Where is CLR on foil?

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Ian K said..Taking me a while to get those subconscious micro movements dialled in. Can you feel the height of the foil through your feet or do you always need to keep a visual reference?

Good question
Don't think I can feel the foil height through my feet.
My guess is looking ahead 5-10m - my brain is doing a constant subconscious triangulation calculation that determines height.
Peripheral vision is probably also adding to the input.

It's interesting, how many non-flight sports require you to constantly operate in 3D?

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fpw9082 said..

Ian K said..

fpw9082 said..
Dietrcih text:
"every body rotates about the center of gravity, not the COR. The COR is nonsense. The forces relative to the center of gravity produce a moment which forces the body to rotate. Are the moments balanced the board goes straight.In case of non planing the sail force acting at the COE before the cg let the board going downward, the moment is left turning. Is the COE behind the cg the board is going upwind, the moment is right turning. "

Can some one explain his words,that board will rotate about center of gravity???
For me COE in relation to c.g. has nothing to do with board turning.

A body rotates around its C of G when all external forces are removed. But to get it to rotate in the first place you need to apply external forces. It generally only rotates about its C of G once it's released. Think of winding up and releasing a discus. (But you can't ignore wind resistance in a looping windsurfer, they won't rotate around the exact C of G )

"In case of non planing the sail force acting at the COE before the cg let the board going downward, the moment is left turning. Is the COE behind the cg the board is going upwind, the moment is right turning. "

Did you understand his words above,board is not in space!what he want to say??

No I can't follow him. Might be a typo, maybe a quirk of google translate?

Yes that reference also implies aircraft and rockets must rotate about the C of G. I suppose things always like to rotate around their C of G but you can force them not to. Hence the parallel axis theorem. Two tug boats can rotate an oil tanker off the wharf around its stern so there certainly are exceptions. Will have to think about a single force on a rocket for a bit.

en.wikipedia.org/wiki/Parallel_axis_theorem

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Ian K said..
Yes that reference also implies aircraft and rockets must rotate about the C of G. I suppose things always like to rotate around their C of G but you can force them not to. Hence the parallel axis theorem. Two tug boats can rotate an oil tanker off the wharf around its stern so there certainly are exceptions. Will have to think about a single force on a rocket for a bit.

en.wikipedia.org/wiki/Parallel_axis_theorem

here is clear example that boat not rotate about c.g.





look at this 2.0 sail 100% area of sail is in front of foil-mast and board still going straight!!

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fpw9082 said..

Ian K said..

fpw9082 said..
Dietrcih text:
"every body rotates about the center of gravity, not the COR. The COR is nonsense. The forces relative to the center of gravity produce a moment which forces the body to rotate. Are the moments balanced the board goes straight.In case of non planing the sail force acting at the COE before the cg let the board going downward, the moment is left turning. Is the COE behind the cg the board is going upwind, the moment is right turning. "

Can some one explain his words,that board will rotate about center of gravity???
For me COE in relation to c.g. has nothing to do with board turning.

A body rotates around its C of G when all external forces are removed. But to get it to rotate in the first place you need to apply external forces. It generally only rotates about its C of G once it's released. Think of winding up and releasing a discus. (But you can't ignore wind resistance in a looping windsurfer, they won't rotate around the exact C of G )

"In case of non planing the sail force acting at the COE before the cg let the board going downward, the moment is left turning. Is the COE behind the cg the board is going upwind, the moment is right turning. "

Did you understand his words above,what he want to say??

If you've ever steered a yacht with a jib, and then without you'll get a "feel" for what he's saying. He's applying the concept on starboard tack.
changing foot pressure between back and mast foot is how you'll feel it windsurfing/foiling

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fpw9082 said..

Subsonic said..

fpw9082 said..

Ian K said..

fpw9082 said..
Dietrcih text:
"every body rotates about the center of gravity, not the COR. The COR is nonsense. The forces relative to the center of gravity produce a moment which forces the body to rotate. Are the moments balanced the board goes straight.In case of non planing the sail force acting at the COE before the cg let the board going downward, the moment is left turning. Is the COE behind the cg the board is going upwind, the moment is right turning. "

Can some one explain his words,that board will rotate about center of gravity???
For me COE in relation to c.g. has nothing to do with board turning.

A body rotates around its C of G when all external forces are removed. But to get it to rotate in the first place you need to apply external forces. It generally only rotates about its C of G once it's released. Think of winding up and releasing a discus. (But you can't ignore wind resistance in a looping windsurfer, they won't rotate around the exact C of G )

"In case of non planing the sail force acting at the COE before the cg let the board going downward, the moment is left turning. Is the COE behind the cg the board is going upwind, the moment is right turning. "

Did you understand his words above,what he want to say??

If you've ever steered a yacht with a jib, and then without you'll get a "feel" for what he's saying. He's applying the concept on starboard tack.
changing foot pressure between back and mast foot is how you'll feel it windsurfing/foiling

When young kids learn how to steer 470klass,they remove rudder and learn how to steer with jib and main sail.Doing this they change relation between COE and CLR,nothing to do with c.g.




here is top view for 2.0m sail when foiling

CG and COE of the rig not the whole kit and caboodle.

fpw9082 imagine getting towed by a boat (wake foiling) and you are on your windfoil board. To balance things your weight will be over the center of the board in a surf stance. Now imagine this same situation and you quickly jump into your windsurfing stance. With your front foot way over to one side of the board it would immediately turn hard! This is the force that counters the sail side force. Our weight being off center always imparts a turning moment into the wind. The 2D sailing balance analogy doesn't fully apply due the differences in the geometry of boats verses windsurfing.

I have come to believe that there is constant slight angulation of the board (<5 deg) for for all points of sail above broad reach, effectively "angleing" the front wing resulting in either a) moving the lateral resistance forward as the wing angulation creates increased exposure of the wing to lateral forces or b) the lift generated from the wing when angled creates opposition the CoE in the sail. I am leaning towards b.

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gorgesailor said..

fpw9082 said..

WhiteofHeart said..
Yeah it always made me wonder aswell, especially once you start riding 3.0's and 2.5's and the clew doesnt even reach the mast hahahah. I asked the same question to a friend of mine who's a nautical designer of racing yaghts. He said he didnt know, but it had to be balanced otherwise it doesnt work.

It is funny thing that even windsurfing desingers dont have explain..(but this is first thing you have learn in wsurf-school,"board go in straight line only if COE and CLR is in same line")
It seems in windsurifng nobody knows anything but evertyhing works in practice.This is miracle.
Our sport evolution is based on trial and error method..:) :)

(i have my half-explain,when board is heel to windward than front wing handled lots side force,so CLR is just in front of back feet,,BUT there is lots of situation where board is flat and still going in stragiht line so this is still unclear...)

None of the diagrams have legs... Seriously... This is what you are missing & what Dietrich Hanke & White of Heart were saying. Think of the kite example. As much as we might not like it we are more like Kite foilers than Sailboats.

Just imagine you could take a Windfoiler in perfect trim & remove the pilot. Just fix the mast & boom position, & for a second imagine the sailor weight is not affecting the longitudinal trim. Without the forces being directed through the sailors legs will the craft still go straight? NO the sailor is balancing the forces & moments though his legs.

Like snowboarding; gravity is the COE of the sail, your boards rail is the foil. Depending on how you adjust your weight over the front / backleg you can change your direction from completely downhill to almost perpendicular to the mountainside. Backleg preassure is uphill / upwind, frontleg preassure is downhill / downwind. The steering works because you load for example the frontfoot, making the front of the board heavier than the back and steering it downhill, and vice versa for uphill. You need to balance the two to not end up going straight down the mountain, or end up pointing too high up the mountain and loosing speed. Same goes for windsurfing.

Ofcourse the sail (and foil) is a little different from gravity in that it doesnt only generate a force sideways but a little bit more forward than sideways, bluntly meaning for windsurfing, to put it in the snowboarding example, our "gravity" doesnt come from right below but a little bit angled relative to the slope so we can go "uphill".

In practice, for windsurfing by moving your hands forward on the boom, changing the position of your harnesslines, or changing the position of your hips slightly, you can push the sails power more through for example the backleg, making the backleg "heavier" and thus pushing the back of the board downwind / front of the board upwind. The opposite should hold for steering downwind, although personally I think in practice I lift my frontfoot, changing the boards angle and thus moving my rotational axis back from the frontwing more towards the mast. (Because less angle would mean the front wing provides less of the counter-drift force and the mast provides relatively more, movin the sum back)

In the end for going upwind I suppose its a balance game like the snowboard example, if you have too much power on either leg you're suboptimal. In all honesty I feel this on the water aswell, for me having both legs straight is the fastest way of going upwind, but to manage that my footstraps, mastbase and most importantly harnesslines have to be in the right place. You often see people who are sailing with a bent frontleg upwind have their sail tilted farther back, and people who have 2 straight legs have their sail more upright/forward. Logical if you follow my reasoning, since bending the frontleg means you have more weight / power on the front of the board and have to compensate by angling the sail back. In the end the balance is delicate, since your weightdistribution determines both your angle and your height, I suppose thats why its so hard (and important) to get the trim exactly right.

The fact that you're not on the centerline is indeed of importance, but I'm gonna have to keep breaking my head on that for the moment. Keep in mind that upwind on a wide board, the biggest part of your weight is not on your feet but in the harness, especially if you look at the angle of the rider and board relative to the water, I think only a small portion of your weight is pushing the windward side of your board down (Y-Axis). I think most of it is more of a combination of the sail lifting your weight, being at an angle, and since its fixed at the mastfoot, part of your weight ends up pushing the board through the X-axis through your legs to counter being pulled over the board (Which basically returns us to the snowboarding example), and part of it goes down through the mastfoot because of physics which I find hard to explain, other than to refer people to armwrestling in reverse (try lifting someones hand with your arm at a 45 degree angle), and the fact that your elbow (mastfoot) takes the load.

Just imagine foil as airplane under water,with one exception, windsurifng system has c.g. on side ,airplane has on centerline.
c.g. is above front wing (and slightly in front,to ensure longitudinal "pitch" static stability.)
If foil has flat front and rear wings and board is flat,than CLR is between mast and vertical stabilizer,closer to the mast because mast has larger area.Then " compensating/stabilizing" moment arm is from CLR to c.g.
(but here we also have a case that leads people to wrong conclusions,about it next time..)

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fpw9082 said..

Ian K said..

Ian k how can you explain why Dietrich put Thrust force at board level,not at sail COE ,2m above board?
If he put it on sail COE ,than tail wing will must produce so much bigger force to balance pitching moment...

mauiultrafins.com/technology-2/hydrofoil-mechanics/

No, can't see why he'd do that. He seems to be attempting to resolve moments about a point on the deck directly below the CG. He's also got the CG directly over the centre of lift of the foil which isn't necessarily the case. He's not good with words, he's even worse with diagrams.

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fpw9082 said..

Ian K said..

Ian k how can you explain why Dietrich put Thrust force at board level,not at sail COE ,2m above board?
If he put it on sail COE ,than tail wing will must produce so much bigger force to balance pitching moment...

mauiultrafins.com/technology-2/hydrofoil-mechanics/

all he's representing are the forces acting on the foil Nothing more.

As I said before ,how vertical surfaces on foil affect yaw stability:

link:
www.mackiteboarding.com/news/hydrofoiling-can-you-change-your-rear-wing/

quote from text:
"The addition of a rear wing with more winglet surface will increase yaw (twist) stability without effect on its pitch or roll. This can be good for having a "locked in" feeling at higher speeds or in powerful turns but may seem too "tracky" for loose riding styles.
The Speedster features large winglets on both of its wings, which act like quad fins on a surfboard. At moderate speeds it gives a locked-in, confident feeling that beginners will appreciate. However, as speeds progress it gets to be a little tracky for my taste. "



This is reason why all freeride foils version have bigger vertical areas at wingtips or add one vertical stabilizer (like Neilpryde ALU has)
than high performance foils.That gives easier ride for bigginers ,foil is not so sensitve to yaw but at higer speed become to "tracky"..

freeride




high performance



code "46=46=dne"

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lakeeffect said..

Aren't the forces in the sail transmitted into the board at the sail mast foot and at your feet? Hanke calls it Thrust. Drake calls it Drive. All this is in the longitudinal direction. In the lateral direction Hanke call it a side force. Drake calls it heel force. Both Thrust/Drive and Side/Heel forces generated by the sail are transmitted into the board by the mast foot and your feet.

Mast foot pressure is not necessarily horizontal.

But the original post was not considering internal forces. You have to first define your system and then look at the external forces and their associated moments on that system. FPW was clearly considering the board, rider, foils and rig as the system. The external forces acting on that system are then wind, water and gravity.

You don't have to worry about the internal forces unless for instance you wanted to know what size bolts were needed to hold the foil in the box. Start a new thread for that one.

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lakeeffect said..

Aren't the forces in the sail transmitted into the board at the sail mast foot and at your feet?

You are right,every external force can be replace with their internal forces,external forces sail force and gravity can be replace with internal horizontal/vertical forces at feet and mast foot.(But Hanke didnt do it,I also wonder why he didnt!)

But in windsurfing system , internal " arrangement" (relations between sailor-lines-boom height etc) will determine magnitude of sail force(external force) so to find equilibrium you must balance the torques around it for both: the sail and the board.