeds?

I was planning to buy a foil to get faster. :D

Currently I can get to 53 km/h on my airush sector V2 60 but that seems to be the limit for that board and I need 20+ knots. Its a ride on the edge of loosing control since I have to go on a down wind reach and then luff until the pressure gets to high to hold on. And at this winds we have ugly choppy waves from different directions that you have to take care of when going downwind fast.
I know, it is not the best board for top speed, but it is fun to go fast. Therefore I'm looking for something new.
.
I was hoping to get with a foil to this speeds in lower wind and to get the advantage not to have to care about the chop.

Related, but a little bit OT: I was looking at the Alpinfoils. Anyone with some experience with these foils? I read they seem to be pretty stable to ride.


You are correct in expecting to be able to go fast in less wind, and not care about the chop :thumb:

BUT, having said that, even those very experienced (far more than me), have very rough chrashes when going full speed :o

You are a little meter higher up, so you hit the water quite heavy so to speak.

Especially because the contrast is immense - you can go 50km/h without much pull in the kite, and without using a muscle at all - just relaxing and flying at blistering speed with no sound at all :rollgrin:

But if your foil ventilates (which it often will, but less and less the more experienced), you will suddenlly go from a relaxed posture to a horrifying SPLAT and huge foil bomb, and some get their eardrums perforated !

So my experience is, that the contrast from hero to zero in a few tenths of a seconds, makes it quite exciting at times :naughty:

8) PF


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 Post subject: Re: Foiling with big kites
PostPosted: Wed Apr 30, 2014 8:05 pm 
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Location: PASA Level III Instructor FL- OBX - MI - the world
Peter_Frank wrote:

But if your foil ventilates (which it often will, but less and less the more experienced), you will suddenlly go from a relaxed posture to a horrifying SPLAT and huge foil bomb, and some get their eardrums perforated !
PF


Hi PF,
With all the discussion about hydrofoils lately we are seeing some terminology being thrown around in the threads. For us technical neophytes can you (or anyone else) explain a few terms for us?

difference between ventilation vs cavitation...and what causes them ? and how to prevent or reduce this from happening?

(a comment by Tone) Do you want to ride on apparent wind? or be slow and go on static wind.....what does this mean?

I would think that for the most part kites perform on apparent wind, since they are usually moving in one direction or the other - except when they are not moving completely stationary (which is somewhat theoretical)

cheers


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 Post subject: Re: Foiling with big kites
PostPosted: Wed Apr 30, 2014 8:14 pm 
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Cavitation is when a low pressure causes a fluid to change state from liquid to gas. Ventilation is when air is being sucked down from the surface.

Apparent wind is the wind speed the kite sees which is higher than static/true wind (I think the term true wind is better). If you move 1 m/s up towards the wind and the wind is 4 m/s the apparent wind would be 5 m/s. On top of this moving the kite around also generates more apparent wind for the kite.


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 Post subject: Re: Foiling with big kites
PostPosted: Wed Apr 30, 2014 8:25 pm 
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Location: PASA Level III Instructor FL- OBX - MI - the world
FrederikS wrote:
Cavitation is when a low pressure causes a fluid to change state from liquid to gas. Ventilation is when air is being sucked down from the surface.

Apparent wind is the wind speed the kite sees which is higher than static/true wind (I think the term true wind is better). If you move 1 m/s up towards the wind and the wind is 4 m/s the apparent wind would be 5 m/s. On top of this moving the kite around also generates more apparent wind for the kite.


OK...so now, in practical terms how does "cavitation vs ventilation" apply to foilboarding...with respect to design of the foil or techniques used to ride one?

Yes, I understand the concept of apparent wind no problem, and hopefully that is taught and is clear for anyone that learns to kitesurf or sail...

I would agree (and this is what I thought too) that "static" wind is the same as "true" ...I guess I was just wondering why someone would use a different term since "true wind" is the more conventional term in sailing sports. Maybe people use "static" wind in other disciplines, such as paragliding or other?

...and so what do you think the statement means?
"Do you want to ride on apparent wind? or be slow and go on static wind?"


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 Post subject: Re: Foiling with big kites
PostPosted: Thu May 01, 2014 9:13 am 
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robertovillate wrote:
FrederikS wrote:
Cavitation is when a low pressure causes a fluid to change state from liquid to gas. Ventilation is when air is being sucked down from the surface.

Apparent wind is the wind speed the kite sees which is higher than static/true wind (I think the term true wind is better). If you move 1 m/s up towards the wind and the wind is 4 m/s the apparent wind would be 5 m/s. On top of this moving the kite around also generates more apparent wind for the kite.


OK...so now, in practical terms how does "cavitation vs ventilation" apply to foilboarding...with respect to design of the foil or techniques used to ride one?

Yes, I understand the concept of apparent wind no problem, and hopefully that is taught and is clear for anyone that learns to kitesurf or sail...

I would agree (and this is what I thought too) that "static" wind is the same as "true" ...I guess I was just wondering why someone would use a different term since "true wind" is the more conventional term in sailing sports. Maybe people use "static" wind in other disciplines, such as paragliding or other?

...and so what do you think the statement means?
"Do you want to ride on apparent wind? or be slow and go on static wind?"


OK.

You can go out on a 7m kite in 25 knots and steam about the place, you may never really go faster than the wind and you're not really being that efficient. The use of the word static to describe wind was silly, I am not quite sure how to describe wind that will mostly be travelling faster than you will.

You can also go out on a 15m high aspect foil kite or race kite in as little as 8 knots and you might hit peaks of 30 knots if you're really tuned in to your kit and are very skilled. This is kiting on apparent wind.

For a definition of apparent wind http://en.wikipedia.org/wiki/Apparent_wind

with regards to cavitation/ventilation - I'd imagine any aero or hydro dynamic structures that can become less stable due to air passing across the surface of the wing. Windsurfers call is spin out and results in quite spectacular crashes. I wouldn't fancy spin out on a hyrofoil.


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 Post subject: Re: Foiling with big kites
PostPosted: Thu May 01, 2014 9:25 am 
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flying fish wrote:
@holden
could you comment on your statement
holden wrote:
i don't push the vmax any more because i had some bad crashes...

Can you give me some more infos on that? Is your foil getting less controllable at high speeds?

i will most likely get weak again and push the limit again...

on the foilboard you are constantly in an unstable equilibrium. any impulse you get to your system, you need to compensate. impulses can be: gusts, waves, seaweed, ventilation, under water turbulence when you cross the track of someone else and so on. if the impulse is bigger than you are able to handle, you crash. the faster you go, the shorter is the time you got for your reaction. sometimes you got no time at all. another problem is overreacting. for instance, the impulse lets the board come up, you react in putting more weight on your front foot but it is a wee bit too much, so the board goes down too fast, then you react on that but also too late and too much and the board goes up again and down and up until you crash... resonance disaster.

by the way, don't underestimate the underwater turbulence chop can create. you will be able to go faster in flat water. on the other hand you are able to reach your vmax in way less wind than with the sector so there will be less chop.

all foilboards have a certain vmax above which it is impossible to keep the board in balance even if the impulses are subtle. the vmax depends on the construction of the foil (length of fuselage, size of stabilizer, front foil profile and so on) but also on things like riders weight and obviously on the skill level of the rider.

due to the fact that you will crash when pushing the limit, i am always using a helmet with ear protection and i don't use straps. in the past crashes even in 40+km/h where mostly harmless. sometimes you bounce once on the water surface with you bottom and that's it.

three months ago i had two similar crashes that were not funny at all. i somehow go a rotation impulse when i left the board, i hit the water with my back and the head whip lashed back onto the water. since that time i sometimes felt a little pain in the neck when i moved the head in certain ways. it did not go away even after two months and i was about to make an appointment with an osteopath when i had this session with my twintip and the elf d8. i was practicing hand plant transitions. the first went ok but when i did the second, the kiteloop was to early or my rotation was not fast enough, eighter way, the kiteloop was yanking me out of the straps, me backwards, while flying i was thinking "nooooo, not again!", i hit the water with the back, whip lash... i got the board, started and while i went towards the beach, i was like "wait a minute, it is better now". since then my neck is back to normal again.

you can call me chiropractikiter.

h.


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 Post subject: Re: Foiling with big kites
PostPosted: Thu May 01, 2014 10:15 am 
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Joined: Tue Mar 11, 2014 10:02 am
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holden wrote:
three months ago i had two similar crashes that were not funny at all. i somehow go a rotation impulse when i left the board, i hit the water with my back and the head whip lashed back onto the water. h.


I had a similar experience one year ago.
Since then - when speeding - I wear a foam (very light) helmet that increase the drag of my head in the water when whiplash.
It worked nice two next times, but the speed wasn't much more higher.

Johnny Heinekenn in his famous video show an adapttation of an embryo posture in crash situations
and that may be even better solution, as it will work at higher speeds as well.

But it has to be automatic. How to get into it?


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