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hydrofoil at max speed limit

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edt
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Re: hydrofoil at max speed limit

Postby edt » Fri Dec 01, 2017 6:28 pm

It depends on shape of foil. you know when you hit max speed for that shape because you feel the foil dragging. like when you drive a truck 100 mph this wall of air slams you can't go faster. rocket has a really low top speed below 30 mph but race foils can do 50 mph. right now the top speed limit for kiters on foils is mostly fear. we have small foils that can hit in excess of 50 knots 55mph. my next foil will be high speed.

based on foil sailrocket speeds max speed before cavitation ruins lift is in excess of 65 knots or 70mph

you want to go there be my guest. so far nobody wants to test the limit and by test I mean crash a foil at 71mph get up after the crash and say Yup 70 was the limit after all. Its bound to happen I think

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Re: hydrofoil at max speed limit

Postby Mossy 757 » Fri Dec 01, 2017 7:54 pm

plummet wrote:
Fri Dec 01, 2017 6:23 pm
Mossy 757 wrote:
Fri Dec 01, 2017 5:12 pm
davesails7 wrote:
Fri Dec 01, 2017 3:09 pm

In the end, I think the speed limiter for most is fear of crashing.
Do you think that the kites are the limiting factor for top riders? Like if Nico had a kite that could easily do 60 knots, would the foil follow along happily?
No. The limiting factor us not the kite. Snow kiters and kite buggiers hit 50-60+ knots with fairly low spec kites.

I have personally done around 50knots in my kite buggy on an old 10m edge. I've done been 45-50 knots on my 8m catalyst and 6m Reo!

Oh yeah, duh, Alex Caizergues just did 59 knots with a Diablo...well, in that case, what do you think the top speed of modern race kites is and do you think LEI's can have a higher top end in the highest wind conditions?

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Re: hydrofoil at max speed limit

Postby revhed » Fri Dec 01, 2017 8:03 pm

plummet wrote:
Fri Dec 01, 2017 6:17 pm
Each foil has a maximum top speed for its given set up.
By adjusting the stab to lol aoa ive increased that upper limit by at least 20%!
:thumb:
R H

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Re: hydrofoil at max speed limit

Postby revhed » Fri Dec 01, 2017 8:07 pm

Mossy 757 wrote:
Fri Dec 01, 2017 5:12 pm
Do you think that the kites are the limiting factor for top riders?
NO!
The foil, YES!
Nico is talking much smaller F wings and stabs needing of course much more board speed before lift off but should be faster in the control of
ballsy quick young athletic pilots like him!
RH

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Re: hydrofoil at max speed limit

Postby alexrider » Fri Dec 01, 2017 11:39 pm

They will never go fast as a speed board.... No reason why they wouldn't one day. Drag is what ultimately limits speed.
or jump higher than a twintip... No reason why they wouldn't. Easier for the average foiler to go ballistic than the average TT rider.
or surf better than a real surf... Depends how you define real surf. Check videos of what certain foil riders do on waves.
but foil win in light wind always.... Agree on this one. :thumb:
kiterocky wrote:
Fri Dec 01, 2017 5:59 pm
They will never go fast as a speed board....or jump higher than a twintip...or surf better than a real surf...but foil win in light wind always....

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Re: hydrofoil at max speed limit

Postby foilonfoil » Sat Dec 02, 2017 2:15 am

Based on my own experience - Larger wings/masts will just stop going fast (aka big wing MHL Lyft) ... There is a physical limit you will hit. Many of the higher performance foils will generate increasing lift at higher speed and you get to the point you are working very hard with considerable front foot pressure to keep the foil in the water.

Downsizing front wing will provide higher top end at the expense of bottom end performance.

My own top speed is just over 30mph and anything higher just became unstable as front foot pressure increased. I have a new foil and need to test its top speed. I spent a short time on a small AlpineFoil "Channel Crossing" wing designed to go fast in one direction... It was very fast (greater than 30mph+ but I was not wearing my GPS) and stable but cavitated at low speed so not really practical for all round use.

As a warning, you can really hurt yourself at these speeds.

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Re: hydrofoil at max speed limit

Postby revhed » Sat Dec 02, 2017 8:44 am

alexrider wrote:
Fri Dec 01, 2017 11:39 pm
They will never go fast as a speed board.... No reason why they wouldn't one day. Drag is what ultimately limits speed.
or jump higher than a twintip... No reason why they wouldn't. Easier for the average foiler to go ballistic than the average TT rider.
or surf better than a real surf... Depends how you define real surf. Check videos of what certain foil riders do on waves.
but foil win in light wind always.... Agree on this one. :thumb:
kiterocky wrote:
Fri Dec 01, 2017 5:59 pm
They will never go fast as a speed board....or jump higher than a twintip...or surf better than a real surf...but foil win in light wind always....
So nice to read progress in understanding of our beloved sport toys! :thumb:
As for speed, shorter, thinner, stiffer, stronger, STRUTS, with tiny wings, flown by a super human pilot in a strong steady wind on a flat H20 spot,
may go much faster than we imagine now! :idea:
R H

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Peter_Frank
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Re: hydrofoil at max speed limit

Postby Peter_Frank » Sat Dec 02, 2017 6:59 pm

Most of you are wrong here...

Of course there is a "practical" speed for a given hydrofoil that is difficult to go beyond, yes, and this is why smaller and less lifting wings will be able to go faster.

But no, there is no speed limit for a given foil (if we look away from the cavitation issues at higher speeds).

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) - it is the kite power that limits !

How to explain ?
Easy - take a given huge draggy foil, pull it after a big superpowered speedboat, and now you will be able to get the foil to crazy high speeds, using sheer power :rollgrin:

The same with a kite - 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.

As said, there is a practical limit where it feels like you can not go any faster, but this is solely because you have relatively limited power available when kitesurfing.

So it might seem like a given wing and foil setup has a max speed - and this is how it feels in real life out there because the drag is squared with your riding speed so the draggy ones will feel like anchors quite fast, and because of control issues it will also be harder to ride.

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

The draggy foils demands a lot more power to get to the same speed, but they CAN obtain the same speed as low drag foils, if sufficient power.

This is the reason why really good riders like Gunnar, can obtain a lot higher speed when riding say the Takuma wing, than most other riders who cant.
It is individual and depends on how much force you can get from the kite, thus it depends hugely on skill and wind strength.

8) PF

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Re: hydrofoil at max speed limit

Postby gbrungra » Sat Dec 02, 2017 8:12 pm

Sail Rocket used super-cavitating foils to go 65 knots. I don't know of anyone who has made them work on a KBHF.

Another limit is ventilation. For instance, Sail Rocket used a "collar" foil around its vertical section(equivalent to a KBHF mast) to prevent the ventilation propagating down the foil. I haven't seen anyone try a similar setup on a KBHF, but I expect someone will at some point.

Wouldn't a longer fuselage be more stable at speed? Too bad about the additional drag...

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Re: hydrofoil at max speed limit

Postby revhed » 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


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