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How to turn a hydrofoil - and what is YAW ?

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

Postby plummet » Mon Dec 11, 2017 6:50 am

Interesting thoughts. My take is a little different.

Yaw control to me Is very similar to other sports as far as i'm concerned. What is different is the weight distribution and height control. I lean in and "yaw" every time I turn my mountain bike. The technique is different. The balance point is different but the principle is the same. Same goes for long board skating and the feeling to is also similar to running down the line on a way. I'm not heal/tow edging as a primary turning method I'm leaning/yawing.

Your comparison to a unicycle is apt and probably closer sensation. Similar too is a wheelie on a bike. What the bike/unicycle is lacking is the height control,

To me height control is the key difference, you need to lean in whilst maintaining even balance and affecting.

I think the balance point is the single biggest issue to over come. With most other boards sports (can bikes for that matter) you can be relatively course in with your balance point it doesn't really matter if your feet are 50/50 or 60/40. It matters a huge amount on the foil. It takes time to sort that balance point and unlearn the bad habbits that you have learnt over the last X amount of year!......

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

Postby MattyM » Mon Dec 11, 2017 11:12 am

Peert wrote:
Sun Dec 10, 2017 10:48 pm
Hi Peter.
Thanks for taking these efforts. Clear Explanation.

One comment.... I would think the term YAW doesn't come from aviation as it is also used in the maritime environment. Since boats are around a couple of thousand years longer than planes it must originate from our beloved environment.
odMH9.gif

you: "This term is new to many, and also origins mostly from aviation and not a commonly known expression amongst most."
Thanks for that diagram Peert- I've learn two new terms - Surge and Sway! (I know about heave from the ground rising when you cut down a tree and water gets back into the soil.)
Last edited by MattyM on Mon Dec 11, 2017 3:25 pm, edited 1 time in total.

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

Postby Kamikuza » Mon Dec 11, 2017 1:50 pm

Peert wrote:
Sun Dec 10, 2017 10:48 pm
Hi Peter.
Thanks for taking these efforts. Clear Explanation.

One comment.... I would think the term YAW doesn't come from aviation as it is also used in the maritime environment. Since boats are around a couple of thousand years longer than planes it must originate from our beloved environment.
odMH9.gif

you: "This term is new to many, and also origins mostly from aviation and not a commonly known expression amongst most."
Heave . . . such an apt name :D

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

Postby revhed » Mon Dec 11, 2017 2:35 pm


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

Postby Peter_Frank » Mon Dec 11, 2017 3:20 pm

revhed wrote:
Mon Dec 11, 2017 2:35 pm
viewtopic.php?f=196&t=2385306&hilit=yaw
R H

Amazing, very well remembered Revhed :thumb:

It was 3½ years ago, but with a lot of words only without simple illustrations it is not easy to understand for newbees, this is why I made a new updated one :naughty:

8) PF

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

Postby Peter_Frank » Mon Dec 11, 2017 3:49 pm

Thank you :D

- and I am sure you are right Peert, it origins from sailing of course, even if used most often in aviation now, my mistake.

My background in flying and aerodynamics/design, and the fact that when you google it today (just checked) yaw is mostly used in aviation, made me erroneously think it originated from this :wink:

8) Peter

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

Postby Mossy 757 » Mon Dec 11, 2017 5:27 pm

Yaw is not what turns a hydrofoil, rolling in the direction of turn redirects the upwards lift vector towards the inside of the turn and induces the change of direction.

Just like stepping on a rudder pedal in a plane doesn't change direction, only points the nose in a new direction. In a plane when you want to turn, you roll the plane so that the lift vector propels you in the new direction and use yaw to keep your altitude through the turn.

Not to just find a reason to disagree, but like literally everything in this thread is technically wrong from a physics perspective. It's the lift vector that creates direction change, not the ability to "push' the foil into a yaw moment with your feet and hips.

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

Postby Peter_Frank » Mon Dec 11, 2017 6:00 pm

Mossy 757 wrote:
Mon Dec 11, 2017 5:27 pm
Yaw is not what turns a hydrofoil, rolling in the direction of turn redirects the upwards lift vector towards the inside of the turn and induces the change of direction.

Just like stepping on a rudder pedal in a plane doesn't change direction, only points the nose in a new direction. In a plane when you want to turn, you roll the plane so that the lift vector propels you in the new direction and use yaw to keep your altitude through the turn.

Not to just find a reason to disagree, but like literally everything in this thread is technically wrong from a physics perspective. It's the lift vector that creates direction change, not the ability to "push' the foil into a yaw moment with your feet and hips.

You are correct the turn itself AFTER the initation by means of yaw and leaning and kite, is held in a curve by the lift going towards the center of the turn now, but this is simply a following effect of the leaning and kitepull and yaw movement and no reason to make it more complicated than necessary, for those who want to learn to turn :naughty:

K.I.S.S.

And the ability to push the foil into a yaw moment is definitely the major part of how fast and tight you can carve, together with leaning inside in sync and using the kite :thumb:

The thing is, that this very yaw move is what is missing when we learn to foil and want to turn, everything else comes quite fast, except this which is not natural from other boards.

8) PF

PS: Stepping on the rudder pedal actually turns the plane quite a lot, even with level wings.
This is the reason why we use the ailerons to bank our gliders in the opposite direction of the rudder, so we go straight when we slideslip for a landing if brakes are missing.

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

Postby Mossy 757 » Mon Dec 11, 2017 7:20 pm

Stepping on the rudder turns the nose but it doesn't change the direction of the plane in any meaningful way when compared to doing an aileron roll and pulling back on the stick to deflect the elevators.

I get that what you're trying to do is define a term in ways that your average beach goer will understand, but to me it's not helpful to incorrectly explain something because you suspect your intended reader won't know the difference.

And no, turns on a KBHF don't initiate with a yaw moment, they initiate with you pulling against the kite to roll the board in the direction of the turn. The forces available due to strut deflection between footstraps and fuselage would be entirely insufficient to maneuver a KBHF without the added forces that come from the lift vector of the front wing. Maybe another way to say that is if you're maintaining that rider "yaw input" is what initiates direction change, then you need to demonstrate through vector math how a rider would even go about providing that input. Foils by design don't deflect in the direction of yaw, so while they do yaw in the sense that the nose of the board travels through many degrees of angular change during a turn, it's not because of rider input against that axis of rotation.

When a noobie fails to appropriately control power in the kite, they get stuck in the "start to roll away from the kite" phase with the kite too low and they power up significantly, therefore creating a runaway situation in a straight line. This is why you see the pros bring their kites VERY high at the leeward gate of a race, they're reducing the amount of horizontal power the kite creates, thus allowing them to roll away from the kite and initiate the turn. If they held the kite low and tried to roll upwind to start a turn, the kite would simply power up as the line tensioned and built speed because they wouldn't have the necessary force to roll the front wing upwind, the power vector of the kite prevents the front wing from driving upwind to make the turn happen, when you depower the kite (by bringing it high or sheeting out) you're able to let the front wing lift against the kite traction and therefore make the turn happen.

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

Postby revhed » Mon Dec 11, 2017 8:22 pm

For any of those who can skillfully fly facing stance forward try this.
DSC01880.JPG
Sorry VERY old photo but the only foward facing stance example I could find.
Use ONLY yaw input and note what happens, twist body, feel yourself induce by pushing one foot forward and the other back with NO weight change.
Use ONLY left, right weight changes, NO yaw, note what happens.
Combine both and feel what happens.
Do this while doing slalom AND carving turns.
I will be interested to read what others think happens.
By using facing forward stance pitch input is limited and seems because of this one is MUCH more able to input ONLY roll and, or yaw, or both
and really know that you are doing this.

R H


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