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hydrofoil at max speed limit

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Peter_Frank
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Re: hydrofoil at max speed limit

Postby Peter_Frank » Sat Dec 02, 2017 9:51 pm

Against stupidity even the gods themselves struggle in vain :roll:

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Re: hydrofoil at max speed limit

Postby gbrungra » Sat Dec 02, 2017 10:01 pm

Max speed of a kite could be found if only we could find a frictionless, drag-less rider... maybe a guy on ice skates in a speed suit? Or no rider, but an autopilot steering the kite, tethered to a maglev rail? Probably not a true max speed, but a varying max across a range of wind speeds?

But back to the foils, it seems we can agree a true speed foil would be small in area, flat in profile (low lift, low drag), and stabilizer would have low angle of attack (maybe zero angle of attack, with negative lifting profile, like zeeko foils). Such a foil would have a very high lift-off speed, so part of the challenge is finding very flat water to be able to ride fast enough of the surface to start foiling. But I'm sure the speed challenge guys will be trying it within a few years.

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Re: hydrofoil at max speed limit

Postby revhed » Sat Dec 02, 2017 10:16 pm

Peter_Frank wrote:
Sat Dec 02, 2017 6:59 pm
even draggy low performing kites can go unlimited fast, when it blows sufficiently and you ride on a downwind course.
We have actually seen this quite often when talking speed records - crazy high winds and a normal low aspect kite, has been used for many of these - riding a deep downwind course.
8) PF
https://video.search.yahoo.com/yhs/sear ... ction=view
This sure does NOT look like and is NOT a deep downwind course!
So you are wrong AGAIN!
No such thing as "unlimited fast"!
As for the gods, they must be crazy!
R H

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Re: hydrofoil at max speed limit

Postby kiterocky » Sat Dec 02, 2017 10:23 pm

Waiting rider with 50kts wind and hydrofoil....hahha
:bye: :bye:

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Re: hydrofoil at max speed limit

Postby Horst Sergio » Sun Dec 03, 2017 1:46 am

Don't think it is all about stupidity, relativistic speeds, nor experiences of breaking foils due to high load during fast speeds.... or anybody here with those experiences ... going more than 30000 km/s , anybody? ... No? :roll: So better stop :argue: and back to :allbegood: :remybussi:

Apart from what Peter Frank said IMHO control of forces and speed is the most important factor. And this depends from skill, rider weight, wave hight, wind speed, foil and kite size and design.

Additionally vibration disasters may cause the experience that there are kind of personal max speeds per foil. Those speeds just can be increased a bit by physical training and better skill or body position, as for example using those strange seat harness and taco position....

just the low experience of somebody never exceed 50 km/h ... maybe one day I will buy myself into 30 knts world with a smaller wing, till then enjoying slow speed world with its lower risks

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Re: hydrofoil at max speed limit

Postby foilonfoil » Sun Dec 03, 2017 6:22 am

revhed wrote:
Sat Dec 02, 2017 8:53 pm
Peter_Frank wrote:
Sat Dec 02, 2017 6:59 pm

But no, there is no speed limit for a given foil

It is not drag that is the limiting factor for speed, nor the kites max speed (such a thing does not exist either, just as a hydrofoil can not have a max speed)

But it is not so, there is no max speed...

8) PF
:nono:
So simply NOT true, EVERYTHING has a max speed limit, as far as we know now most mass is a little under light speed!
Therefore read literally as posted in 3 (three) different sentences above are FALSE!
And back to reality,
By using more and more power to get a draggy, any, foil to go faster you WILL reach its max speed limit when it breaks, YES, due to drag!
So in the real world one CAN say a given KBHF set up DOES have a general max speed based on wind strength, kite size, rider skill, its build strength, which if we really wanted could be determined.
BTW, the same logic may be applied to kites which also have a real world max speed due to drag and breakage!
R H
Totally agree. The the amount of power needed to overcome a draggy large foil becomes impractical. On the water you just can't go faster and you can feel the drag in the foil slowing you down.

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Re: hydrofoil at max speed limit

Postby plummet » Sun Dec 03, 2017 8:25 am

Peter_Frank wrote:
Sat Dec 02, 2017 9:51 pm
Against stupidity even the gods themselves struggle in vain :roll:
I think Peter is missing the point of the question.
Its not discussing theoretical physics and the maximunm speed that can be obtained if all practical limitations are removed. Its asking for real world top speeds.

I see 3 common outcomes.

1) You reach the top speed of your equipment and cant go any faster. That's the best out come.
2) Increased lift due to speed and stabilizer angle drives you out of the water, no matter how hard you stomp on the nose, leading to violent and immediate smack down,
3) Ventilation down master or wing breach leads to lost of lift that might be recoverable or might lead straight to instant smack down.

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Re: hydrofoil at max speed limit

Postby Peter_Frank » Sun Dec 03, 2017 11:33 am

plummet wrote:
Sun Dec 03, 2017 8:25 am
I think Peter is missing the point of the question.
Its not discussing theoretical physics and the maximunm speed that can be obtained if all practical limitations are removed. Its asking for real world top speeds.
Snip...

Am I missing the question here ? Maybe, but the full quite interesting question was:
slowboat wrote:
Fri Dec 01, 2017 11:39 am
Obvious beginner question: What happens when you push a foil beyond its maximum speed?

And to his question some of the answers are IMO

1. A given foil does not have a maximum speed, it only has a typical practical max speed that only the good riders get past.
2. It will not break nor cavitate, at the speeds we are talking about here.
3. It is a lot more difficult to ride at high speeds, a lot more kitepower and stabilizer needed, and you wont get to the same speeds as smaller and more flat wings.


To slowboat: No risk or anything drastic will happen when you push a well trimmed foil beyond a by some labelled "maximum speed" (as no such thing exist...) at the real world speeds we are talking about here.

Maybe I missed it, but I found the question quite obvious - as so many seem to have labelled a "max speed" for a given foil, that now many actually think there is a definite max speed you should not exceed, and curious to what happens if you go even faster ?

It should be called typical max speed nowadays, then it all makes sense :thumb:

I am not talking about theoretical physics here, but real life physics :D

And after reading your post about a foil that "dives" when you go faster - your question might origin from that slowboat ?
Just a thought :rollgrin:

8) PF

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Re: hydrofoil at max speed limit

Postby slowboat » Sun Dec 03, 2017 12:15 pm

Peter_Frank wrote:
Sun Dec 03, 2017 11:33 am
plummet wrote:
Sun Dec 03, 2017 8:25 am
I think Peter is missing the point of the question.
Its not discussing theoretical physics and the maximunm speed that can be obtained if all practical limitations are removed. Its asking for real world top speeds.
Snip...

Am I missing the question here ? Maybe, but the full quite interesting question was:
slowboat wrote:
Fri Dec 01, 2017 11:39 am
Obvious beginner question: What happens when you push a foil beyond its maximum speed?

And to his question some of the answers are IMO

1. A given foil does not have a maximum speed, it only has a typical practical max speed that only the good riders get past.
2. It will not break nor cavitate, at the speeds we are talking about here.
3. It is a lot more difficult to ride at high speeds, a lot more kitepower and stabilizer needed, and you wont get to the same speeds as smaller and more flat wings.


To slowboat: No risk or anything drastic will happen when you push a well trimmed foil beyond a by some labelled "maximum speed" (as no such thing exist...) at the real world speeds we are talking about here.

Maybe I missed it, but I found the question quite obvious - as so many seem to have labelled a "max speed" for a given foil, that now many actually think there is a definite max speed you should not exceed, and curious to what happens if you go even faster ?

It should be called typical max speed nowadays, then it all makes sense :thumb:

I am not talking about theoretical physics here, but real life physics :D

And after reading your post about a foil that "dives" when you go faster - your question might origin from that slowboat ?
Just a thought :rollgrin:

8) PF
Correct!

(Sorry if my original question was not worded well. I am experiencing some instability as I speed up and was wondering if this was due to me approaching my foil's "max. speed" or some other reason (such as improper tuning or just inadequate skill))

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Re: hydrofoil at max speed limit

Postby Peter_Frank » Sun Dec 03, 2017 12:20 pm

:thumb:


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