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Foil Shims, how to use?

 
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allenlight

Since 19 Jul 2008
37 Posts

 



PostThu Aug 19, 21 6:54 pm    Foil Shims, how to use? Reply with quote

Been having fun with various foils this summer. One of the foils I have is a 'Liquid Force Happy Foil' (Medium Aspect) came with shims for the front and back wings. I've only had a couple of sessions on this front and back wings and without shims. It was fine (much faster than my Impulse), and like most new setups it takes me a while to get the feel for it.

Question; how do I use the shims? There is one shim for the front and three for the rear. It looks like the change the angle of attack on the wings, but I'm not sure what does what.

Any insight would be appreciated!

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eric

Since 13 Jan 2006
1700 Posts

XTreme Poster



PostThu Aug 19, 21 7:38 pm     Reply with quote

https://youtu.be/mVdSx5eNdUA

Great shim video

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ldhr

Since 21 Jul 2009
1393 Posts
Hood River
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PostFri Aug 20, 21 10:45 am     Reply with quote

Modern foils..... if they are well designed don't need shimming.
Shimming is a holdover of the early poorly designed foils.
In other words - you shouldn't need to shim a good foil.
If the foil is working well for you - don't mess with it.
If the foil has too much lift or too little - read further.


If you shim rear wing to point the front edge down - you get more lift, this also moves the center of lift forward and increases drag.

If you shim the rear wing to point the front edge up - you get less lift, moving the center of lift back and reducing drag.

When you put more downforce on the rear wing you end up moving the foil back to compensate for the increased lift and more forward center of effort. Even if you don’t move the foil in a mount your foot placement and center of effort will adjust forward in relation to the foil. By moving the whole foil back it will tend to track more and be harder to turn.

You put less downforce on the rear wing, lift decreases, center of effort moves back, foil moves forward in relation to the rider, more responsive and twitchy turning.

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Kmun

Since 05 Jul 2009
224 Posts

Stoked



PostFri Aug 20, 21 11:29 am    Mast adjustment relative to stance position Reply with quote

ldhr wrote:
Modern foils..... if they are well designed don't need shimming.
Shimming is a holdover of the early poorly designed foils.
In other words - you shouldn't need to shim a good foil.
If the foil is working well for you - don't mess with it.
If the foil has too much lift or too little - read further.


If you shim rear wing to point the front edge down - you get more lift, this also moves the center of lift forward and increases drag.

If you shim the rear wing to point the front edge up - you get less lift, moving the center of lift back and reducing drag.

When you put more downforce on the rear wing you end up moving the foil back to compensate for the increased lift and more forward center of effort. Even if you don’t move the foil in a mount your foot placement and center of effort will adjust forward in relation to the foil. By moving the whole foil back it will tend to track more and be harder to turn.

You put less down-force on the rear wing, lift decreases, center of effort moves back, foil moves forward in relation to the rider, more responsive and twitchy turning.


Some mast tracks have limited adjustment range or are of old school setting compared to the board’s deceptive foot traction pad placement.

1. Instead of moving the mast track can one simply adjust their stance/foot position?

2. Is it true that your directions, for example; of moving the mast placement back on the board could be replicated by moving the foot position forward?

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Pepi

Since 16 Jun 2006
1809 Posts
Pure Stoke Sports
Shop Owner

CGKA Member


PostFri Aug 20, 21 11:59 am     Reply with quote

I don't want to fully contradict Laird's post, but......
There are times when a shim is helpful (windfoilers rely heavily on them for tuning their foils, but they have little adjustment range).
Foilboards from different brands still have some slight variations in track placements (some forward, some back) and if your track does not move far enough in the direction needed, a foil shim on the stabilizer can be helpful.

Same goes with getting the board to 'pop' up on a foil. In lighter wind conditions, i actually like to shim my back stabilizer to create more lift. I have also used the same shim to allow me to make tighter radius carving turns on swell.

For the LF foils, I did the same as above. It did cause a bit of front foot pressure, but it allowed my stock foils to have a much tighter turning radius and a bit more POP when jumping.

These adjustments are not for everybody so if you are going to shim, do it wisely and do it with a purpose in mind.

ldhr wrote:
Modern foils..... if they are well designed don't need shimming.
Shimming is a holdover of the early poorly designed foils.
In other words - you shouldn't need to shim a good foil.
If the foil is working well for you - don't mess with it.
If the foil has too much lift or too little - read further.


If you shim rear wing to point the front edge down - you get more lift, this also moves the center of lift forward and increases drag.

If you shim the rear wing to point the front edge up - you get less lift, moving the center of lift back and reducing drag.

When you put more downforce on the rear wing you end up moving the foil back to compensate for the increased lift and more forward center of effort. Even if you don’t move the foil in a mount your foot placement and center of effort will adjust forward in relation to the foil. By moving the whole foil back it will tend to track more and be harder to turn.

You put less downforce on the rear wing, lift decreases, center of effort moves back, foil moves forward in relation to the rider, more responsive and twitchy turning.

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Hood River, OR
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allenlight

Since 19 Jul 2008
37 Posts

 



PostFri Aug 20, 21 8:51 pm     Reply with quote

I appreciate all the feedback on this, and now have and idea about what to expect from some experimentation.

It sounds like shimming the rear wing with an increased angle of attack will have some similar effects that I experienced when I moved the stabilizer forward on the fuselage (there are two placements for the stabilizer about 1/2" apart). The closer placement resulted in tighter turns but a more 'twitchy' feel. Further back created a more stable feel but slower turning.

The difference (if I'm understanding the feedback), is that the rear shim will give the foil some faster lift (requiring more front foot pressure to compensate) at the expense of some additional drag.

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