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shimming the foil question - moses

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cwood
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Re: shimming the foil question - moses

Postby cwood » Tue Mar 10, 2020 11:36 am

if you can avoid it, don't shim the stabilizer. By doing so you are fighting the neutral trim of the setup. It will introduce turbulence. You are far better to move straps or move mast to gain the desired center of gravity that maintains the trim of the neutral setup. Now, of course this is not always possible.

The next thing is shimming the mast to fuse connection, which is easy to do on Moses. A small chunk or credit card or any thin plastic and a thin strip of gorilla tape in the fuse behind the rear mast screw will cant the mast forward at neutral flight and therefor move your CG forward and give you more forward push down on the wing for a given stance. Need more?, add a second layer.

Be careful when you put the screws in....get them started with the fuse perfectly parallel to the mast foot bottom, then as you snug them home you will see the slight angle. Also, do not over tighten the screws as the bottoms of the thread barrels are not opposed by the bottom of the fuse trough. Just nicely tight.
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Re: shimming the foil question - moses

Postby merl » Tue Mar 10, 2020 4:24 pm

The assumption here, and in some earlier discussions, is that there is a "neutral trim" that is somehow "just right", and if you shim the stab then you are somehow making things worse. Is there any real truth in this? Have the designers not just adjusted the angles for a certain amount of lift, but the amount is a bit arbitrary and therefore can be tweaked (at least within small margins)?

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Re: shimming the foil question - moses

Postby kitexpert » Tue Mar 10, 2020 8:36 pm

cwood wrote:
Tue Mar 10, 2020 11:36 am
if you can avoid it, don't shim the stabilizer. By doing so you are fighting the neutral trim of the setup. It will introduce turbulence. You are far better to move straps or move mast to gain the desired center of gravity that maintains the trim of the neutral setup. Now, of course this is not always possible.

The next thing is shimming the mast to fuse connection, which is easy to do on Moses. A small chunk or credit card or any thin plastic and a thin strip of gorilla tape in the fuse behind the rear mast screw will cant the mast forward at neutral flight and therefor move your CG forward and give you more forward push down on the wing for a given stance. Need more?, add a second layer.
Wrong. Shimming mast to fuse connection is in vain because it tilts the whole lifting system. When riding you adjust all the time AoA of the foil by weight shifts and then you automatically cancel possible small change in fuse angle. If gross adjustments is done you'll counter it with board position: if fuse points down your board will end up riding nose up.

Moving feet positions or straps of course have a big influence because it changes weight distribution in relation to front wing, where lift occurs. Moving foil front or back moves your position respectively on board. For example if you feel you must put your front foot too far front by all means then move foil attachment backwards.

Real adjustment is done between the wings, front wing and stabilizer. You can adjust either of them or both, but usually stabilizer because it is smaller and easier to adjust. If foil shoots up there is too little stabilizing effect (too small stabi, too short fuse or wrong AoA for stabi). AoA can be changed by shimming. Hf is quite a lot like an aeroplane, they both have some built-in AoA (difference) for wing and (horisontal) stabilizer. In planes it is also partially mechanically adjustable (elevator), in foils you have some basic preset and then you use weight shifts to determine the level of "flight". Stabilizer balances front wing lift and resists rapid changes in flying height, but if you have very good balancing skills you can even use hf without stabilizer.

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Re: shimming the foil question - moses

Postby cwood » Tue Mar 10, 2020 8:42 pm

kitexpert wrote:
Tue Mar 10, 2020 8:36 pm
cwood wrote:
Tue Mar 10, 2020 11:36 am
if you can avoid it, don't shim the stabilizer. By doing so you are fighting the neutral trim of the setup. It will introduce turbulence. You are far better to move straps or move mast to gain the desired center of gravity that maintains the trim of the neutral setup. Now, of course this is not always possible.

The next thing is shimming the mast to fuse connection, which is easy to do on Moses. A small chunk or credit card or any thin plastic and a thin strip of gorilla tape in the fuse behind the rear mast screw will cant the mast forward at neutral flight and therefor move your CG forward and give you more forward push down on the wing for a given stance. Need more?, add a second layer.
Wrong. Shimming mast to fuse connection is in vain because it tilts the whole lifting system. When riding you adjust all the time AoA of the foil by weight shifts and then you automatically cancel possible small change in fuse angle. If gross adjustments is done you'll counter it with board position: if fuse points down your board will end up riding nose up.

Moving feet positions or straps of course have a big influence because it changes weight distribution in relation to front wing, where lift occurs. Moving foil front or back moves your position respectively on board. For example if you feel you must put your front foot too far front by all means then move foil attachment backwards.

Real adjustment is done between the wings, front wing and stabilizer. You can adjust either of them or both, but usually stabilizer because it is smaller and easier to adjust. If foil shoots up there is too little stabilizing effect (too small stabi, too short fuse or wrong AoA for stabi). AoA can be changed by shimming. Hf is quite a lot like an aeroplane, they both have some built-in AoA (difference) for wing and (horisontal) stabilizer. In planes it is also partially mechanically adjustable (elevator), in foils you have some basic preset and then you use weight shifts to determine the level of "flight". Stabilizer balances front wing lift and resists rapid changes in flying height, but if you have very good balancing skills you can even use hf without stabilizer.
I guess we will agree to disagree. Even in aircraft, if you apply elevator or trim to correct flight due to CG being out of whack, you will constantly fight it. No different in a hydrofoil.


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Re: shimming the foil question - moses

Postby kitexpert » Tue Mar 10, 2020 9:20 pm

With hf you change CoG by your stance location and weight distribution between your feet, in planes it is quite fixed.

Tilting fuse to mast or tilting mast to board is silly. When board flies level or slightly nose up it is ok for these, it should be a factory setting and I see no reason why it wouldn't be.

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Re: shimming the foil question - moses

Postby Kamikuza » Tue Mar 10, 2020 10:09 pm

kitexpert wrote:
Tue Mar 10, 2020 9:20 pm
With hf you change CoG by your stance location and weight distribution between your feet, in planes it is quite fixed.

Tilting fuse to mast or tilting mast to board is silly. When board flies level or slightly nose up it is ok for these, it should be a factory setting and I see no reason why it wouldn't be.
One is a hydrodynamic solution, the other mechanical. Both will change how much “pressure” you’ll feel on your feet ... if your feet are in the same position before and after.

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Re: shimming the foil question - moses

Postby purdyd » Tue Mar 10, 2020 10:10 pm

I’m battling through with shims on the stab.

From what I understand and I saw a nice video on it where Adrian roper from axis foils explained it the greater the difference in the angle between the front wing and stabilizer, the steadier it is, and the more front foot pressure you will need.

I just got a new foil setup with a very small and neutral stabilizer and it has incredible glide but it is indeed fussy in higher winds and I would like a bit more front foot pressure.

The problem is there is a place where I want to be on my small board to get it to pop up and that is different from where I want to stand when I ride.

And also, it is easy to loose lift as you are flying fairly neutral and if you get a little nose down and came come down quick.

Both setups I have comes with shims for the rear wing and you can tune your setup.

So I am of the opinion there is not really one angle for the stabilizer and it is the easiest to tune. But you will likely have to move the foil in the tracks or adjust your stance if you change the angle.

Also shimming the stabilizer is quick and easy so give it a try.

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Re: shimming the foil question - moses

Postby TomW » Tue Mar 10, 2020 11:52 pm

Moses wings are set up perfectly if you use wing and stab recommendation they have. That's what you pay for, everything is set up right out of the box. If you are using footstraps and feel unbalanced, your footstraps are in the wrong position. Period.
If you are using 633 or big wing, take off your footstraps.

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Re: shimming the foil question - moses

Postby Kamikuza » Wed Mar 11, 2020 7:08 am

TomW wrote:
Tue Mar 10, 2020 11:52 pm
footstraps
Wull, thar's yer problem!

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Re: shimming the foil question - moses

Postby Frankieboy » Wed Mar 11, 2020 8:09 am

Hi guys thanks for the input.

I ride strapless and moved the mast all the way back. My back foot is in front of the mast.
I ride a 120x45 board now but will switch to KS 94cm pocket board, that is the problem.
When using the 330 stab the balance and feet position is fine (more at ,the back).


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