Forums > Kitesurfing Foiling

Stable vs unstable foils - Front wing shape?

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Created by Lambie 4 months ago, 4 Jun 2018
Lambie
VIC, 698 posts
4 Jun 2018 7:06PM
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What makes a foil more or less stable in the roll plane - ie easier to turn but less stable and visa versa (harder to turn but more stable) ?

Some front wings have really funky curves with most having down turned windtips while some like the Zeeko Carver are almost flat from wing tip to wing tip ??

If I want something looser (or more stable on the other side of the question) is the shape of the front wing going to give me a clue ? Im very new to this foiling thing but can now ride in both directions but am interested in what front wings and their shape (not so much the low or high aspect stuff) does for manourvability ??

Plummet
4231 posts
4 Jun 2018 6:20PM
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More or vertical stabilizer, longer fuse, more stabalizer size comparable to front wing, increased wing size, inc stabilizer aoa.

All these things increase stability with the disadvantage of decreased manuveuribility.

Easiest way to improve stability with your current set up is to shim the rear stab to increase aoa.

warwickl
NSW, 1019 posts
4 Jun 2018 8:42PM
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Select to expand quote
Plummet said..
More or vertical stabilizer, longer fuse, more stabalizer size comparable to front wing, increased wing size, inc stabilizer aoa.

All these things increase stability with the disadvantage of decreased manuveuribility.

Easiest way to improve stability with your current set up is to shim the rear stab to increase aoa.


100% agree and doing this to my Zeeko Carver wing has worked for me.

Kamikuza
QLD, 3441 posts
4 Jun 2018 11:47PM
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No idea for sure but from what I've noticed though is that wider and flatter makes rolling more work.

The LF FF and the Double Agent rolled ok. Call it the base line...
The Hoverglide really didn't want to without lots of body English.
Oddly enough the Alpine Access which had a similarly wide, high AR wing rolled maybe a little more freely than the LF and DA.
Spitfire was way too twitchy for me but I didn't have long enough on it, apparently.
Axis kite foil wing is flat but rolled freely too. The prototype 720cm wide surf wing with clipped tips rolled faster than the 720 but wasn't as nice to ride for me, although others loved it. The 920 was too stable for kiting IMO.

I think there are many paths to foiling nirvana, you just gotta chose the one that suits. Which is why we have 10,000 kite brands probably :D

For me, low span, low AR, high chord wings seem to have more issues with speed than do higher AR wings with a "nice" anhedral... Your guess is as good as mine!


Select to expand quote
Plummet said..
More or vertical stabilizer, longer fuse, more stabalizer size comparable to front wing, increased wing size, inc stabilizer aoa.

All these things increase stability with the disadvantage of decreased manuveuribility.

Easiest way to improve stability with your current set up is to shim the rear stab to increase aoa.

He's talking specifically about roll stability.

bigtone667
NSW, 955 posts
5 Jun 2018 8:10AM
Thumbs Up

My experience is:

The larger the front wing, the more stable you become (but quite a few people will say it is more boring as well) and generally the harder it is to turn at speed. But your turning at low speeds is super fast and super steady (pivot turn). But, the larger the wing the slower you are overall.

Original Zeeko Blue/White had a 3cm (maybe 4cm) rear fin and they reduced the size to about 2cm. It gave the Blue/White some serious yaw "fun".....

If I use the Zeeko Spitfire as an example..... the original wing set was (for me) much challenging. I needed good speed and had to be quite precise in my movements. The XLW wing set required less speed and was more forgiving in turns if I was not quite correctly balanced.

My advice is to figure out where you think you will ride a foil and on what occasions, and then make a decision on the type.

For example:

If it is a lake, then I am generally interested only in riding the foil in low wind conditions (8-15 knots) and I do not want to use a foil kite. So my selection was based on being able to get up and running early (I picked a wide board for the foil) and I picked a largish wing (700cm2 plus).

If I am in the surf/swell, then I am interested in riding the foil in 10-25 knots with an LEI. So So my selection was based on being able to get up and running early, I need a board with some nose rocker and foil that is not too fast in a wave (so I picked a huge wing).

It's fun figuring out what you want.

RAL INN
VIC, 2559 posts
5 Jun 2018 8:58AM
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Lambie, I have a feeling that you are now going through one of the learning phases and maybe are in the process of finding out what brain input goes into roll balance.
something that muscle memory will take over for you.
For now maybe work on keeping more than 50% of mast in water to just help that bit.

Plummet
4231 posts
5 Jun 2018 8:43AM
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Kamikuza said..
No idea for sure but from what I've noticed though is that wider and flatter makes rolling more work.

The LF FF and the Double Agent rolled ok. Call it the base line...
The Hoverglide really didn't want to without lots of body English.
Oddly enough the Alpine Access which had a similarly wide, high AR wing rolled maybe a little more freely than the LF and DA.
Spitfire was way too twitchy for me but I didn't have long enough on it, apparently.
Axis kite foil wing is flat but rolled freely too. The prototype 720cm wide surf wing with clipped tips rolled faster than the 720 but wasn't as nice to ride for me, although others loved it. The 920 was too stable for kiting IMO.

I think there are many paths to foiling nirvana, you just gotta chose the one that suits. Which is why we have 10,000 kite brands probably :D

For me, low span, low AR, high chord wings seem to have more issues with speed than do higher AR wings with a "nice" anhedral... Your guess is as good as mine!



Plummet said..
More or vertical stabilizer, longer fuse, more stabalizer size comparable to front wing, increased wing size, inc stabilizer aoa.

All these things increase stability with the disadvantage of decreased manuveuribility.

Easiest way to improve stability with your current set up is to shim the rear stab to increase aoa.


He's talking specifically about roll stability.


I know. Those things I mentioned will affect role stability. Try shimming one of your foils for ****s and giggles. See how it feels. You can easily shim by placing some duct tape behind that back screw (assuming your stab is mounted on the top of the fuse).

It takes a couple of minutes and will make an interesting and noticable impact.

snalberski
WA, 576 posts
5 Jun 2018 10:35AM
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As is evidenced by the varied responses above the best person to speak to for an accurate factual answer would be a experienced kiteboarding hydrofoil designer. I can't imagine it would be difficult to obtain contact details of a willing designer who would be happy to answer any questions concisely backed by first-hand RD, education and experience.
My guess is that there are innumerable factors affecting performance and much like kite design its a rob peter to pay paul reality.
The design of my JShapes freeride front wing is a continuous arc and all I know about the design is it rises early, goes fast and carves well which ultimately is all the information I need (though it is valuable to know why).

ActionSportsWA
WA, 580 posts
5 Jun 2018 10:45AM
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Hi Lambie,

In terms of "Roll" stability, the width of wing and aspect ratio play the most important part. The foil profile is also very important. The problem is, you haven't really mentioned if you are surfing, racing or just freeriding. The narrower the wingspan the quicker it will be to roll from side to side. but surface area should be increased by a longer chord length, ie lower aspect ratio. Lower aspect foils are generally slower foils and more manoevreable. The deeper the profile and more rounded the leading edge, the more stall resistant it will be. Pitch stability is controlled by the size of the stabilizer and the length of the fuselage.

The biggest determining factor in roll stability, is the mast length. The shorter the mast, the more stable you will feel in terms of roll. If you can imagine, the centre of roll is roughly in the centre of the fuselage, the higher you are above the centre of roll axis, the more unstable you will be. For surf and high agility (carving) riding, go with a 60-70cm mast, for general freeride, a 70-90cm will be the best all round setup, for going fast and racing, go with the 100-110cm mast.

DM

Kamikuza
QLD, 3441 posts
5 Jun 2018 9:59PM
Thumbs Up

Select to expand quote
Plummet said..
I know. Those things I mentioned will affect role stability. Try shimming one of your foils for ****s and giggles. See how it feels. You can easily shim by placing some duct tape behind that back screw (assuming your stab is mounted on the top of the fuse).

It takes a couple of minutes and will make an interesting and noticable impact.


Vertical stab, fuse length: yaw (and tracking).
Horizontal stab area: drag and pitch response.
Wing size: lift, drag, trim balance, and speed range.
H/Stab AoA: trim balance (foot "pressure").

I know what increasing stab AoA will do -- it'll alter the pitch trim, requiring more front foot "pressure" and will raise the stall speed. You can achieve a similar result by moving the mast mounting point forward, relative to your straps/foot position.

You'll also find that as speed of the wing increases, you'll have to compensate with more and more front foot pressure. May need fast reflexes going into a carving turn to compensate...

Kamikuza
QLD, 3441 posts
5 Jun 2018 10:22PM
Thumbs Up

Also, the horizontal stab can just ruin the whole thing. A lack of "harmony" between the two can make a good wing or whole setup terrible. I tried what became my beloved 720 Axis wing with different empennage at first and it was overall not good. Different rear setup, much better result.

Plus one mast length as per DM.

Plummet
4231 posts
6 Jun 2018 2:52AM
Thumbs Up

Select to expand quote
Kamikuza said..

Plummet said..
I know. Those things I mentioned will affect role stability. Try shimming one of your foils for ****s and giggles. See how it feels. You can easily shim by placing some duct tape behind that back screw (assuming your stab is mounted on the top of the fuse).

It takes a couple of minutes and will make an interesting and noticable impact.



Vertical stab, fuse length: yaw (and tracking).
Horizontal stab area: drag and pitch response.
Wing size: lift, drag, trim balance, and speed range.
H/Stab AoA: trim balance (foot "pressure").

I know what increasing stab AoA will do -- it'll alter the pitch trim, requiring more front foot "pressure" and will raise the stall speed. You can achieve a similar result by moving the mast mounting point forward, relative to your straps/foot position.

You'll also find that as speed of the wing increases, you'll have to compensate with more and more front foot pressure. May need fast reflexes going into a carving turn to compensate...


Moving the mast forward and back is not the same as changing the stab aoa. It wont change the foil stability at all. Changing stab aoa will.
It sounds like you have never adjusted stab aoa.

Try it and see. Increase, decrease. See what the changes are. See whether factory settings are best for your style or not.

You will be able to take the foil from very dynamic to very stable all within a few degrees of adjustment.

What do you have to lose?

Worst case scenario is that you discover the factory setting is best. Best case scenario is that you find you enjoy a slight adjustment better for your style.

I have spent some time adjusting my stab aoa. I had too as I made my own foil. But during that process I discovered that as I progressed in skill and my riding style changed, The stability and maneuverability I wanted out of the foil also changed. I now trimming for less and less stability and more and more maneuverability. Its made a huge difference to how the foil rides and what i can do on the foil.


I think many people who buy production foils never make any adjustments. They ride the foil, if it doesnt suit their needs they sell it and buy another. Assuming all along that the factory setting is best. The factory setting will optimised for general use. However, if you wants and needs are slight different that Mr Joe average then the settings may not be optimised for you.

It sound like lambie is in the learning phase and could do with extra stability right now. I super easy way to immediately improve the stability of his foil is to chunk .5 degree of additional stab aoa. He will be amazed at the immediate additional stability. He can then back the aoa back as he improves.

Here's some vids that will help understand and adjust stab aoa.







Kamikuza
QLD, 3441 posts
6 Jun 2018 10:11AM
Thumbs Up

Select to expand quote
Plummet said..


Kamikuza said..



Plummet said..
I know. Those things I mentioned will affect role stability. Try shimming one of your foils for ****s and giggles. See how it feels. You can easily shim by placing some duct tape behind that back screw (assuming your stab is mounted on the top of the fuse).

It takes a couple of minutes and will make an interesting and noticable impact.





Vertical stab, fuse length: yaw (and tracking).
Horizontal stab area: drag and pitch response.
Wing size: lift, drag, trim balance, and speed range.
H/Stab AoA: trim balance (foot "pressure").

I know what increasing stab AoA will do -- it'll alter the pitch trim, requiring more front foot "pressure" and will raise the stall speed. You can achieve a similar result by moving the mast mounting point forward, relative to your straps/foot position.

You'll also find that as speed of the wing increases, you'll have to compensate with more and more front foot pressure. May need fast reflexes going into a carving turn to compensate...




Moving the mast forward and back is not the same as changing the stab aoa. It wont change the foil stability at all. Changing stab aoa will.
It sounds like you have never adjusted stab aoa.

Try it and see. Increase, decrease. See what the changes are. See whether factory settings are best for your style or not.

You will be able to take the foil from very dynamic to very stable all within a few degrees of adjustment.

What do you have to lose?

Worst case scenario is that you discover the factory setting is best. Best case scenario is that you find you enjoy a slight adjustment better for your style.

I have spent some time adjusting my stab aoa. I had too as I made my own foil. But during that process I discovered that as I progressed in skill and my riding style changed, The stability and maneuverability I wanted out of the foil also changed. I now trimming for less and less stability and more and more maneuverability. Its made a huge difference to how the foil rides and what i can do on the foil.


I think many people who buy production foils never make any adjustments. They ride the foil, if it doesnt suit their needs they sell it and buy another. Assuming all along that the factory setting is best. The factory setting will optimised for general use. However, if you wants and needs are slight different that Mr Joe average then the settings may not be optimised for you.

It sound like lambie is in the learning phase and could do with extra stability right now. I super easy way to immediately improve the stability of his foil is to chunk .5 degree of additional stab aoa. He will be amazed at the immediate additional stability. He can then back the aoa back as he improves.

Here's some vids that will help understand and adjust stab aoa.










Of course it's not the same thing, but it has the same result.

That guy must be completely baffled by the guys riding with only a front wing...

But pitch stability still isn't roll stability.

oldbones
QLD, 89 posts
6 Jun 2018 2:03PM
Thumbs Up

Select to expand quote
Kamikuza said..

Plummet said..



Kamikuza said..




Plummet said..
I know. Those things I mentioned will affect role stability. Try shimming one of your foils for ****s and giggles. See how it feels. You can easily shim by placing some duct tape behind that back screw (assuming your stab is mounted on the top of the fuse).

It takes a couple of minutes and will make an interesting and noticable impact.






Vertical stab, fuse length: yaw (and tracking).
Horizontal stab area: drag and pitch response.
Wing size: lift, drag, trim balance, and speed range.
H/Stab AoA: trim balance (foot "pressure").

I know what increasing stab AoA will do -- it'll alter the pitch trim, requiring more front foot "pressure" and will raise the stall speed. You can achieve a similar result by moving the mast mounting point forward, relative to your straps/foot position.

You'll also find that as speed of the wing increases, you'll have to compensate with more and more front foot pressure. May need fast reflexes going into a carving turn to compensate...





Moving the mast forward and back is not the same as changing the stab aoa. It wont change the foil stability at all. Changing stab aoa will.
It sounds like you have never adjusted stab aoa.

Try it and see. Increase, decrease. See what the changes are. See whether factory settings are best for your style or not.

You will be able to take the foil from very dynamic to very stable all within a few degrees of adjustment.

What do you have to lose?

Worst case scenario is that you discover the factory setting is best. Best case scenario is that you find you enjoy a slight adjustment better for your style.

I have spent some time adjusting my stab aoa. I had too as I made my own foil. But during that process I discovered that as I progressed in skill and my riding style changed, The stability and maneuverability I wanted out of the foil also changed. I now trimming for less and less stability and more and more maneuverability. Its made a huge difference to how the foil rides and what i can do on the foil.


I think many people who buy production foils never make any adjustments. They ride the foil, if it doesnt suit their needs they sell it and buy another. Assuming all along that the factory setting is best. The factory setting will optimised for general use. However, if you wants and needs are slight different that Mr Joe average then the settings may not be optimised for you.

It sound like lambie is in the learning phase and could do with extra stability right now. I super easy way to immediately improve the stability of his foil is to chunk .5 degree of additional stab aoa. He will be amazed at the immediate additional stability. He can then back the aoa back as he improves.

Here's some vids that will help understand and adjust stab aoa.











Of course it's not the same thing, but it has the same result.

That guy must be completely baffled by the guys riding with only a front wing...

But pitch stability still isn't roll stability.


To my mind aoa is either correct or not. When aoa is correct, weighting of feet should be same or similar from 10-30 knots. If as speed increases board wants to dive or lift aoa is incorrect. In my experience the mast is often moved to counter incorrect aoa and conversely the aoa is often moved to counter incorrect mast position. These measures appear to work at lesser speeds. Correct aoa is the most stable.

Plummet
4231 posts
6 Jun 2018 12:46PM
Thumbs Up

Select to expand quote
Kamikuza said..

Plummet said..



Kamikuza said..




Plummet said..
I know. Those things I mentioned will affect role stability. Try shimming one of your foils for ****s and giggles. See how it feels. You can easily shim by placing some duct tape behind that back screw (assuming your stab is mounted on the top of the fuse).

It takes a couple of minutes and will make an interesting and noticable impact.






Vertical stab, fuse length: yaw (and tracking).
Horizontal stab area: drag and pitch response.
Wing size: lift, drag, trim balance, and speed range.
H/Stab AoA: trim balance (foot "pressure").

I know what increasing stab AoA will do -- it'll alter the pitch trim, requiring more front foot "pressure" and will raise the stall speed. You can achieve a similar result by moving the mast mounting point forward, relative to your straps/foot position.

You'll also find that as speed of the wing increases, you'll have to compensate with more and more front foot pressure. May need fast reflexes going into a carving turn to compensate...





Moving the mast forward and back is not the same as changing the stab aoa. It wont change the foil stability at all. Changing stab aoa will.
It sounds like you have never adjusted stab aoa.

Try it and see. Increase, decrease. See what the changes are. See whether factory settings are best for your style or not.

You will be able to take the foil from very dynamic to very stable all within a few degrees of adjustment.

What do you have to lose?

Worst case scenario is that you discover the factory setting is best. Best case scenario is that you find you enjoy a slight adjustment better for your style.

I have spent some time adjusting my stab aoa. I had too as I made my own foil. But during that process I discovered that as I progressed in skill and my riding style changed, The stability and maneuverability I wanted out of the foil also changed. I now trimming for less and less stability and more and more maneuverability. Its made a huge difference to how the foil rides and what i can do on the foil.


I think many people who buy production foils never make any adjustments. They ride the foil, if it doesnt suit their needs they sell it and buy another. Assuming all along that the factory setting is best. The factory setting will optimised for general use. However, if you wants and needs are slight different that Mr Joe average then the settings may not be optimised for you.

It sound like lambie is in the learning phase and could do with extra stability right now. I super easy way to immediately improve the stability of his foil is to chunk .5 degree of additional stab aoa. He will be amazed at the immediate additional stability. He can then back the aoa back as he improves.

Here's some vids that will help understand and adjust stab aoa.











Of course it's not the same thing, but it has the same result.

That guy must be completely baffled by the guys riding with only a front wing...

But pitch stability still isn't roll stability.


Argh. Moving the mast forward and back does not have the same result.

Try adjusting the stab angle and see what happens. You will then understand. Until then, you think you know, but you don't.

Plummet
4231 posts
6 Jun 2018 1:01PM
Thumbs Up

Select to expand quote
oldbones said..

Kamikuza said..


Plummet said..




Kamikuza said..





Plummet said..
I know. Those things I mentioned will affect role stability. Try shimming one of your foils for ****s and giggles. See how it feels. You can easily shim by placing some duct tape behind that back screw (assuming your stab is mounted on the top of the fuse).

It takes a couple of minutes and will make an interesting and noticable impact.







Vertical stab, fuse length: yaw (and tracking).
Horizontal stab area: drag and pitch response.
Wing size: lift, drag, trim balance, and speed range.
H/Stab AoA: trim balance (foot "pressure").

I know what increasing stab AoA will do -- it'll alter the pitch trim, requiring more front foot "pressure" and will raise the stall speed. You can achieve a similar result by moving the mast mounting point forward, relative to your straps/foot position.

You'll also find that as speed of the wing increases, you'll have to compensate with more and more front foot pressure. May need fast reflexes going into a carving turn to compensate...






Moving the mast forward and back is not the same as changing the stab aoa. It wont change the foil stability at all. Changing stab aoa will.
It sounds like you have never adjusted stab aoa.

Try it and see. Increase, decrease. See what the changes are. See whether factory settings are best for your style or not.

You will be able to take the foil from very dynamic to very stable all within a few degrees of adjustment.

What do you have to lose?

Worst case scenario is that you discover the factory setting is best. Best case scenario is that you find you enjoy a slight adjustment better for your style.

I have spent some time adjusting my stab aoa. I had too as I made my own foil. But during that process I discovered that as I progressed in skill and my riding style changed, The stability and maneuverability I wanted out of the foil also changed. I now trimming for less and less stability and more and more maneuverability. Its made a huge difference to how the foil rides and what i can do on the foil.


I think many people who buy production foils never make any adjustments. They ride the foil, if it doesnt suit their needs they sell it and buy another. Assuming all along that the factory setting is best. The factory setting will optimised for general use. However, if you wants and needs are slight different that Mr Joe average then the settings may not be optimised for you.

It sound like lambie is in the learning phase and could do with extra stability right now. I super easy way to immediately improve the stability of his foil is to chunk .5 degree of additional stab aoa. He will be amazed at the immediate additional stability. He can then back the aoa back as he improves.

Here's some vids that will help understand and adjust stab aoa.












Of course it's not the same thing, but it has the same result.

That guy must be completely baffled by the guys riding with only a front wing...

But pitch stability still isn't roll stability.



To my mind aoa is either correct or not. When aoa is correct, weighting of feet should be same or similar from 10-30 knots. If as speed increases board wants to dive or lift aoa is incorrect. In my experience the mast is often moved to counter incorrect aoa and conversely the aoa is often moved to counter incorrect mast position. These measures appear to work at lesser speeds. Correct aoa is the most stable.


Correct at what speed? And for what riding style?.

Your speed, style and desired livelyness v stability vary from individual to individual. What is correct for you might not be for someone else.

Optimal aoa is not the most stable. It's a compromise between maneuverability and stability.

oldbones
QLD, 89 posts
6 Jun 2018 3:12PM
Thumbs Up

Select to expand quote
Plummet said..

oldbones said..


Kamikuza said..



Plummet said..





Kamikuza said..






Plummet said..
I know. Those things I mentioned will affect role stability. Try shimming one of your foils for ****s and giggles. See how it feels. You can easily shim by placing some duct tape behind that back screw (assuming your stab is mounted on the top of the fuse).

It takes a couple of minutes and will make an interesting and noticable impact.








Vertical stab, fuse length: yaw (and tracking).
Horizontal stab area: drag and pitch response.
Wing size: lift, drag, trim balance, and speed range.
H/Stab AoA: trim balance (foot "pressure").

I know what increasing stab AoA will do -- it'll alter the pitch trim, requiring more front foot "pressure" and will raise the stall speed. You can achieve a similar result by moving the mast mounting point forward, relative to your straps/foot position.

You'll also find that as speed of the wing increases, you'll have to compensate with more and more front foot pressure. May need fast reflexes going into a carving turn to compensate...







Moving the mast forward and back is not the same as changing the stab aoa. It wont change the foil stability at all. Changing stab aoa will.
It sounds like you have never adjusted stab aoa.

Try it and see. Increase, decrease. See what the changes are. See whether factory settings are best for your style or not.

You will be able to take the foil from very dynamic to very stable all within a few degrees of adjustment.

What do you have to lose?

Worst case scenario is that you discover the factory setting is best. Best case scenario is that you find you enjoy a slight adjustment better for your style.

I have spent some time adjusting my stab aoa. I had too as I made my own foil. But during that process I discovered that as I progressed in skill and my riding style changed, The stability and maneuverability I wanted out of the foil also changed. I now trimming for less and less stability and more and more maneuverability. Its made a huge difference to how the foil rides and what i can do on the foil.


I think many people who buy production foils never make any adjustments. They ride the foil, if it doesnt suit their needs they sell it and buy another. Assuming all along that the factory setting is best. The factory setting will optimised for general use. However, if you wants and needs are slight different that Mr Joe average then the settings may not be optimised for you.

It sound like lambie is in the learning phase and could do with extra stability right now. I super easy way to immediately improve the stability of his foil is to chunk .5 degree of additional stab aoa. He will be amazed at the immediate additional stability. He can then back the aoa back as he improves.

Here's some vids that will help understand and adjust stab aoa.













Of course it's not the same thing, but it has the same result.

That guy must be completely baffled by the guys riding with only a front wing...

But pitch stability still isn't roll stability.




To my mind aoa is either correct or not. When aoa is correct, weighting of feet should be same or similar from 10-30 knots. If as speed increases board wants to dive or lift aoa is incorrect. In my experience the mast is often moved to counter incorrect aoa and conversely the aoa is often moved to counter incorrect mast position. These measures appear to work at lesser speeds. Correct aoa is the most stable.



Correct at what speed? And for what riding style?.

Your speed, style and desired livelyness v stability vary from individual to individual. What is correct for you might not be for someone else.

Optimal aoa is not the most stable. It's a compromise between maneuverability and stability.



Correct for all speeds. It may be that using aoa to provide stability is covering for deficiencies in other areas of your foils design (what foil are you riding)? Am thinking the type of foil you choose to ride is more so what compliments your style.

Lambie
VIC, 698 posts
6 Jun 2018 7:05PM
Thumbs Up

Thanks for all of the replies - it makes for a interesting read and adds to my information overload LOL !!

I got out late this arvo - but in 8 to 10 knots with my Zeeko Bullet and an 11m Bandit kite - Im amazed I could cruise around on both tacks for an hour ! Ive never been out in that windspeed !

Today Ive started playing with serious upwind and down wind riding - not quite s-bends but at least geting the chance to thinking more about direction change than just height control !!! - im using the race wing which has the dihedral and I think is a bit wider but higher aspect than the Carver wing. As Ral Inn says the higher Im riding the looser the ride!! At this stage I cant pick the difference between the 2 front wings other than the Carver wing seems more pitch sensitive? So listening to Delta Hydrofoil vid above it makes sense that with a higher stabiliser AOA it makes the foil less weight / pitch sensitive but also it comes with more drag (thats not a big probelm for me at this stage!!)

Back to the roll stability - holy crap if I use toe or heal side pressure (first time trying today) it will turn but the other effect is more lift so need to control with height in the turn!!

A lot of this roll rate (length of the wings) and extra lift in turns (speed over the wings) I know from years of gliding but didnt realise how it relates to the foil Im now trying to ride !!

Im still pinching myself I had a session this arvo with a moderate size kite (11m) and a foil and all in around 10 knots!!

bigtone667
NSW, 955 posts
6 Jun 2018 8:16PM
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Select to expand quote
Lambie said..
Thanks for all of the replies - it makes for a interesting read and adds to my information overload LOL !!

I got out late this arvo - but in 8 to 10 knots with my Zeeko Bullet and an 11m Bandit kite - Im amazed I could cruise around on both tacks for an hour !

Im still pinching myself I had a session this arvo with a moderate size kite (11m) and a foil and all in around 10 knots!!


The low wind opportunities become a heap of fun.

And......you still have a few knots to go...

Kamikuza
QLD, 3441 posts
6 Jun 2018 9:45PM
Thumbs Up

Select to expand quote
Plummet said..

Argh. Moving the mast forward and back does not have the same result.

Try adjusting the stab angle and see what happens. You will then understand. Until then, you think you know, but you don't.


How would you know? Your foil is bolted to the board in one place.

Kamikuza
QLD, 3441 posts
6 Jun 2018 10:34PM
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oldbones said..

Plummet said..


oldbones said..



Kamikuza said..

Of course it's not the same thing, but it has the same result.

That guy must be completely baffled by the guys riding with only a front wing...

But pitch stability still isn't roll stability.


To my mind aoa is either correct or not. When aoa is correct, weighting of feet should be same or similar from 10-30 knots. If as speed increases board wants to dive or lift aoa is incorrect. In my experience the mast is often moved to counter incorrect aoa and conversely the aoa is often moved to counter incorrect mast position. These measures appear to work at lesser speeds. Correct aoa is the most stable.


Correct at what speed? And for what riding style?.

Your speed, style and desired livelyness v stability vary from individual to individual. What is correct for you might not be for someone else.

Optimal aoa is not the most stable. It's a compromise between maneuverability and stability.



Correct for all speeds. It may be that using aoa to provide stability is covering for deficiencies in other areas of your foils design (what foil are you riding)? Am thinking the type of foil you choose to ride is more so what compliments your style.


Right. I was hoping an engineer or a pilot would chime in...

While riding we have no control over the surfaces themselves and alter trim by weight shift, like a hang glider.

If you insist on standing in a certain position and can't or won't move your mast, then your only (easy) option to overcome poor weight distribution is to alter the AoA on the rear stab.

Both mast-moving and stab AoA will be felt as a change of "pressure" distribution on your feet -- you've permanently altered the trim of the foil relative to your position on the board.

Why is the Delta guy talking about altering the AoA on the stab? Because a Tuttle box can't be moved.

RAL INN
VIC, 2559 posts
7 Jun 2018 6:24AM
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There are many ways of looking at this.
but from an Aircraft point of view
the rear stabiliser doe the same thing but is controlled in its angle of attack by the pilot.
Simply put it pushes down to compensate for fore aft changes in CoG due to different weights in cabin fuel loads etc.
Now the overall stability is determined by this balance of the 2 downward forces.
the upward force is the lift of main wing.
Now inherent stability can be increased much like a tight rope walker uses a balance beam in that the further apart the two downwards forces are the less impact changes in one or the other have, or at least the rate of effect.

But more stability as in 747 means low manoeuvrability. Low Stability means high manoeuvrability ie: Pitts Special

RAL INN
VIC, 2559 posts
7 Jun 2018 8:33AM
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ROLL Stability is ( focused on the word Stability) is the resistance to change in attitude along the fore aft centre line of the vessel.
on a hydrofoil this line is for the point of this exercise the fuselage front to rear.
the resistance comes from the resistance of the mast and wings, to sideways movement through water.
So the more wing area and mast area pushing through water the more resistance. More roll stability. Or distance from fuselage.

where new hydro foilers come to this hurdle it is usually the process of getting brains to focus on the fact that you are standing on a board that is nearly a metre above the roll centreline. And by far exerting the most leverage on the unit.

It is when you click on this and start controlling roll from the fuselage and not the board. Plus this getting filed into muscle memory that Roll Stability becomes less and less an issue.

Kamikuza
QLD, 3441 posts
7 Jun 2018 10:06AM
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RAL INN said..
There are many ways of looking at this.
but from an Aircraft point of view
the rear stabiliser doe the same thing but is controlled in its angle of attack by the pilot.
Simply put it pushes down to compensate for fore aft changes in CoG due to different weights in cabin fuel loads etc.
Now the overall stability is determined by this balance of the 2 downward forces.
the upward force is the lift of main wing.
Now inherent stability can be increased much like a tight rope walker uses a balance beam in that the further apart the two downwards forces are the less impact changes in one or the other have, or at least the rate of effect.

But more stability as in 747 means low manoeuvrability. Low Stability means high manoeuvrability ie: Pitts Special


You mean the trim system, but I didn't want to bring aircraft into this because it muddies the waters.

Aircraft with movable horizontal stabilizers (mostly supersonic military aircraft) alter the AoA of the stab... (Airliners use a movable tailplane for trim to adjust angle of incidence to account for shifting CoG as fuel is burned.)
Most aircraft use hinged elevators to alter the lift vector of the tailplane...
...and create a moment just aft of the aircraft's center of gravity, giving the pilot pitch control.

With the KBHF, we're shifting our weight around the center of gravity to create the moment, more like a hang glider but with the benefit of a horizontal stab adding stability.

RAL INN
VIC, 2559 posts
7 Jun 2018 10:21AM
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The rear wing on aircraft is the stabiliser and the moving surface the Elevator/s
when whole thing moves it's a Stabilator and was a feature of The Piper Warriors. One of the planes I learned to fly in.

from those days "trim system" was a wheel that you used to adjust another mini elevator on back of elevator to fine tune balance so you could fly hands free

And on the Roll Stability thing. Dihedral increased roll stability.
probably a gravity thing as it lowered the CoG in relation to the CoL

Kamikuza
QLD, 3441 posts
7 Jun 2018 10:53AM
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RAL INN said..
The rear wing on aircraft is the stabiliser and the moving surface the Elevator/s
when whole thing moves it's a Stabilator and was a feature of The Piper Warriors. One of the planes I learned to fly in.

from those days "trim system" was a wheel that you used to adjust another mini elevator on back of elevator to fine tune balance so you could fly hands free

And on the Roll Stability thing. Dihedral increased roll stability.
probably a gravity thing as it lowered the CoG in relation to the CoL


Yes

Plummet
4231 posts
8 Jun 2018 2:08AM
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Ral Inn, Old bones, Kamizuka.

Have any of you actually tried adjusting the stabilizer aoa?

If not I suggest you go and try it. It will only take a couple of minutes to shim the rear stab with some duct tape.
Shim it, try it, adjust it. Test to the extremes to see the effect it has.

What do you have to lose? a session or 2 testing different settings.
Report back what you found.
Worst case scenario is that you find the manufactures settings is best!. If they have done their job right it should be.
Best case scenario is that you find a slight shimming of the foil improves the ride for your style.

On a side note. What about manufacturing tolerances of these foils? what is the design stab aoa compared to actual manufacture aoa?
What tolerance +/- do these chinese manufactuers work too? Even if the design aoa is perfect, manufacturing processes are not.

Get in there and do some testing!

Plummet
4231 posts
8 Jun 2018 2:30AM
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Lambie said..
Thanks for all of the replies - it makes for a interesting read and adds to my information overload LOL !!

I got out late this arvo - but in 8 to 10 knots with my Zeeko Bullet and an 11m Bandit kite - Im amazed I could cruise around on both tacks for an hour ! Ive never been out in that windspeed !

Today Ive started playing with serious upwind and down wind riding - not quite s-bends but at least geting the chance to thinking more about direction change than just height control !!! - im using the race wing which has the dihedral and I think is a bit wider but higher aspect than the Carver wing. As Ral Inn says the higher Im riding the looser the ride!! At this stage I cant pick the difference between the 2 front wings other than the Carver wing seems more pitch sensitive? So listening to Delta Hydrofoil vid above it makes sense that with a higher stabiliser AOA it makes the foil less weight / pitch sensitive but also it comes with more drag (thats not a big probelm for me at this stage!!)

Back to the roll stability - holy crap if I use toe or heal side pressure (first time trying today) it will turn but the other effect is more lift so need to control with height in the turn!!

A lot of this roll rate (length of the wings) and extra lift in turns (speed over the wings) I know from years of gliding but didnt realise how it relates to the foil Im now trying to ride !!

Im still pinching myself I had a session this arvo with a moderate size kite (11m) and a foil and all in around 10 knots!!


Sounds like you are having fun. Try leading into turns with your upper body. Kinda fall in the direction you want to go rather than trying to use your legs to turn. Like riding a bike around and down a burmed banked corner, You do very little actual steering. you lean into the corner. Try that on the foil and see what happens.

Yes, increasing stab aoa will increase drag and stability. It will give more front foot pressure as well. You may need to move straps or foil position to compensate for that. But it will be more stable for learning. I cranked mine up to 3.5 degrees and it made the learning process easier as I had a definite front foot pressure to fight against. Stability was higher so I could be more course on my weight distribution without ridiculous crashes. It made trying flying foot switches heaps easier. As I progressed I trimmed back the stab aoa to 2.75 deg. That made my foil more sensative, better at speed and more maneuverable. Things I didn't want while learning I now wanted with a bit of experience.

I've managed to take my foil from a sedate learning foil to a snappy responsive wave riding foil with 0.75 Deg stab aoa adjustment.

RAL INN
VIC, 2559 posts
8 Jun 2018 8:28AM
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I have nothing to add to the tune V's leave debate. As I haven't ever bothered past moving straps back as my skill level rose( not that much).
Warwickl has and got the results he wanted, and I respect his opinions.

many times those that voice the most about why not or how come their brand is the only perfect one perhaps don't have the ability to experiment.

I do advocate that changes from Factory specs is best done when your skill levels are at a point that you can tell the difference.

Kamikuza
QLD, 3441 posts
8 Jun 2018 9:23AM
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Plummet said..
Ral Inn, Old bones, Kamizuka.

Have any of you actually tried adjusting the stabilizer aoa?

If not I suggest you go and try it. It will only take a couple of minutes to shim the rear stab with some duct tape.
Shim it, try it, adjust it. Test to the extremes to see the effect it has.

What do you have to lose? a session or 2 testing different settings.
Report back what you found.
Worst case scenario is that you find the manufactures settings is best!. If they have done their job right it should be.
Best case scenario is that you find a slight shimming of the foil improves the ride for your style.

On a side note. What about manufacturing tolerances of these foils? what is the design stab aoa compared to actual manufacture aoa?
What tolerance +/- do these chinese manufactuers work too? Even if the design aoa is perfect, manufacturing processes are not.

Get in there and do some testing!


You move your mast first.

I don't need to do it *again* because I know what result it'll have because physics. AND I can achieve the same effect without adding any problems. Think about it for a bit then get back to us.

Manufacturing tolerances LOL

Kamikuza
QLD, 3441 posts
8 Jun 2018 10:21AM
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Plummet said..

Yes, increasing stab aoa will increase drag and stability. It will give more front foot pressure as well. You may need to move straps or foil position to compensate for that. But it will be more stable for learning. I cranked mine up to 3.5 degrees and it made the learning process easier as I had a definite front foot pressure to fight against. Stability was higher so I could be more course on my weight distribution without ridiculous crashes. It made trying flying foot switches heaps easier. As I progressed I trimmed back the stab aoa to 2.75 deg. That made my foil more sensative, better at speed and more maneuverable. Things I didn't want while learning I now wanted with a bit of experience.

I've managed to take my foil from a sedate learning foil to a snappy responsive wave riding foil with 0.75 Deg stab aoa adjustment.


You should add that you made your own foil from your own designs and hadn't ridden a foil before and can't move the mast or straps IIRC.

With a good production foil, you'll probably find out that they've ironed out all the idiosyncrasies of the design and the problem is then between the kite and the board...



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"Stable vs unstable foils - Front wing shape?" started by Lambie