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Where to shim?

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Peter_Frank
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Re: Where to shim?

Postby Peter_Frank » Tue Nov 05, 2019 9:41 pm

It has quite a lot of impact.

If you shim just 2 degrees, the balancing point will move 3.5 cm (1.4 inch) rearwards, meaning you can stand 7 cm (almost 3 inches) further rear with your front foot, and be in balance.

Meaning, less front foot pressure if you dont move your feet/straps :thumb:

8) Peter

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Re: Where to shim?

Postby Horst Sergio » Tue Nov 05, 2019 9:45 pm

Yes, my a) and b) would make the nose point more downwards then before and b) would additionally bring your foot stance together with your board more forward.

If we suppose that you just need a stance more forward, then you have still many options, especially now as we know what board and foil you have:
matanshapira wrote:
Tue Nov 05, 2019 9:01 pm
I have LF Impulse(1100sqm) with Kanaha Shapes 37" (no tracks)
I) easiest option as said your "3."
II) Peter Franks double shim at both ends of the strut (wood shim under the strut head plate and one aluminium shim beteween fuselage and strut or cutting the strut at an angle)
III) New holes in the board
IV) The more basic a foil is, the easier it is to modify, so good luck it is a liquid force :thumb: :
New holes in the (alu?) fuselage, to bring the strut conection closer to the front wing ... would be my favorit as much easier and stable, than II and III.

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Re: Where to shim?

Postby matanshapira » Tue Nov 05, 2019 9:56 pm

Horst Sergio wrote:
Tue Nov 05, 2019 9:45 pm
Yes, my a) and b) would make the nose point more downwards then before and b) would additionally bring your foot stance together with your board more forward.

If we suppose that you just need a stance more forward, then you have still many options, especially now as we know what board and foil you have:
matanshapira wrote:
Tue Nov 05, 2019 9:01 pm
I have LF Impulse(1100sqm) with Kanaha Shapes 37" (no tracks)
I) easiest option as said your "3."
II) Peter Franks double shim at both ends of the strut (wood shim under the strut head plate and one aluminium shim beteween fuselage and strut or cutting the strut at an angle)
III) New holes in the board
IV) The more basic a foil is, the easier it is to modify, so good luck it is a liquid force :thumb: :
New holes in the (alu?) fuselage, to bring the strut conection closer to the front wing ... would be my favorit as much easier and stable, than II and III.
I - I'll go for it next session
II - I doubt the fuse->struct connection can be shimmed as the screw and the screw head won't fit well into the fuselage when coming at an angle.
III - no more room at the end of this tiny board
IV - carbon fuselage, but Stringy makes Aluminium fuselage with such offset for LF too. The downside, it'll probably weigh more than my LF carbon fuse(500gr if I'm not mistaken)

Sounds like it's either I or IV.

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Re: Where to shim?

Postby grigorib » Tue Nov 05, 2019 10:13 pm

Peter_Frank wrote:
Tue Nov 05, 2019 8:18 pm
grigorib wrote:
Tue Nov 05, 2019 6:13 pm
matanshapira wrote:
Tue Nov 05, 2019 11:45 am
Where should I shim if I want to reduce front foot pressure without changing the stability of the foil?

1. Fuselage to mast connection
2. Mast to board connection
3. Rear wing to fuselage connection (stating it just for the record as it will affect stability)
I don't think it''s possible to shim without affecting stability.

No #1 and #2 make no sense nor difference
Go for #3 pointing stabilizer few degrees up and that will have the effect. That will reduce stability but way less compared to improved stance.

It IS possible, #1 and 2 has been proven, in earlier threads and videos.

I made a scetch showing why it works, and without altering stability as the wing aoa's are not altered :thumb:

8) Peter
ShimPrinciple.jpg
Makes sense
So #1 and #2 need to be made at the same time.
Last edited by grigorib on Tue Nov 05, 2019 10:16 pm, edited 1 time in total.

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Re: Where to shim?

Postby Horst Sergio » Tue Nov 05, 2019 10:16 pm

matanshapira wrote:
Tue Nov 05, 2019 9:56 pm
II - I doubt the fuse->struct connection can be shimmed as the screw and the screw head won't fit well into the fuselage when coming at an angle.
Don't worry, if you just shim 2° as I did here, there is enough play and not to much pain for the screws.
On a 10 cm wide strut these are about 4 mm in shim height difference and so on a 100 cm strut around 4 cm of moved pressure point. But I did it to mostly to get the nose of my inflateable board more up and the foot stance for the mono more back at the same time for more compfortable higher board speeds.

It is the same just opposite direction as described by George, just with an alu foil and used a cutted strut part as shim instead of a less defined piece of plastic.
cutting-shim.jpg
shimed-fuselage-strut.jpg
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Re: Where to shim?

Postby flying grandpa » Wed Nov 06, 2019 12:15 am

I simply shim in:
4. Front wing - fuselage connection.
This reduces front pressure, improves pitch agility a bit, reduces max speed a bit. Usually there is no need for other adjustments (1; 2 or 3)

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Re: Where to shim?

Postby Kamikuza » Wed Nov 06, 2019 1:43 am

Don't say whether or not you've got a board with a box or rails....

To reduce front foot pressure without messing with the trim of the foil, move the mast back relative to your stance. So either move the mast back in the rails or your foot position forward. If you're using straps with a box, you might have very limited options.

Otherwise, you'll have to put a shim under the rear wing but it shouldn't affect the stability ... whatever you mean by that.

Or maybe your fuselage is bent?

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Re: Where to shim?

Postby matanshapira » Wed Nov 06, 2019 6:26 am

flying grandpa wrote:
Wed Nov 06, 2019 12:15 am
I simply shim in:
4. Front wing - fuselage connection.
This reduces front pressure, improves pitch agility a bit, reduces max speed a bit. Usually there is no need for other adjustments (1; 2 or 3)

You mean you put a shim under the front screw of your front wing? This makes the lift go a bit towards the back, right? Wouldn't it increase the drag?

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Re: Where to shim?

Postby matanshapira » Wed Nov 06, 2019 6:33 am

Kamikuza wrote:
Wed Nov 06, 2019 1:43 am
Don't say whether or not you've got a board with a box or rails....

To reduce front foot pressure without messing with the trim of the foil, move the mast back relative to your stance. So either move the mast back in the rails or your foot position forward. If you're using straps with a box, you might have very limited options.

Otherwise, you'll have to put a shim under the rear wing but it shouldn't affect the stability ... whatever you mean by that.

Or maybe your fuselage is bent?
Sorry, only inserts.
Fuselage might be the issue, will check. Those carbon fuselages from LF are not accurate at all and I already noticed that there's a twist when I bought it but they said it's within the acceptable range.

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Re: Where to shim?

Postby Kamikuza » Wed Nov 06, 2019 7:21 am

Inserts = rails or holes through board? Strapped I assume too? Try a session strapless and see if moving the relative CoG is the issue.

And some foils really push the front foot until you're in their cruising speed range... Try going faster :lol:

No twist is acceptable :o


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