Why a stabi, when wing foiling?

[fluidity]

Dontsink,
Interesting point about the wingtips, I hadn't really considered it. However, this is only applicable for the volume passing inside the box section. Note that the top of the box and the underside at the tips both allow clean escape the side of water that then provides no more lift. On the top it's not much of an issue because air+water pressure holds the water to the wing contributing slightly more lift. On the underside it is an issue but the issue is subject to compromise in structural integrity of the box wing cross section shown.
I suspect the design is avoided on aircraft because of what looks like a higher weight to lift ratio of the wing itself in comparison with a single wing. Under water, this weight become rather insignificant.
I do like the possibility to have better control from breach due to the upper wing section breaching in advance but does it work in practice?

[fluidity]

Note, that the propsed desing by Dontsink is a infinity wing, not a biplane wing. (The one in the video might be a bit closer to biplane than infinity). But theory shows that infinity wings have great potensial. If designed well....

I don't have an aviation history so I'd be quite happy calling it a biplane with closed tips. "Infinity wing" sounds like a marketing ploy! Though it seems to be preferred terminology
Technically you could also call it a quad plane, or for the infinity wings I looked at on youtube, a hex wing. It doesn't LOOK like a monoplane, but if the surface wraps all the way around, like with a ring? Does that make it actually a monoplane? Or maybe we just count the lift surfaces? in which case it's a specific version of a biplane

I found this about an RC plane flaunting one on youtube:
By Request, I have put together some additional flight footage of the X-100 Infinity Wing 3D printed RC aircraft. There is music in the intro and outro but it fades away during the flight footage to leave only the raw audio. It hand launches well at full throttle but does require a little stronger throw than you may be used to, in order to get the speed up right away.

This might even be preferable in kite foiling, to have a smoother transition of lift?
But it also highlights the probable higher stall speed, indicating more of a challenge for wingsurf hydrofoiling.

[Peter_Frank]

C'mon not an Infinity wing, but as said a biplane wing with all its performance drawbacks

Peter

[PrfctChaos]

At some stage in the future you slow wingfoilers will all be on biplane / boxwing / infinity wing designs, or anyone that needs to foil at SLOW speeds in water. That is a 100% fact, you can take it to the bank. Foil manufacturers are still just catching up, or more likely the current manufacturers might be light on theory and heavy on manufacturing.

For anyone following the other wing design thread. You would be well aware that lift induced drag is the real hurdle to overcome for SLOW speed foiling (Winging is a prime example). As can be seen by the very large wings used in general.
viewtopic.php?f=107&t=2407467&start=120

The most practical way to battle the high induced drag at SLOW speeds is to increase wingspan. But obviously big wingspan comes with other compromises (Strength, handling etc.).

Now to qualify my statement about all SLOW foils being box / infinity wings in the future. I will refer you to the below paper, showing that Oswald factors of 1.5-2 should theoretically be possible for this type of wing. Higher oswald factors is a ideal way to reduce lift induced drag and still keep a reasonable wingspan. Read the paper / don't read the paper, belive me / don't believe me, it doesn't make a difference to me at all, I'm not going to start making slow foils anytime soon. I'm more interested in medium - fast foils where induced drag is much less of a problem.

OPerA_PUB_DLRK_12-09-10.pdf

(940.97 KiB) Downloaded 89 times

[Dontsink]

Ok, glad this design has arisen some interest.
Some clarifications and answer to questions:

-The design is not mine and i have no relationship with Bruce, i just found it on youtube by chance.I do see huge potential.

-It is not a classic biplane design like a Pitts or Gipsy Moth aircraft,Horue already tried that.This has closed/joined wingtips.There is a big difference.

-I call it infinity wing because it is commonly named like that in aviation, also boxwing or Prandtl Boxwing (this last one makes me feel really scientifical,i'm not

-The concept has been kicking around in aviation for decades.Some projects are working on it.
As an airline pilot i think a big challenge is making this structure flexible and lightweight, airliner wings have to flex a lot or they would break in turbulence.
At the scale we are dealing with this is not a problem, current foil designs are built as stiff as carbon allows.

-Breaching: in this earlier vid you can see Bruce trying to breach it at 02:30:



It seems to just gently drop down,no cavitation or stall.

-Glider pilots say "You can't cheat aspect ratio".
Airplanes with fancy winglets,sharklets etc... would be more efficient and lighter if you flattened those tips increasing span.
I guess the same would apply to a boxwing.Every bend you put on an aerodynamic or hydrodynamic surface creates interference drag.
But the safety & maneuvrability & compactness & breaching improvement that the boxwing brings could make it a winner IMHO.
Hi Aspect wings are pointy sharp, unforgiving and not very surfy.They roll slow and the big span brings tips out of the water if you turn hard.They have great glide...period.
Kiters can happily go on <1000cm2 foils so the spans are acceptable, but for winging you are dealing with 1m spans ...not much fun i think.

-Stall: i do not know the stall behaviour of the boxwing foil.I do not think it wil be very different from a monoplane but i've been wrong before ,many times . Testing will tell.

-That paper about Oswald numbers is over my pay grade, i will try to read it though.
After +20 years of flying for a living i admit that i do not know why airplanes fly, yeah you can laugh . But i am not alone in my ignorance
https://www.scientificamerican.com/arti ... n-the-air/

Ride on!

[Peter_Frank]

The box wing concept is interesting indeed, although also controversial.
We will see.

But if the wings are almost over each other like on the picture, you don't gain pitch stability.

If offset so one wing swept a lot behind the other, you can obtain stability, and this thread is about stabless riding, so key is stability.
Offset wing more stable will have downsides in terms of performance I would think, but the concept resembles the canard principle, so viable outcomes might be possible as I see it .

The box foil in the picture also has a stab.

Peter

[fluidity]

The box wing concept is interesting indeed, although also controversial.
We will see.

But if the wings are almost over each other like on the picture, you don't gain pitch stability.

If offset so one wing swept a lot behind the other, you can obtain stability, and this thread is about stabless riding, so key is stability.
Offset wing more stable will have downsides in terms of performance I would think, but the concept resembles the canard principle, so viable outcomes might be possible as I see it .

The box foil in the picture also has a stab.

Peter

I think there's a practical limitation for offset difference due to poorer yaw control as the box tip closure pieces have to be longer for a longer offset.
Also, the purported advantages of tip closure are essentially lost if upper and lower wings are too far offset from each other. It might be more practical to use similar sixed front wing and stabiliser wing, but placed at different heights, closer to each other and with the stabiliser also optimised for lift.

[Dontsink]

The box wing concept is interesting indeed, although also controversial.
We will see.

But if the wings are almost over each other like on the picture, you don't gain pitch stability.

If offset so one wing swept a lot behind the other, you can obtain stability, and this thread is about stabless riding, so key is stability.
Offset wing more stable will have downsides in terms of performance I would think, but the concept resembles the canard principle, so viable outcomes might be possible as I see it .

The box foil in the picture also has a stab.

Peter

You are right, and again,sorry for steering this thread off the rails.

To get back on stabless track,here is a stabless version of the boxwing in an RC glider (As mentioned in previous post by Fluidity):



He does say it needed a bigger than expected initial push but IMHO this is due to the tail heaviness of the design ,they are still playing around with the best CG position.

But i do not think this stabless version of the boxwing will be pump-able , a must for surf application.

[Horst Sergio]

About how much monofoiling depends from skill,
the following statement from a friend is essential to know, that's what he told me:

"The day I tried to teach you telemark skiing was the moment I lost all respect for your body control. That was the day I decided to try mono foiling!"

And in fact since then, two years ago, he is only on a duotone monofoil and as just strapless he learned strapless monofoil foot switch (Øyvind style) before I did.

I have yet to see anyone ride one of these better than a normal foil with a stabilizer, regardless of what you consider “best”. Fastest? Highest jump? Best wave ride? All on normal foils.
Why would I ride a monofoil? More difficult with no obvious payoff. ...

Thanks, and agree it is time for a video, even if just lightwind stuff some month ago and with the single strap, so not yet jibing nice. ... It is up to viewer if a benfit can be seen.



And another one from Øyvind, just keep in mind as it looks like he is not winging since long, but already doing his strapless foot switch and also shows pumping, better than I could show with my body cam.



@slowboat:
Would be interesting to hear more about your Delta Mono, as I understand it has a profile designed specific for mono so more stable. Question is will this noticeable make a difference to another wing by improving stability or and at the same time by reducing the glide as known by stable profiles with reflex or offset.

About pumping:
Well I am not sure yet my self, in conclusion yes you can pump but pretty sure worse than with a stabi, which can be a point, but I think it depends a lot from the wing. Had once a prototype which was very small as 700 cm² which felt
extremly well, same as the Moses Onda, all talking about without stabi, naturaly. On the other hand my own low tech gong wings feel pretty bad.
Worst result was that I was not able to stay in movement behind a 55' sailboat on motor, so not creating serious wake.
On the side with the wing in the hand I very often in our gusty lake conditions I am bridge wind holes with well about 100 m with as it feels very low, even with the worse Gong wings and on a inflatable board which also is for sure not the pumping Queen.
Interested to see my self how much better pumping will become when I get my custom from Groove, with its drag will allow to try much more wings.

@fluidity:
Yes would be nice to have foil designs with a detachable back part, so you can switch to a 100% monofoil setup easily, some as f-one already have such a design.
Also high AR wings can be very stable as mono, just have a look in the kite monofoil topic, riding wings up to AR 7.
Fences don't make sense to me in the context, they have just use for surface piercing foils, as many foil sail boats do.

@Okkiteboarder
In fact: Upwind is always the point where you can directly see and compare the performance benefit of a mono, they don't have the best VMG as they have a speed limit, but upwind angle beats everything significantly also when winging. This would be the reason after 10 years without competing, I think about to take part on one of the first wing races (even if a silly disciplin, as winging is not made for racing). Just to see if I can be faster than the stabi guys, on a upwind course, no doupts.

[fluidity]

@fluidity:
Yes would be nice to have foil designs with a detachable back part, so you can switch to a 100% monofoil setup easily, some as f-one already have such a design.
Also high AR wings can be very stable as mono, just have a look in the kite monofoil topic, riding wings up to AR 7.
Fences don't make sense to me in the context, they have just use for surface piercing foils, as many foil sail boats do.

I will have a crack at detaching the back part today and report back whether it's much harder unifoiling than stab foiling with the flexy stab joiner rod. I glued and screwed it in so if it's too much of a mission then I'll wait until my 12mm x 500mm long titanium rod comes before busting it out.
I'm inspired by your successes

Regarding hydrofoil uni-wing choice, I would avoid any of the wing profiles where the trailing edge has a concave undersurface, it seems like looking for trouble if you don't have a stab to counter those foil's dive tendencies.

Some of my new deep plunge CNC bits arrived last week, I'm now contemplating doing a resize of my design for my 1200 x 330 x 75mm wing, make it something more like 800 x 450 x 38, and go stabless, put the mast socket directly into the rear of the wing. That would seem like a comfortable length for learning to unifoil gybe