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How to turn a hydrofoil - and what is YAW ?

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joyrider1
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Re: How to turn a hydrofoil - and what is YAW ?

Postby joyrider1 » Tue Dec 12, 2017 8:25 pm

So much said… Trying to compress

To make the technique more pure, think of an kbhf without the kite, just like a surfboardhydrofoil riding on flat water. With a kite you could somewhat cheat a little bit ;-)

First: (if there`s) No roll, (there will be) no turn without crashing.

Second: the roll is initiated by the yawing/twisting of the riders body. Important note: on the water your feet don’t have a stable anchor, so if your upper body is yawed/twisted clockwise, then your lower body is twisted anticlockwise (actio = reactio)

Third: Try to imagine how the riders center of gravity (hip/belly button) is travelling in a straight line and by twisting his body the mast/strut points out of the direction your body is travelling. Thus the mast/strut is led sideways underneath (!) your body. This happens in a very tiny fraction of a second. You are starting to “fall” sideways. To prevent the total “fall” or crash you have to twist a little bit backwards …..

Finally: on a kbhf the mast/strut acts like a rudder. Mast/strut is almost as effective sideways as the wings act like “rudders” for the pitch.

Countersteering initiates the turn. Not more, not less….. Is valid for so many sports…. (skiing, snowboarding, unicycling etc.) You just don’t feel it…………………….

J.

joyrider1
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Re: How to turn a hydrofoil - and what is YAW ?

Postby joyrider1 » Tue Dec 12, 2017 8:32 pm

Go there http://kitehydrofoil.com/how.html “Controlling roll”. Very nicely explained. By “steering” the nose of the board he just means using the twist/yaw.

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Re: How to turn a hydrofoil - and what is YAW ?

Postby Kevin Brooker » Tue Dec 12, 2017 9:21 pm

We impart yaw by pulling against the kite. If we just twist the yaw will be imparted until we try to realign ourselves ( untwist) when it will return to the pre twist state. This is what happens to the astronaut. On a surfboard we twist and roll the board which now tries to move under us giving us balance. Think of it as balancing a broom with the brush up and the tip of he handle in the palm. If we lean the broom and sweep our hand around the broom will stay. The movement of the sweep keeps the cg in a place where we become stable. To change direction we must move the cg back over the board or we crash. We move the cg by turning tighter so the forward speed puts us forward. We have beachwards movement and a vector. To get back over the board we make the two vectors ( beach and turn) converge and we are back on top ready to do something else. On the HF we use the kite to pull against so we have a counter force to just plain twisting. The rudder effect of the mast is minimal cause it itvwas strong a yaw will tank the board out from below us. If we roll we lean and the pull of the kite is the wrench we use for leverage to remain upright. If we yaw away from the kite to windward and do not roll/lean to windward we will get tanked off be leeward side of the rig. Turning a HF is a complex balance of balancing a lot of force vectors. Simple yaw will not do it.

joyrider1
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Re: How to turn a hydrofoil - and what is YAW ?

Postby joyrider1 » Tue Dec 12, 2017 9:30 pm

Kevin Brooker wrote:
Tue Dec 12, 2017 9:21 pm
We impart yaw by pulling against the kite. If we just twist the yaw will be imparted until we try to realign ourselves ( untwist) when it will return to the pre twist state. This is what happens to the astronaut. On a surfboard we twist and roll the board which now tries to move under us giving us balance. Think of it as balancing a broom with the brush up and the tip of he handle in the palm. If we lean the broom and sweep our hand around the broom will stay. The movement of the sweep keeps the cg in a place where we become stable. To change direction we must move the cg back over the board or we crash. We move the cg by turning tighter so the forward speed puts us forward. We have beachwards movement and a vector. To get back over the board we make the two vectors ( beach and turn) converge and we are back on top ready to do something else. On the HF we use the kite to pull against so we have a counter force to just plain twisting. The rudder effect of the mast is minimal cause it itvwas strong a yaw will tank the board out from below us. If we roll we lean and the pull of the kite is the wrench we use for leverage to remain upright. If we yaw away from the kite to windward and do not roll/lean to windward we will get tanked off be leeward side of the rig. Turning a HF is a complex balance of balancing a lot of force vectors. Simple yaw will not do it.
No!!!!!!!!!!
A surfing KBHF does not have a kite. He only has his body to twist (actio = reactio). Don`t think too complicated.....

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Re: How to turn a hydrofoil - and what is YAW ?

Postby tomtom » Tue Dec 12, 2017 10:21 pm

Just look,

motion study

https://youtu.be/h7XupqFOFSg?t=57

/kite no kite is imo irelevant/

every turn is initiated by yaw

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Re: How to turn a hydrofoil - and what is YAW ?

Postby bigtone667 » Tue Dec 12, 2017 11:08 pm

A bit of heaving and yaw ....

https://youtu.be/eKDCWyxnk-M

Seems to me they both work in unison. Yaw alone doesn't allow me to turn in any meaningful fashion.

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Re: How to turn a hydrofoil - and what is YAW ?

Postby Mitaka » Wed Dec 13, 2017 12:43 am

When making turns with my hydrofoil I can yaw the board and the foil in 3 different ways to initiate a turn:

1. Using the momentum of my upper body I can yaw the foil board using my legs and/or hips. For all of you who can not imagine or understand how this is done here is a good example: (body twisting/rotation initiating disk yaw starts at 1:10).
phpBB [video]


Yawing the board in such a way is best done with a light, short pocket board combined with an appropriate foil (mast, front wing...) - it is really easy and much fun. Of course it could be harder with some foils combined with big, long heavy foilboard.

2. I can yaw the foilboard easier when I use the support of the kite (via the harness or when leaning with my hands on the bar and as a result on the lines). In order to understand more easily how this is done just imagine that somebody is holding the waist of the woman in the previous video clip or that she is leaning agains the wall with her hand. In such a case the woman will be able to yaw the disc easier than using her body only.

3. I can yaw the foilboard even more easier if my kite is turning and pulling me through the turn. I will use the previous clip again for easier understanding - imagine that the woman is just standing on the disk and somebody, holding her waist or hand, starts to rotate around the disk - of course the woman together with the disk will also start to rotate (disk yaw).

If you watch some video clips of Kai Lenny or anybody else hydrofoiling without kite you will clearly see how they jaw the board to initiate turns only using their bodies and if you watch (as already suggested) some Cloudfoilig clips you can see yawing the board using the kite for support or following it through the turns.

In order to keep my balance when hydrofoiling I also control the pitch of the board (in order to control the height) and I roll the board in two cases:
1. I roll the board to the inside of the turn in order to compensate the centrifugal force - the faster I move or the tighter I turn, the more I lean.
2. I roll the board when I foil upwind and I lean against the kite in order to withstand the pull from the kite.

People have difficulties to turn the hydrofoil because of 2 main reasons:
1. Wrong roll control. Either they try initiate the turn by rolling the board and they loose balance or they turn the kite but can not compensate the centrifugal force during turning with correct board roll, they loose balance and fall. I will use bicycle analogy to explain this. If you lean the bicycle without steering in the same direction you will fall. If you steer the handle bar to make a turn and you do not lean enough/or you lean too much to the inside - again you will fall.
2. Wrong pitch control during the turn. Most kiters are used to apply more back foot pressure when turning and even when they manage to foil in straight line with correct pitch control they instinctively lean to the back foot when they start to turn and of course they fall.

To summarise how I understand turning the hydrofoil - I yaw the foil board in order to initiate the turn and I control the roll of the board (in order to compensate the centrifugal force) together with the pitch of the board (in order to control the height). :D

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Re: How to turn a hydrofoil - and what is YAW ?

Postby Kevin Brooker » Wed Dec 13, 2017 1:26 am

Joyrider1. I missed the surfing part and readout as w/ kite. I'll concede the act of trying to imitate a turn by trying to impart yaw is correct but pure yaw will not turn.

Mitaka had a much clearer explaination then mine and thanks.

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Re: How to turn a hydrofoil - and what is YAW ?

Postby plummet » Wed Dec 13, 2017 8:04 am

The more I think about this the more I disagree that yaw is the primary turning function of the foil. I was out today on the mutant boosting and watching myself yaw the board aggressively multiple times. I was doing this well before foiling and my yawing experience did not help me on the foil.

So. Yaw input is not the primary turning mechanism of a hydrofoil. Much like yaw is not the primary turning mechanism of an aircraft.

My take on this is that you must pitch, roll and yaw seamlessly and in unison to make an effective foil turn.


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Re: How to turn a hydrofoil - and what is YAW ?

Postby revhed » Wed Dec 13, 2017 8:27 am

plummet wrote:
Wed Dec 13, 2017 8:04 am
you must pitch, roll and yaw seamlessly and in unison to make an effective foil turn.
Enough said and well proved to myself doing forward facing stance flying. :thumb:
As for counter steering,
There is no roll moment caused by gyroscopic precession when flying our KBHFs!
https://en.wikipedia.org/wiki/Countersteering
Interesting to note no mention of ANY board sports?
I swear again by flying facing forward that I am NOT counter steering, either yaw only, roll only inputs, might be wrong I will admit but think not.
R H


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