Where is CLR on foil?

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gorgesailor said..

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/

Isn't this because thrust from sail is primarily transferred through legs/feet to board??

Im in this camp. The CLR or COE locations dont matter as much, for through your body you can moderate the forces. It doesnt matter where the center of the sails force is located, for that has little to do with how that force is transferred to the board. We differ from sailboats because our mast is not fixed, and thats why the same principles dont hold.

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fpw9082 said..

WhiteofHeart said..

gorgesailor said..

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/

Isn't this because thrust from sail is primarily transferred through legs/feet to board??

Im in this camp. The CLR or COE locations dont matter as much, for through your body you can moderate the forces. It doesnt matter where the center of the sails force is located, for that has little to do with how that force is transferred to the board. We differ from sailboats because our mast is not fixed, and thats why the same principles dont hold.

Your explanation is similar as Hanke, especially this part with sailboat and windsurf comparison,did you contact him?

I didn't & doubt WOH did either... This is, IMO a result of using science to explain ones experience rather than trying to fit ones (limited)experience to some theoretical scientific model. This is why the most successful Windsurfing designers are Windsurfer/Windfoilers first & Designer/Engineers second.

Thanks for the thread. There are many useful informations. I belong to those that find that understanding the basic physics behind the practice help:
- improve practice and correct "bugs",
- choose suitable hardware,
- tune the hardware.

I'm "half beginner" and fighting to improve my balance upwind in light wind. This thread helps me go out of the CLR aligned with COE paradigm.

I like the idea from Hanke that once foiling/flying, direction is primarily imposed by the board/foil roll (like a plane). Sail and body are the motor.

There is a complex transmission of sail power to the board through body/feets and mast foot have not found yet studies/analysis on that specific aspect)

COE may not be aligned with "fin", like is usually the case on a planning board, which will be compensated by the pilot with its feets and board width to roll the board.

In my balance upwind in light wind, I have to combine this with:
- low powered rig weight balance,
- rig CoG compared to sailor position,
- rig that needs to be hold "still" by the sailor,
- longitudinal position imposed by foil stability
...

The question behind is:
- does upwind in lightwind with "big sails" requires a dedicated tuning ?
- how to make it "comfortable"
- does board width help (at front froot, at back foot).

But this is another topic

JMF

Also, as soon as there is any heel on the board then the CLR is not at the CoP of the mast. Windward heel will pull it forward towards the front wing somewhat. How much depends on the ratio of Side force do vertical force required and efficiencies of the mast vs wing and how negative the stabaliser is but most importantly the AoA of the foil. So even a small amount of windward heel will create a yaw moment and a move in virtual CoLR. There is only one thing which is for sure and that is that the forces are ballanced.

Quite a long topic, seen in many places. Mechanics laws on a macro level are well known for centuries and the issue when a system is mysterious is always that the subject isn't well defined.
Most of the problem comes from the fact that we try to apply the mechanics described more than centuries ago for large sail boat to a windsurf. And a windsurf isn't a sail boat because the mast is mounted on a universal joint. If you try to do this, you need to have a sail perfecly 'locked' by the rider. It is suitable to describe a situation where every force is steady, and anybody sailing knows that water, wind (direction and force) are anything but steady.
So the only solution is to consider 3 separeted 'solid' system (but in fact it is just simplification) : the rider, the sail and the board.
Then you consider what are the forces applied.
Considering the board from a top view, and ignoring hull effects (wich is close to reality in the case of a foiled gear), you have the side effect of a fin (foil mast) wich is directed windward (with a drag compoment), the presure applied by the rider with his feet, usually simplified to one force betwen the two feet, and directed leeward with a compoment forward (as the position of the straps obviously reveals), and the force from the mast (I purposively don't say sail) wich is WINDWARD. Yes, I says again : your mast is pushing your board upwind. Easy to prove : last time your mastfoot link failed, in which direction did your mastfoot go ?

Then consider the sail : three forces. The lift generated by its advance throught the air. Pushing downwind and forward, the rider pulling on the wishbone, and the board (via the mastfoot) pushing downwind (in fact it is the same but opposite of the one that the sail apply to the board). and from above the rider force is precisely between the push of the wind and the one from the board...


Now back to windfoil, you must consider the effects of inclining the board windward, so the lift of the front wing has a side compoment, and this modifies the balance. Very tricky to make equation out of this, but when you lean you foilboard, you're modifying the yaw balance...

Ellway did a good series of posts which clearly explain some of the foiling forces. worth a read