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the aspect ratio mystery

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papasmerf
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the aspect ratio mystery

Postby papasmerf » Sat Sep 05, 2020 11:38 pm

can't figure it out.

some manufacturers list the aspect ratio, some just give wing span, some give chords in some random location on the wing it seems, some just describe the wing and how it rides (according to whom it never says).

is there some sort of science behind the low/mid/high aspect wing? if so,, why don't manufacturers give an aspect ratio?

maybe it doesn't matter?

can there be a high aspect wing that is super stable? what design features or measurements of the wing determine stability and carvabilty? how do we measure carvability?

it is great to read reviews on wings but the reviews can be biased or a genuine review can be a lot different from what a beginner/intermidiate may experience due to skill level or conditions or even age.

i've talked to some great guys on here but I still can't figure out what to finally buy for my very own,,,i realize i am over analyzing,, my friend says just buy something but,,, i am in a unique situation where i have a very usable borrowed foil set up now that is working great at my still learning curve (foot switches and down loops during transitions is what i am banging my head against at the moment)

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Re: the aspect ratio mystery

Postby tkaraszewski » Sat Sep 05, 2020 11:52 pm

What’s your question? Here’s a page about wing aspect ratio if you’re interested: https://en.m.wikipedia.org/wiki/Aspect_ ... ronautics)

“Stable” is not just a function of the wing but also the stabilizer (guess where that name comes from?) and it’s distance from the wing.

There’s no hydrodynamic definition of “carvability” there’s no SI unit for carving. What do you mean when you say that?

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Re: the aspect ratio mystery

Postby PrfctChaos » Sun Sep 06, 2020 12:13 am

The goal of high aspect ratio is to reduce the drag component called "induced drag". As a rule of thumb you can expect a higher aspect foil to be lower drag. You pay with wider wingspan, again generally speaking it could take more effort to make it turn / carve with the wider wingspan. But you might call this good roll stability, someone else might call it unresponsive or difficult to carve. Personal preferance.

Smaller stab, shorter fuse, etc can all be played with to change some of the handling.

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Re: the aspect ratio mystery

Postby tegirinenashi » Sun Sep 06, 2020 1:15 am

PrfctChaos wrote:
Sun Sep 06, 2020 12:13 am
...it could take more effort to make it turn / carve with the wider wingspan...
Why, because of longer wing higher moment of inertia? I remind you that it is not an airplane.

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Re: the aspect ratio mystery

Postby tkaraszewski » Sun Sep 06, 2020 2:10 am

tegirinenashi wrote:
Sun Sep 06, 2020 1:15 am
PrfctChaos wrote:
Sun Sep 06, 2020 12:13 am
...it could take more effort to make it turn / carve with the wider wingspan...
Why, because of longer wing higher moment of inertia? I remind you that it is not an airplane.
Because you have less leverage against the water with a long wing than a short one. You are still turning this thing by pushing on it with your body weight, and it takes longer to move the end of a long lever arm than a short lever arm with the same force.

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Re: the aspect ratio mystery

Postby papasmerf » Sun Sep 06, 2020 3:12 am

tkaraszewski wrote:
Sun Sep 06, 2020 2:10 am
tegirinenashi wrote:
Sun Sep 06, 2020 1:15 am
PrfctChaos wrote:
Sun Sep 06, 2020 12:13 am
...it could take more effort to make it turn / carve with the wider wingspan...
Why, because of longer wing higher moment of inertia? I remind you that it is not an airplane.
Because you have less leverage against the water with a long wing than a short one. You are still turning this thing by pushing on it with your body weight, and it takes longer to move the end of a long lever arm than a short lever arm with the same force.
so then a lower aspect wing will carve faster then? or does the fuse length also come into play? is a shorter fuse more pitchy?

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Re: the aspect ratio mystery

Postby tkaraszewski » Sun Sep 06, 2020 3:56 am

papasmerf wrote:
Sun Sep 06, 2020 3:12 am
tkaraszewski wrote:
Sun Sep 06, 2020 2:10 am
tegirinenashi wrote:
Sun Sep 06, 2020 1:15 am


Why, because of longer wing higher moment of inertia? I remind you that it is not an airplane.
Because you have less leverage against the water with a long wing than a short one. You are still turning this thing by pushing on it with your body weight, and it takes longer to move the end of a long lever arm than a short lever arm with the same force.
so then a lower aspect wing will carve faster then? or does the fuse length also come into play? is a shorter fuse more pitchy?
Longer wingspans resist roll, bigger stabilizers and longer fuselage resist pitch. It’s hard to relate this directly to “carvy”, tough. Carving isn’t just the ability to turn quickly. You can slide down a snowy hill on an inflatable sled doing 360s rotating a lot faster than you could carve down the hill on skis, but the that doesn’t make the sled “carvier” than the skis.

Similarly, I’d say that when I watch guys riding monofoils, they turn quickly, but they slide more than they carve. Some might call that “skatey”.

So when you discuss carving, it helps to know if you’re talking about turning rate or a locked-in edge feeling, or a combination of the two, or something else.
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Re: the aspect ratio mystery

Postby Peter_Frank » Sun Sep 06, 2020 8:27 am

One can not simplify things like that :-?

Aspect ratio is only one out of a huge number of factors.

Fuselage length, stab size, stab tips and di/anhedral, position of mast to wing, wing area, wing dihedral, wing sweep, wing taper, wing camber line, wing thickness, wing LE diameter, wing washout, wing profile change towards the tips, and the list could go on and on.

Everything is connected, and you also can not "add" the individual elements, in order to say how a hydrofoil will work, as it also has to stay balanced, and feel right.

tkaraszewski has correctly written about the typical characteristics of different aspect ratios.

So in short, higher aspect ratio turn slow (feels slower as they initiate turns slower) but has less drag in particular when going upwind meaning high lift, and lower aspect ratio wings turns fast and are a lot more forgiving and easy, they almost dont stall.

But how "Carvey" a wing is, got nothing to do with how fast it feels and turns - especially because skatey and carvey is usually seen as too opposite characteristics, but some see them as the same :wink:

We like to believe we can use the numbers we can read, as the "truth" about how a hydrofoil will work.
But they can only be taken as a rough thumbrule, and nothing but that :D

8) Peter

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Re: the aspect ratio mystery

Postby Iridian » Sun Sep 06, 2020 7:35 pm

I think carve is the ability to turn narrowly without stalling the wing..

Higher aspect wings will be harder to turn because of increased leverage, but they'll also stall significantly easier. The lower the aspect ratio, the harder induce flow separation, thus generating a stall.

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Re: the aspect ratio mystery

Postby tegirinenashi » Sun Sep 06, 2020 8:25 pm

The stall speed is defined mostly by the wing area. This is why airplanes use flaps to extend it.

I agree that higher aspect ratio wings are more roll resistant. By how much?

Consider laying high aspect wing over low aspect, say Moses 800
https://moseshydrofoil.com/products/win ... -race-wind
over LF Rocket. Both wings are about 850 cm^2, but the high AR Moses wing extends little over 10 cm at each side. Now, I'm guess estimating the average chord at the wing tips to 5 cm. Which would give you additional leverage of 100 cm^2, at the arm of about 35 cm, which is 3500 cm^3. This is the top estimate, and the real number should be less because at lesser arm leverages the low AR wing has more area to contribute.

Keep in mind that it is not only the wing that contributes to roll stability. Mast too. Assuming a 90 cm mast with 12 cm chord, submerged in half it would give you the leverage 90/2*12*45/2 = 12150 cm^3. Add to this the roll stability due to the wing (850 cm^2 area * 20 cm average arm = 17000 cm^3), and you'll arrive to the roll stability difference between high and low AR wings of perhaps 10%.


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