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Why a stabi, when wing foiling?

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fluidity
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Re: Why a stabi, when wing foiling?

Postby fluidity » Tue Dec 08, 2020 10:07 am

I think I'll just have to make an ultra low aspect ratio foil like the one I designed and posted above and see how it performs in real life. Sometimes book learning is good, other times people get ideas in their heads based more on trends than real world research.
Right now high aspect ratio foils are trending like we are using gliders and on the perception that they are fast and efficient.
Look at the highest speed fighter jet plane shapes though, and they are actually low aspect ratio, high chord. They aren't designed for gliding but they are certainly designed for speed and manouverability. Water is an uncompressible fluid, not quite the same as air and I'm keen to feel how a counter-fashionable hydrofoil performs out of the tea room and computer and under my board. Thickness is also a big part of providing a combination of drag and lift so it will be interesting to see how a narrow span low [thickness:chord ratio] wing performs in practice.:D

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Re: Why a stabi, when wing foiling?

Postby ronnie » Tue Dec 08, 2020 1:15 pm

fluidity wrote:
Tue Dec 08, 2020 10:07 am
I think I'll just have to make an ultra low aspect ratio foil like the one I designed and posted above and see how it performs in real life. Sometimes book learning is good, other times people get ideas in their heads based more on trends than real world research.
Right now high aspect ratio foils are trending like we are using gliders and on the perception that they are fast and efficient.
Look at the highest speed fighter jet plane shapes though, and they are actually low aspect ratio, high chord. They aren't designed for gliding but they are certainly designed for speed and manouverability. Water is an uncompressible fluid, not quite the same as air and I'm keen to feel how a counter-fashionable hydrofoil performs out of the tea room and computer and under my board. Thickness is also a big part of providing a combination of drag and lift so it will be interesting to see how a narrow span low [thickness:chord ratio] wing performs in practice.:D
Low aspect 'foil' design from 1960.
http://mypaipoboards.org/GaylordMiller_Paipo_Foil.shtml
It seems it was used as a planing surface, not underwater, but there might be a way a foil would keep itself just at the surface?

A long chord thin foil is going to be very pitch sensitive?

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Re: Why a stabi, when wing foiling?

Postby nemoz » Tue Dec 08, 2020 3:36 pm

Attached you can find the outline of my mono foil, the blue one is the one i built, just to let you know the "tail" is flat after the mast junction, and is full carbon no foam and my idea was to create a flex tail to increase the pumping ability and to increase manoeuvrability, my idea was to let the final part bend during the carve, I have no idea if it works in reality i mean i have no video prooving the flex under the water.
I was thinking to go for the 1900 900 wide, any suggestion are more than wellcome.
Attachments
Immagine 2020-12-08 152458.jpg

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Peter_Frank
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Re: Why a stabi, when wing foiling?

Postby Peter_Frank » Tue Dec 08, 2020 9:55 pm

Interesting designs and has to be proven in real life, but a bit sceptical...

They are super low AR, and huge non beneficial surface area, meaning draggy with no lift and huge induced drag?

Super lively maybe, if not too slow.

But personally I think I would prefer a clean wing without a stab, instead of one with more drag than a stabbed one, if I had to choose.

It resembles a bird wing, and they are NOT good flyers at all :wink:

Only those with high AR and a small tail(feathers) are reasonable, but no way close to human designed gliders or foils.

Birds, only some of them, has the advantage to twist their wings and change the profile and tips/trailing edge - and they are EXCELLENT at this, That is their advantage.
Not possible with most of our "crafts", but to some extend with slots and flaps and foil kites with camber control.

The advantage of planes and foils though, compared to birds, are we have materials so able to make a much more efficient lower drag wing/foil than the birds, a lot less drag.
As birds need a lot of practical strength leading to the "thick" designs, not flying well, compared.

A soft tail would probably only hinder pumping, instead of being beneficial - just like any softness in a board slows you down and you loose efficiency.

I might be wrong, just my thoughts and experience :roll:

The good thing would be, you could make a safer foil (no pointy ends) that can withstand a lot more abuse and hitting the bottom, eventhough not performing well, but excellent for learning maybe?

But your arms would get tired :-?

8) Peter
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juandesooka
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Re: Why a stabi, when wing foiling?

Postby juandesooka » Wed Dec 09, 2020 12:13 am

I remain intrigued by canards, but not many others are, seems to make sense, but never caught on in any big way. In a way, the no-stab seems related to canard, as the dominant lifting force is directly under back foot. The small front canard wing also lifts, but maybe it's impact is somewhat minimal? So it is a small extension to remove it and only have the big back wing?

The main benefit i see for canard is the turning comes off the back foot, like on a shortboard surfing, rather than steering through turns with the front foot. This gives a more surf-y feel. Is this similar for mono? Or would it be more a pivoting vs a carving feel?

Skimming thread above, the lack of pumping potential with mono seems to be a deal killer for any use other than kiting. Kinda feels like pushing riding unicycles...which are not as effective in any way than bikes, other than pivoting in place maybe. But hey, it's fun to try new stuff and keep things interesting, so Go Man Go!

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Re: Why a stabi, when wing foiling?

Postby PrfctChaos » Wed Dec 09, 2020 7:21 am

juandesooka wrote:
Wed Dec 09, 2020 12:13 am
In a way, the no-stab seems related to canard, as the dominant lifting force is directly under back foot.
Nope, not possible for the effective lifting point of the front wing to be anywhere near the back foot with a mono. If one assumes equal load on front and back foot, then the centre of lift HAS to be closer to the front foot than the back foot when using a mono (in other words you move your feet back a bit when taking of the stabiliser). This is because the load going through your feet are now used to counteract the rotating moment caused by any drag on the foil / fuse / mast. In a traditional foil the stab handles this mostly (if well setup. A balanced foil), which means less weight transfer between going fast / slow. And you stand a bit further forward compared to mono.

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Re: Why a stabi, when wing foiling?

Postby fluidity » Wed Dec 09, 2020 8:15 am

So, doing some more research on this.
The Vought V-173 is an example of a very radical high chord, super low aspect ratio experimental plane. Radical enough that it made a lot of people who knew what real aircraft looked like, deeply uneasy about it's shape.
There's a good discussion of it here:https://oldmachinepress.com/2017/01/20/ ... s-skimmer/ Including mention of the initial test plane being under powered and financial woes affecting the successor version, including a decision that a test flight needed to be made far away but that it would be too difficult to transport it there. Then a wrecking ball came along...
The V-173 exhibited very short take off requirements and potential for high speed. Slightly skewing matters for us, the props effectively increased apparent wind and lift by working over a large proportion of the aircraft's body.
Apparently even at 45 degrees it wouldn't stall! Landing, it would experience a ground-effect further back than the free-flight centre of lift and take a dive. Control requirements were hugely underestimated because in-flight the high chord presented massive stability that required huge effort to overcome for steering and roll. (You don't want to be that test pilot!)

Take a moment to reflect on the Airforce's likely automatic reaction to the test pilot's underwear-staining experience in a profoundly unusual looking plane. All the armed forces primarily recruit Myers Briggs S(sensing), J(judging) types, people stronger in observation, judging and conservatism than in intuition, perceiving and change adaption.

Now lets take a look back at aeronautical reasons to avoid Deltas despite their known superior lift/weight characteristics: and there's a biggie!
Airports the world over work on the basis of runways with a lot of length and short width.
A plane with high aspect ratio can easily control it's roll with ailerons. Approaching a runway with high cross winds, a pilot can compensate for cross wind by keeping the plane flat under aileron control and straight (with rudder)relative to the runway/cross winds(it's a compromise that starts with centre of mass and ends with skidding and paralleling the fuselage with the runway)
A delta plane uses elevons for a combination of pitch and roll control, it doesn't have yaw control but looking from a bird's eye view, yaw is provided by oposing left/right elevon input until the aircraft is partially rolled and then elevator control of pitch(both elevons in the same direction) so that the off-horizontal axis from the roll moment converts the pitch moment to yaw as seen from a bird's eye view. All this works much easier than it sounds but the end result is that yaw changes are done in 3 dimensions for a delta, while for conventional fuselage planes, yaw motions can be done while the plane is still flying in a 2D-plane. This means that for a delta plane, runways approached in high cross winds are very dangerous, a rudder on a delta doesn't get enough leverage and is pretty much a waste of time. I'm mentioning this because the single biggest reason Aviation doesn't use deltas is a safety reason that simply has zero affect in our hydrofoiling use-cases.

None of the above dissuades me from trying my latest design out. As I said, it's intended as a learner unifoil with high pitch stability due to the long chord. The low aspect ratio improves roll control allowing for tighter turns. My gull-wing modification is primarily done for ease of manufacturing but the downward pointing tips should improve wingtip lift performance to my untrained perception by diverting water flow closer in to the longer trapped path. As for aspect ratio and eficiency, it's only part of the picture. I've flown RC gliders including deltas, jets and more traditional glider shapes. Deltas can be very high performance. A swing-wing jet can actively change from a high aspect traditional shape for low speed high lift, to low resistance, high speed delta shape. Note that a longer surface will experience more drag than a shorter surface for the same width but this is not what we are doing, Drag is more about total area, thickness, thickness profile and surface interaction. In a wing with longer chord, fluid molecules close to the wing actually have more distance to speed up, I'm thinking that means a longer chord for the same area has better speed potential. Remember we aren't trying to get ultimate lift at high speed, we want control, glide and LOW speed lift. At high speed lift is more than we need.

Here's the next consideration- a high mass uncompressible fluid vs air. All those of you who've flown a kite in a loop, felt the apparent wind. Wind surfing, you know that feeling of power you get when the sali is no longer stalled but slicing through into new air that hasn't had a chance to slow and stall, it's that new, not yet slowed air mass that is dumping it's moving energy into your attached surfaces. In the air, a high aspect wing, a tall but narrow sail only develops it's power at higher speeds. A lower aspect kite, a shorter but higher chord sail have better low down power. So think about what you want under your feet... do you want max lift at highest speeds?? Imagine that surface cutting through not air, but water. That mass is around 800 x more dense than air. Your required lift comes off a much smaller area, span. Do you really want that "lift optimised for high speed" foil under your feet?

fluidity
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Re: Why a stabi, when wing foiling?

Postby fluidity » Wed Dec 09, 2020 9:15 am

ronnie wrote:
Tue Dec 08, 2020 1:15 pm
A long chord thin foil is going to be very pitch sensitive?
Pitching is stern up, bow down and vice/versa.
Yawing is rotating as seen from bird's eye view.
Rolling is rotating when looking from in front or behind.

A long chord is long from front to back so it's pitching resistant.
A high aspect ratio wing is long from wingtip to wingtip so it resists rolling.

This is a low aspect wing so it's easier to roll, harder to pitch, no stabiliser needed. Like with the Vought V-173 plane, similar, the test pilot had immense difficulty controlling it because it was so stable. In this case, I made the wing to fit a 600 x 450 x 50mm box and that 450 is only at the middle, there's less pitching moment resistance as you get closer to the tips. Certainly It meet's Horst's spec of a single front wing, no stabiliser though I don't think he anticipated someone jumping in with a monofoil wing offering that would be EASIER to ride :lol:

Best I build one, see how it goes and then look at refinements if I like it. I know the board will respond much faster to foot pressure from one side to the other, compared with my massive 1200mm wide wing I have at the moment.. that one gets beyond my ability to correct the roll at times but I'm learning too, just to complicate things.

Something I expected to be able to do but haven't really felt happen with my current wing, is to be able to yaw the wing in motion and have the foil move from site to side under me, bacically to impart roll similarly to controling lean on a bicycle by turning the handle bars. I suspect it's a given with shorter wingspan foils and I expect this one to be particularly easy to control like that. Currently I think it's not happening for me because of my high current wingspan and area, it's quite roll resistant and yawing the wing has little effect because the mast(which is the initiator of roll) is working against the high wingspan and area of the foil.

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Re: Why a stabi, when wing foiling?

Postby ronnie » Wed Dec 09, 2020 10:17 am

Birds are a good guide as to what works - based on evolution limited by also having to live and breed.
We can think outside the box. This is a good example, after all those paper gliders were designed and competed for distance - someone cut up a plastic bottle and threw that.
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Re: Why a stabi, when wing foiling?

Postby Horst Sergio » Thu Dec 10, 2020 6:23 pm

slowboat wrote:
Sun Nov 29, 2020 7:02 pm
... What board are you getting? ...
To get back to topic and answer your question more detailed. This will be my new board a Groove half custom:
The outline, rails and scoop line are from the new serial: "G-fuerte"

https://www.groovekiteboards.it/boards/g-fuerte/
"The G-Fuerte is the latest project made by Groove.
Compact shape with high volume and enough width. Easy to pump with its flat deck and constant volume flow.
Developed and designed in collaboration with Gunnar Biniasch in Fuerteventura."

As also Indiana offers a pretty similar shape in collaboration with Gunnar, I guess there is pretty much Gunnar in both designs.
https://shop.indiana-paddlesurf.ch/foil ... arbon.html

Requested changes especially in perspective to "Mono only" are:
- reducing width even more from 60 to 56 cm (Indiana has 63 cm)
- increasing thickness to 12 cm to keep a volume of above 70 litres
- changing strap position and straps fundament wideness
- pushing the tracks forward as most important for the mono
- removing carrying handle as with a mono you may also grab the strut
- adding the nose handle fundaments, which again Gunnar recommends, not sure if I will use it but gives also the possiblity to install a nose net as on SUPs, to store your lunch or what not :wink:
- standard color pattern to keep corporate identity aspect for Michele
Kitejunkie_Wingboard_150x56x12_G-fuerte.jpg
Interested to see what the weight will be and how much raileis impacts it will withstand, but in stability to weight, Groove seems to be one of, if not the best, from my experience.


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