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 Post subject: How do you turn a hydrofoil ?
PostPosted: Mon Jun 23, 2014 11:29 pm 
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Hi all

Think we should make a thread of its own on this topic, as it seems many dont agree at all (actually noone agree with me it seems :roll: ), but l think we are all openminded so lets discuss thoughts and experiences.


My take on how it works:

When going halfwind or upwind, the board is angled to windward.
We have a force vector from the kite, up, plus the force from the lifting front foil wing up.
These has to balance the weight of you (and your board), nothing more nothing less.

But when the wing is tilted, it also have an upwind force.

This has to be balanced exactly by the kite downwind force (and the kite forward force is balanced by the overall foil drag).

Then we have the steady state where we ride balanced.

If we have the board tilted like this, and suddenly let go of the kite - what would happen ?
Two things can happen - we could fall backwards into the water, OR, we could initiate an upwind turn by twisting, thus making an arc as long as the foil will keep foiling.

Meaning, when a turn is started and the foil is tilted, we can make an arc or circle, simply because the force from the wing going "inside" the turn, is equalled by the centripetal force.

Nothing new about this :thumb:

But my experience and thoughts are, that because you (well, your feet) are elevated 105cm above the wing and center of effort, heel or toepressure has no noticeable effect at all.
On a surfboard, toe and heelpressure will directly change how much the board is "tilted" right away, so the feedback is immense and you turn on a dime just by putting a little pressure on your toes f.ex.
This does not hold for a hydrofoil, because your feet are more than 1 meter away from the wing, IMO.
The wing is self stabilizing - why is this ?
Because, if it starts to roll or fall to one side, the inside wingtip will experience a greater AOA, and the outside a decreased AOA, thus immediately creating an correcting force/moment that will stop this roll - GREAT, and this is why a foil is stable and does not immediately fall to one side or the other.

Okay, when we ride straight in balance, we have equilibrium.

To make a turn into a narrow jibe or turn, we lean forward (inside) and twist the board at the same time.
Leaning forward and accelerating a sharp turn, is improved greatly by flying the kite to the other direction, thus we get a sudden pull which can help us both lean forward and twist the board into the sharp turn :thumb:

When into the turn it goes automatically, so no biggie apart from balancing yourself (which is hard to start with).
When we want to turn back upwind from a full downwind turn f.ex, we use the opposite method - we sheet the kite OUT when we carve upwind to drop the pull, thus we lean back and turn upwind.

Of course we use toe/heel pressure all the way for balancing and fine corrections - but IMO every big change of direction/turn is initiated by a twisting motion (yaw), and not by pressure on the toes or heels.

I might be wrong, but this is my experience, and when I think about it, it also makes sense.
Unfortunately it is also the reason why it took me so long to learn - as the well known toe/heel balancing and turning on a surfboard, does not work on a hydrofoil IMO :wink:

8) PF

PS: Came to think about Joyriders example with a bike.
Here you balance and can lean into the turn, thus accelerating the turn.
If you stood up on the bike on a plate on the seat, hands off the handle, you could still turn by doing weight shifts.
But you dont really turn anything directly, by using toe or heelpressure, as you are 1 meter or higher above the ground.
If you used the handle to turn though, while leaning inside - you can turn sharper than if just balancing and leaning inside.
This could maybe be compared to using/initiating with a twisting/yaw motion on a hydrofoil - and as we got the kite pull to counteract both ways, we can be quite agile in turning/arcs compared to what one would think :naughty:
Of course it is two different principles of balancing and turning, but point is that you dont really apply any direct turning force by using heel or toepressure when so far away from the contact point.


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 Post subject: Re: How do you turn a hydrofoil ?
PostPosted: Tue Jun 24, 2014 9:23 am 
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Hi Peter,

"IMO every big change of direction/turn is initiated by a twisting motion (yaw) and not by pressure on the toe and heals."

Are you saying that you are sliding the board into the turn as opposed to carving as on a surfboard?

Keep up the great discussions.


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 Post subject: Re: How do you turn a hydrofoil ?
PostPosted: Tue Jun 24, 2014 11:37 am 
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P F WROTE on another post,
Hmmm, curious about this, as I dont see this happening with the foils I've used ? (Zeeko and Takoon and a Spotz shortly)

These dont turn at all if I put pressure on my toes or heels when up foiling (and a foil should not, as it stabilizes itself in the upright position).

They turn when you make a twisting motion only.

But maybe you indirectly gain some ability to ride more "powerless" and not putting pressure on the front versus back foot, and balance yourself using the kite, if practising on a non foil raceboard and trying not to use heel-toepressure at all ?
It might work - but I think the most important thing is to learn to ride the kite very powerless and sheeted more out than usual, which you might practice by using a raceboard and trying to balance without foot pressure.

I can easily put my front or rear foot further towards the lee or windward side of the board - and it wont really turn doing this.
(but I will lose my balance and leverage when I turn for real and have to turn back, so not good of course, and the trim somehow just feels "bad" in every way)

As said before - the fact that a hydrofoil is balanced by itself regarding the "tilt" of the mast, makes the ability to sheet the kite in/out AND the ability to turn the board downwind/upwind by twisting - the reason why it takes so long to get it under your skin and be natural.

It is not something that is known from other sports as far as I know - although you CAN turn boards this way to some degree in f.ex surfing (or skateboarding), where you can pump the board by doing the twisting motion, where the board nose actually turns left and right of course.
But with these boards, you can also turn by using pressure on the edges meaning toes/heels (which is done when carving/turning fuller circles).

Posting this, as it seems that we are some who disagree a lot about this very topic ?


My statement is, that you dont turn a hydrofoil by putting pressure on your toes or heels (or leaning forwards/backwards which is the same).

You turn a hydrofoil by twisting, giving the yaw motion that turns it (making it curve/carve) :naughty:

I am quite sure of this actually, but might be proven wrong and open for this to happen.

Agree with the added dimension, being one serious reason also, why we dont just do it right away :rollgrin:


An amazing sport in every way :thumb: AGREE OVER AND OVER!!!

8) PF


Peter_Frank wrote:
joyrider1 wrote:




These dont turn at all if I put pressure on my toes or heels when up foiling (and a foil should not, as it stabilizes itself in the upright position).

They turn when you make a twisting motion only.




Posting this, as it seems that we are some who disagree a lot about this very topic ?


My statement is, that you dont turn a hydrofoil by putting pressure on your toes or heels (or leaning forwards/backwards which is the same).

You turn a hydrofoil by twisting, giving the yaw motion that turns it (making it curve/carve) :naughty:

I am quite sure of this actually, but might be proven wrong and open for this to happen.


8) PF


Ok Peter, I will attempt to prove you wrong only because of your above statement, respectfully!
And hopefully to help others understand my thoughts on turning a kiteboardhydrofoil.
I post this photo to help prove my point.
Attachment:
DSC01880.JPG
DSC01880.JPG [ 3.58 MIB | Viewed 93 times ]

It is extreamly clear to me that when I do a flying turns in this stance that I change foot pressure and the same goes when you do any turn in any stance.
I like you am open for dispute in the sake of learning but I am sure of this.
You need to put the kite where it will pull you thru the turn, at least in a jibe, a tack is a little different.
I feel I turn the kite up or down and wait until it starts to pull in the other direction then APPLY foot pressure on the down wind rail for a jibe and carve thru the turn.
Of course there is different timing for different wind speeds and turn radius.

I feel strongly that the turn happens when the STRUT, not MAST (see wikipedia for definition)
passes thru the vertical to arrive in the oppsit angle after the turn. Roll input!
There must be a time when the strut is vertical and twisting alone can never make this happen.
The only way for this to happen is by applying weight on the rails to bring it up to vertical!
Twisting when not appling rail pressure will do very little to make a turn.
I believe the twisting to bring yaw rotation may play a role but a small one, and now that I think about it very little.
I will pay close attention to this my next session.
R H
By the way for anyone wanting to find the center of lift on any foil, flying toes forward will quickly narrow it down!

JOYRIDER WROTE;
My thoughts about turning a foilboard:

Generally every weight-steered vehicle that is unstable in rest and stable in movement seems to need a change of roll angle to make a stable turn/curve in an orbital way.
AGREE
This is the case for example for: Biking, motor biking, snowboarding, skiing, unicycling, deltagliding, skateboarding, even waveriding and a lot of other sports as well. A foilboard is such a “vehicle” as well.
The straight stable movement forward needs to be broken down. Only if the weight center has been moved away from the center aside, the roll angle can be created.
AGREE
For example a bike going in a straight stable direction needs to turn the handle bar for a very short moment into the wrong direction.
DISAGREE
Following this the vehicle will start to “fall” into the direction it actually wants to turn to and creates a roll angle to this direction.

This is valid for a kitefoil as well. First you have to create a roll angle by pushing your heels or toes for a very short time to the “wrong” side. By this having created enough weight shift/roll angle towards the "right" side you can afterwards push the “right” side of the board/foil and the turn into the intended direction can begin.
DISAGREE WITH WRONG SIIDE, BUT AGREE WITH ROLL INPUT ABSOLUTLY NEEDED!

The ride in this video http://vimeo.com/91188392 only can be done by executing the above said (?). You can almost see how he changes the roll angle first and secondly being able to turn.
Twisting might only have a very little aspect in this. It more seems to help creating the roll angle? Yaw movement alone seems to be overestimated?

But: If you have a kite that you can hold onto, this all might be a little different because you can deliver a momentum towards the board against a stable “anchor” (the kite). This might change the game (a little bit).

Interesting because all this happens automatically all the time… More interesting: how can you give beginners like me translated advice or “pictures” of all the theory.

My 02cents in the evening
j.
R H;
I like his thoughts except for this,
First you have to create a roll angle by pushing your heels or toes for a very short time to the “wrong” side.
I do not apply any more weight to the upwind rail ever before I do a down wind jibe, unless you want to slow down before the turn which I do often, but this is not the same as talking of the turn itself.

For example a bike going in a straight stable direction needs to turn the handle bar for a very short moment into the wrong direction. Following this the vehicle will start to “fall” into the direction it actually wants to turn to and creates a roll angle to this direction. (If the rider would continue the first movement of the handle bar the bike would fall completely to the ground.

Thanx joy rider just went for a bike ride and now I disagree with you even more, sorry.

I just rode my bike with no hands and to turn it was 100% roll input meaning weight shift with NO weight being applied in the wrong direction before turning in the direction you wish.
BUT yes ROLL input did it all!
And the same goes for a turn with your hands controlling the turn.
Try to turn your bike with no hands using only yaw, twist input. this also does not work.
Of course there no pitch input when riding a bike on the flat.
And when you do a bike turn with the handle bars you "catch yourself from falling by turning the bars.
And no roll input ,no turn!
So thanx for the hands on bike turn experiment, I learned that it is all roll input followed by yaw input via the handle bars.
BUT, nothing to do with a kiteboardhydrofloil as a bike has gyroscopic effect!
Now off to ride my unicycle to feel how it turns........
Wow thanx J R because I never really thought about how a unicycle turns!
I find that it is almost all YAW input!
I can do 360° spins and for sure that is all yaw input.
But traveling forward turns also need roll input as well.
There is an element of roll and pitch but I feel it is almost all yaw.
Back to the specific question,
I will go fly this afternoon facing forward and test the yaw only theory and report what I feel.
Thanx P F for most interesting thread!
Maybe though we will have to agree to disagree?
R H


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 Post subject: Re: How do you turn a hydrofoil ?
PostPosted: Tue Jun 24, 2014 12:32 pm 
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What I understood so far:

„Countersteering“ seems to be the name oft he game. No matter if riding a bike or a surfboard or a hangglider or snowboard or ......

Anything that supports the countersteering is of advantage, just like
    the initial yaw
    the change of the pull of the kite
    the pressure on heel/toe letting the vehicle go for a little moment of time into the “wrong” direction
    or mostly a combination of all these

Couldn`t find examples for watersports but basically its the same. AND: At low speed of a bike you can ignore the gyroscopic effect.

https://www.youtube.com/watch?v=PgUOOwnZcDU
https://www.youtube.com/watch?v=OLzB5oriblk
https://www.youtube.com/watch?v=HrK_UsbsSro

The main curving has to be done like it is shown in these videos by bringing the center of gravity to the inside of the intended curve. Create the “roll angle” or "lean".

These principles seem to be unignorable. The examples shown with a motorbike are valid for a kiteboard as well. With a kite attached to you just have an additional force, which has to be put into the overall balancing, that`s all.

Even if you made a slowmotionfilm of a waveboard which is going with normal riding speed you could see it as well.

Another example: Unicycling. The rider has to do quite a lot of countersteering to be able to ride. He is yawing into the direction of the intended curve. But mainly to give the tire the possibility to countersteer (action = reactio, long time ago in school :-? ). Thus he creates roll/lean and brings the center of gravity inside the intended curve. I assume that you don’t notice the countersteering like every bike rider in the first moment would disagree on turning the bar into the wrong direction for a little moment. If you filmed yourself unicycling in the way the motorbikevideos are made, frontal view, and tried to make a sharp turn at medium speed, then you should find out.

And one more: A person just walking or running. The more drunk the person, the more the countersteering. Remember myself sometimes :D

And even with a kite trying to make a turn upwind. You sheet the bar – you can lean or “fall” a little bit more upwind OR you countersteer the board– you then can make the turn upwind.

In fact we all are countersteering all the time, I guess we just don`t notice.

And: Same with a kitefoil.

No problem in agreeing to disagree, all the input might help more or less the one or another. :thumb:

Greets j.


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 Post subject: Re: How do you turn a hydrofoil ?
PostPosted: Tue Jun 24, 2014 12:43 pm 
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Peter Frank wrote: "Of course we use toe/heel pressure all the way for balancing and fine corrections - but IMO every big change of direction/turn is initiated by a twisting motion (yaw), and not by pressure on the toes or heels."

Consider the flow over the front wing with its anhedral shape in a steady state glide, no kite. If you yaw to the right, that will cause the board to roll left. This is because the left side of the foil, curved downward is now pushed downward by the water flow (your instantaneous speed is still in the direction of travel, so the water flow is not perpendicular to the long axis of the board/foil). The water flow pushes the right side of the foil up and the left side down. The water is flowing across the foil. It seems to me you must lean in the direction you wish to turn first, then the board will yaw around in that direction. Otherwise, if you yaw first, the board will lean out of the turn.


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 Post subject: Re: How do you turn a hydrofoil ?
PostPosted: Tue Jun 24, 2014 1:28 pm 
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tried reading this but realised I may have Attention Deficit Hyperactivity Disorder :-?


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 Post subject: Re: How do you turn a hydrofoil ?
PostPosted: Tue Jun 24, 2014 3:54 pm 
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I would suggest to think to the dynamic of airplanes.
Turning is a combination of 3 effects: rudder is used for yaw and ailerons are used for roll, the elevator controls the pitch.
In HF you control the yaw by "twisting", the roll by unbalancing your weight (very little with toe&heel pression), and the pitch by feet weight.
Now it's a matter of contribution of the 3 effects.
Ailerons are the primary turning control in planes that have them. it works also with no rudder and no elevator.
Real planes use ailerons for turning and the rudder just dials in the turn better (coordinated turns).
You can easily understand that if the wing plane in very tilted (once you are rolled), you can turn controlling the pitch. I think that's the keypoint.
In acrobatic airplanes the aileron banks the plane and the elevator turns the plane.
So what I experienced is:
1) you unbalance yourself->roll
2) you push your back foot ->pitch
3) eventually make a fine twist->yaw

So, the more you want to turn, the more you have to roll, and the more you have to increase pitch.

Think to a sharp turn, let's say a foiling turn to toeside in 5-10meters radius. You need to push a lot with your back foot while your wings are at about 60°.
Just my 2 enginering cents


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 Post subject: Re: How do you turn a hydrofoil ?
PostPosted: Tue Jun 24, 2014 8:09 pm 
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antonell0 wrote:
I would suggest to think to the dynamic of airplanes.
Turning is a combination of 3 effects: rudder is used for yaw and ailerons are used for roll, the elevator controls the pitch.
In HF you control the yaw by "twisting", the roll by unbalancing your weight (very little with toe&heel pression), and the pitch by feet weight.
Now it's a matter of contribution of the 3 effects.
Ailerons are the primary turning control in planes that have them. it works also with no rudder and no elevator.
Real planes use ailerons for turning and the rudder just dials in the turn better (coordinated turns).
You can easily understand that if the wing plane in very tilted (once you are rolled), you can turn controlling the pitch. I think that's the keypoint.
In acrobatic airplanes the aileron banks the plane and the elevator turns the plane.
So what I experienced is:
1) you unbalance yourself->roll
2) you push your back foot ->pitch
3) eventually make a fine twist->yaw

So, the more you want to turn, the more you have to roll, and the more you have to increase pitch.

Think to a sharp turn, let's say a foiling turn to toeside in 5-10meters radius. You need to push a lot with your back foot while your wings are at about 60°.
Just my 2 enginering cents


Agree :thumb:

Only difference in the order you mentioned 1-2-3, as my experience is that you can turn must faster DOWNWIND and better if you unbalance yourself, and simultaneously make a twist, when possible.
This twist comes naturally, if you just look in the direction you want to go.
And THEN you can push with your back foot to keep the tight circle, when banked.

If we are doing S turns from side to side without switching stance:

You ride halfwind or upwind with kitepull and the kite very low.
When you bank the kite around hard, still down low - it has good pull.
You use this pull for two things.
First it will make you able to put your bodyweight to leeward very fast, to initiate the roll (instead of slow countersteering or similar).

Secondly, you can put immense twist (yaw) on the board because of the pull, where you actually let your front foot follow the kite so to speak, so the turn is really good (tight) and efficient.

Turning this way, you can easily turn with a max kite in the lightest of wind, without downlooping, and still keeping lines tight and able to ride toeside or jibe foiling if you want that, instead of turning back :D

When you have turned half a circle or so, and you want to head up again - you let out on the bar, so you can "drop" backwards with your body (upwind) to start the roll, thus start the curve/turn upwind while pushing with your back foot yes, for a good carve upwind now.
Here, you can not use the twist/yaw as much, because you dont have the same support from the kite, as you want the kite to be as depowered as possible.

Will still say though, that even without any kitepull, yaw is the best way for quick turns, just like on a unicycle :rollgrin:

8) PF


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 Post subject: Re: How do you turn a hydrofoil ?
PostPosted: Thu Jun 26, 2014 5:58 am 
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From another thread :

adseguy wrote:
Yo Bob!

Good points from everyone and I tend to look at it like a physics problem with force vectors everywhere, but in the end that doesn't help for the basics.

The bike analogy is probably the best and closest. You need both roll and yaw in harmony to turn. The thing is that with a regular kiteboard, roll is much more heavily biased and with the foil it's more yaw biased. I've only been out about 5 times and can stay up on the foil for 200 yards plus now. I've realized it's finesse not brute strength that will win. Bob, we have to unlearn kiteboarding, skiing, wakeboarding, snowboarding, etc that all use roll and edge as the primary turn mechanism. Like a bike, you can't turn on a dime with a foil. You need to predict and anticipate. Roll with it if that makes sense. The yaw motion, I've learned, is the key. I personally need to stand-up a little more and relax, but I'm getting there.

I'll tell you what, I'm very mentally exhausted after a 1-2 hour session. It's like trying to tight rope walk, where the big muscles aren't used, but the little ones are. I just need to roll with it :)


Exactly - you experience the same in learning as most of us, and I love your expression "we have to unlearn kiteboarding, skiing, wakeboarding, snowboarding, etc that all use roll and edge as the primary turn mechanism".

As this is IMO basically why it takes so long to master for the experienced boarders :wink:

Have also heard many say, that as soon as they found this "key", doors suddenly opened in terms of progressing faster and being and feeling in control, and able to do everything (still learning slowly though) :thumb:

8) PF


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 Post subject: Re: How do you turn a hydrofoil ?
PostPosted: Thu Jun 26, 2014 5:51 pm 
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Huge thanx to P F and J R! :thumb: :thumb:
Because of your ideas I had a science lab day yesterday both on land and H20.
As for counter steering, On my bike at low speeds I simply did not feel it at all, and also hands off turns,using roll input only.
Nor on my unicycle! Maybe some day we can video to see what is going on?
Cool to see it demonstrated with motorcycle on video though!
If someone who really knows will post, but I have a feeling there is gyroscopic progression going on?
Interesting concepts, still not sure they apply to a kiteboardhydrofoil?
I had a killer KBHF session concentrating on what control inputs did what.
I was amazed to find that in the facing forward stance I could initiate turns using YAW, twist only,
BUT,
I could also do almost the same turns with weight change only, roll input.
These were weaving S turns and not U , carving turns!
And even better feel by using roll input, wieght change rail to rail timed with yaw.
Wow I had fun doing this!
After some time finding the correct weight shift and yaw timing it felt like downhill sking slalom style.
I would have not taken this stance style to this level had it not been for this thread. :thumb:
I also tried to do U turns stance forward YAW only, does not work, I will say again does not work!
I also tried to do U turns stance forward with roll only, does not work!
You must add roll input to bring the strut up to vertical to change direction.
BUT,
I was way wrong about how much yaw plays in all turns!
I will now say that I think it is 50% yaw and 50% roll to do well timed clean carved turns.
Understanding there are MANY variables,foil speed,kite pull,kite turn,turn radius,amount of strut in the H20,and many I am sure I do not know!
The fun comes when you put it all together and do a constant speed, small radius leaned a lot turn with good kite turn timing, what a freaking great feeling!

Someone above also posted that a bike is a mixture of the 2 inputs roll AND yaw, I find this correct.
So so nice you posted this, huge thanks, my turn skill and understanding improved more in 1 session than in a month!
I did both the tightest and largest radius turns that I have ever done, only because I was concentrating on what was happening.
Just like "spotting your landing" when kite board jumping, I realised that "looking into your turn" was very helpfull!
I will say that you can feel control inputs much better in the facing forward stance, try it you will like it!
J R ,I do not feel any countersteering concerning kiteboardhydrofoils, not saying it is not there but I really searched to feel this and did not, as I said if you go upwind to slow down just before a downwind jibe then you may think you are countersteering but you are not.
I tried to go meduim speed and do a jibe and if the concept is really present then at least for me it is very subtile.
But I am also the guy who has unicycled most of my life and I sense absolutly no C S there either, maybe I have a mental block?
I just hope I can do a flying roll tack someday, but for now it looks a long way off!
I say the few guys in the world who can do this are WAY skilled!! Hats off, Bravo!
R H


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