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Why a stabi, when wing foiling?

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purdyd
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Re: Why a stabi, when wing foiling?

Postby purdyd » Thu Dec 03, 2020 5:33 pm

60A6101D-675B-4633-84E6-AC3C1615B0A1.jpeg
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Let me preface this by saying I really don’t know what I am talking about but here are some thoughts.

I’m seeing a continuing trend to higher aspect front wings and smaller with less downward pressure rear stabilizers.

It would seem to ride stabless you need a delta wing hence lower aspect ratio?

So are you still gaining as much with stabless versus high aspect wings and small more aligned stabs?

As my fuselage shortens and my rear stabilizer keeps getting chopped down am I inching up on riding stabless?

In the aviation world gliders have stabilizers and big ass high aspect wings.

The flying wings are said to have very good lift to drag but as I understand it, it comes from the loss of the vertical stabilizer.

Is there a reason we haven’t seen a flying wing glider? Or at least they aren’t very common.

Is it a mental block?

I pity anyone who rides somewhere that the stabilizer is catching stuff. My experience is that it is the mast. There should be a prize for someone who solves that problem.

I think it really cool that people are pushing the sport with stabless riding. Is there any manufacturer offering an off the shelf solution?

Would wing designed from the ground up be better stabless?

Would something like a cloud 9 f series foil perhaps extendsed in the middle be an ideal stabless wing?
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Re: Why a stabi, when wing foiling?

Postby Peter_Frank » Thu Dec 03, 2020 7:38 pm

Hi

Well, stabless gliders we have flown for years, dont need to be low aspect delta or swept wings (both helps hugely on stability), but can be done on a super high AR straight wing, being just as stable.

But it will require an "S" profile to be stable for flying, and will have downsides in handling and turning also simply because you have no stab leverage.

Fly quite well though, no issues, have flown many of these.

The cost is huge, such a profile can fly ok fast and have reasonably low drag, but if you want to have good lift, AND low drag, which is what gliding is all about, to get low sink rate and even more important, max glide, they are pretty useless.

Compared to a fuselage and a small stab - here you gain so much in terms of stability and agility/turning, at almost very low expense (fuselage tail and stab drag), compared to a stabless that in total are a lot worse in terms of lift and lift/drag.


BUT, the interesting thing for hydrofoilin is, if you are sufficiently "fast" reacting, which can be practized into muscle memory, maybe even with low talent, then a hydrofoil is controlled in another way, because of weight balance.
Another surprisingly good effect is the long mast, which is actually dampening the wrong torque of a stabless wing - which we know from having a longer mast makes it actually more stable, compared to a short one.
Reason why we think opposite, is because most or all beginner foils with supershort masts have a bigger stab and or more negative stab lift - so a lot more stable, besides you will never notice if stable or not, as you touch down every now and then with these.
If too long the ability to correct fast is lost though, like a unicycle very high.

Above means you can not compare to a glider/aircraft, where it has to be either self stable, or at least controlled by rudders and not weight.


A hangglider is controlled by weight balancing, but it also needs a combo of semi S shaped profile, combined with wing sweep, or wing sweep with washout, to be sufficiently stable and not a death trap - this is why they have more limited performance, apart from the structural downsides and drag of the pilot.


I also pity those few having a "stab catching weed" things where they ride - I have never had that, actually almost never on my wing either, always on my mast it is a problem with the weeds we got.
On occasion you can hit a big lump of weed yes, but here you go faceplant immediately - no matter what and stab or not :rollgrin:
So much weed that it catches the wing also, then it has been over much earlier for any foiling, as the ones catching the mast will stop you foiling these days, a lot earlier than "wing weed".

But back to the topic - we control with our weight distribution on a foil, and we have our COG high above the COE of the lifting wing which dampens the torque, thus possible to ride a non stable wing - really amazing actually.
Also the reason there is a limit probably, to how performant high AR lifting wings you can ride stabless, but depends on skill most likely.

So the fact that you CAN a foil stabless even with a negative pitching effect profile/wing, is true, and quite different from gliders and aircraft IMO :D

8) Peter

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Re: Why a stabi, when wing foiling?

Postby joekitetime » Thu Dec 03, 2020 8:02 pm

Thanks for the comments. I kept dreaming about trying it on kite foiling but never did. Now that I'm riding FONEs setup it is very easy to not attach the stab so I'm gonna force myself to give it a whirl winging.

I'll report back as well!

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Re: Why a stabi, when wing foiling?

Postby Dontsink » Thu Dec 03, 2020 11:20 pm

IMHO the future of foiling is not stabless or more high aspect...it is this:



Half the wingspan,more maneuvrable, a hundred times safer, automatic breach control,stronger structure, infinity wing design has very interesting possibilities in reducing wingtip vortices so efficiency might be brilliant...this design solves so many issues in standard foil models.

You could design the stab as an infinity wing too,so the foil would not be a sword&dagger bearing psycho out to get ya, or stagger the main foil wings and go stabless with some stability.

Bruce is now working with the fastest IKA foil designer.
Hope it comes to market soon at a reasonable price :)

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Re: Why a stabi, when wing foiling?

Postby fluidity » Fri Dec 04, 2020 7:49 am

Dontsink wrote:
Thu Dec 03, 2020 11:20 pm
IMHO the future of foiling is not stabless or more high aspect...it is this:



Half the wingspan,more maneuvrable, a hundred times safer, automatic breach control,stronger structure, infinity wing design has very interesting possibilities in reducing wingtip vortices so efficiency might be brilliant...this design solves so many issues in standard foil models.

You could design the stab as an infinity wing too,so the foil would not be a sword&dagger bearing psycho out to get ya, or stagger the main foil wings and go stabless with some stability.

Bruce is now working with the fastest IKA foil designer.
Hope it comes to market soon at a reasonable price :)
It's extraordinarily pretty, his attention to detail on the finish is commendable.

However I think the design is a bit stink for working the limits of low stall speed which is important for winging. If I'm wrong, be prepared to see the return of biplanes like the Wright brothers pioneered.
The problem for low speed is that in the box design, like with a biplane, the top lifting surface is in the vertical shadow of the bottom wing, which is already pushing water down. So the top wing gets less lift than it would if it were running independently. The bottom wing has a downforce of water on it from the top wing so it gets less lift. The advantage is manouverability improvement from width reduction but you need to move faster to get the same lift as you would with the lifting area in one wing of the same chord but double the span. Go fast enough and the difference become less significant as the water has less time to react to the box wing. But slow- bad choice.

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Re: Why a stabi, when wing foiling?

Postby Dontsink » Fri Dec 04, 2020 9:37 am

fluidity wrote:
Fri Dec 04, 2020 7:49 am
Dontsink wrote:
Thu Dec 03, 2020 11:20 pm
IMHO the future of foiling is not stabless or more high aspect...it is this:



Half the wingspan,more maneuvrable, a hundred times safer, automatic breach control,stronger structure, infinity wing design has very interesting possibilities in reducing wingtip vortices so efficiency might be brilliant...this design solves so many issues in standard foil models.

You could design the stab as an infinity wing too,so the foil would not be a sword&dagger bearing psycho out to get ya, or stagger the main foil wings and go stabless with some stability.

Bruce is now working with the fastest IKA foil designer.
Hope it comes to market soon at a reasonable price :)
It's extraordinarily pretty, his attention to detail on the finish is commendable.

However I think the design is a bit stink for working the limits of low stall speed which is important for winging. If I'm wrong, be prepared to see the return of biplanes like the Wright brothers pioneered.
The problem for low speed is that in the box design, like with a biplane, the top lifting surface is in the vertical shadow of the bottom wing, which is already pushing water down. So the top wing gets less lift than it would if it were running independently. The bottom wing has a downforce of water on it from the top wing so it gets less lift. The advantage is manouverability improvement from width reduction but you need to move faster to get the same lift as you would with the lifting area in one wing of the same chord but double the span. Go fast enough and the difference become less significant as the water has less time to react to the box wing. But slow- bad choice.
Those are very good points, in the video it does seem to ride fine but he is kiting,not winging or surf foiling it.
Wings have very little horsepower vs kites so foil behaviour at slow speeds and how it transitions from slog to foil mode is way more critical,if this foil stalls at significantly lower AOA than a single span it might be a dead end for winging.

But i am optimistic, and just to clarify, this is not a biplane, it is an infinity or prandtl wing with closed ends...might make a huge difference.A classic biplane has 4 wingtips bleeding lift and energy ,this has none (on paper, i know :)

Pumpability is also very important in DWind and surf, i am curious as how it will behave.

But all of this is theoretical and the true answers will only come through building many protos and having rippers riding the @#€ out of them, i hope they do not focus only in the race kitefoil end but look for application in the booming wing and surf foil market.
Time will tell.

Sorry for the thread hijack,this was about stabless....

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Re: Why a stabi, when wing foiling?

Postby PrfctChaos » Fri Dec 04, 2020 10:15 am

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....

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Re: Why a stabi, when wing foiling?

Postby purdyd » Fri Dec 04, 2020 12:59 pm

So the fact that you CAN a foil stabless even with a negative pitching effect profile/wing, is true, and quite different from gliders and aircraft IMO :D
Well there are plenty of unstable aircraft in aviation, fighters.

And I am seeing a trend with stabilizers where the downward lift is decreasing from shorter fuselages, chopping, shimming, and even design.

So basically trading stability for reduced drag and maneuverability,

From a pure lift to drag standpoint I am not convinced that stabless has an advantage.

But I am not sure has anyone truly designed and optimized a foil for stabless?

Can you pump stabless?

The unicycle versus bicycle analogy is a good one.

The box wing is interesting but I wonder why it incorporates a stabilizer on the above implementation?

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Re: Why a stabi, when wing foiling?

Postby Dontsink » Fri Dec 04, 2020 2:46 pm

purdyd wrote:
Fri Dec 04, 2020 12:59 pm
So the fact that you CAN a foil stabless even with a negative pitching effect profile/wing, is true, and quite different from gliders and aircraft IMO :D
Well there are plenty of unstable aircraft in aviation, fighters.

And I am seeing a trend with stabilizers where the downward lift is decreasing from shorter fuselages, chopping, shimming, and even design.

So basically trading stability for reduced drag and maneuverability,

From a pure lift to drag standpoint I am not convinced that stabless has an advantage.

But I am not sure has anyone truly designed and optimized a foil for stabless?

Can you pump stabless?

The unicycle versus bicycle analogy is a good one.

The box wing is interesting but I wonder why it incorporates a stabilizer on the above implementation?
Unstable aircraft (notably canard config fighters) rely heavily on fly-by-wire tech,with computers constantly adjusting flight surfaces even to maintain straight and level flight,with no pilot input.Even airliners are using this "digital stability" to a lesser degree.

As for the box wing stab, it needs it because unless you stagger the wings(one further in front) significantly , the longitudinal (pitch) stability behaviour is pretty much the same as a monoplane foil setup.

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Re: Why a stabi, when wing foiling?

Postby Peter_Frank » Fri Dec 04, 2020 7:42 pm

It is interesting, the "box" wing stab, but difficult to say if it is "the" thing.

As regarding airplanes, yes double deckers, they are really agile and look good (main reason why the Pitts Special exist - and I love these, both flying and watching)

The performance as such, in terms of glide and lift is not something you want to bragg about....

And the pitch stability is the very same, as a single front wing, so no difference there.

But agree, there could be practical advantages, you dont risk getting stabbed if you drop down on you wing(s) tip.

And you might be able to make two higher aspect wings, with more structural rigidity, and more lively.

8) Peter


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