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comparing wing lift

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slowboat
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comparing wing lift

Postby slowboat » Thu Jun 27, 2019 12:40 am

There are many factors influencing the lift of a front wing but if you ONLY used surface area/aspect ratio is there an easy was to compare wings? For example, which of the following would have more lift?

Wing #1: 1530 cm2/ AR 4.3

Wing #2: 1340 cm2/ AR 5.2

Thanks for your input

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Re: comparing wing lift

Postby grigorib » Thu Jun 27, 2019 12:52 am

I think you should consider profile thickness as second major factor after the surface area, not the AR.

Both of above wings are overly large for kitefoiling unless you're a heavy guy. The largest wing will likely have better lowend and worse high end. The 1340 sq.cm. is also big and I think it would handle lowend to the point you won't be able to differentiate from the larger wing.

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Re: comparing wing lift

Postby tkaraszewski » Thu Jun 27, 2019 6:41 am

All else being equal, bigger wings make more lift at a given speed. Smaller wings have to go faster to make the same amount of lift. This is why some small aircraft use clipped wings to go faster. The plane weighs about the same with the smaller wing, so needs to create the same amount of lift for level flight, but with the smaller wing, does so at a higher speed.

Aspect ratio does not factor greatly into total lift created. The advantage of high aspect ratio wings is that for a given wing area, you get the same amount of lift, but with less drag than a lower aspect ratio wing. This comes at the cost of maneuverability and low-speed performance (high aspect ratio wings stall more easily).
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Peter_Frank
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Re: comparing wing lift

Postby Peter_Frank » Thu Jun 27, 2019 7:38 am

On my mobile right now, but some rough calculations based on how loss of lift increase in drag is estimated/calculated on really low AR wings, tells me the 14% smaller wing will still have the same or more "lift" (or sink rate which is time you can glide without power/kite, as the ability to ride in low wind with the same amount of power is depending on drag also).

Maybe not much difference between the stated wings though.

The low AR big wing will be easier to ride, and have a gentler more forgiving stall.
Can be pushed to almost a dead stop, without stalling.
Less pitch sensitive.

But the small one, besides the same, will have quite a better upwind angle, which can be the determining factor in marginal winds.
Able to ride faster, and still same low end.
Span only 3% different so the small area one would probably turn just as fast and feel more nimble.

Also feel more "rigid" though, which some like others don't.

Everything else being equal regarding profile, as you asked :D

My estimations at least.

8) Peter
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slowboat
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Re: comparing wing lift

Postby slowboat » Fri Jul 12, 2019 8:04 am

Peter, can you explain what you mean by more “nimble” and more “rigid” for the higher AR wing?

“More nimble” meaning acceleration and declaration?

“More rigid” meaning harder to turn? Roll and yaw?

Thanks

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Re: comparing wing lift

Postby nixmatters » Fri Jul 12, 2019 8:59 am

Anyone tried measuring the towing load behind a boat or cable?
A load cell at the boat end of the rope or at the handle end at the cable park should produce comparable lift/drag data at different speeds.
Only issue I see is that different rider weight, water/air density and wind would lead to relative rather than absolute test results.

Any thoughts on this?

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Re: comparing wing lift

Postby Foil » Fri Jul 12, 2019 9:44 am

nixmatters wrote:
Fri Jul 12, 2019 8:59 am
Anyone tried measuring the towing load behind a boat or cable?
A load cell at the boat end of the rope or at the handle end at the cable park should produce comparable lift/drag data at different speeds.
Only issue I see is that different rider weight, water/air density and wind would lead to relative rather than absolute test results.

Any thoughts on this?
Easy and cheap to set up using this mini crane scale which goes up to 500kg.
It's what I use to test lines and knots.
ImageURL=https://www.directupload.net]Image[/URL]

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Re: comparing wing lift

Postby nixmatters » Sun Jul 14, 2019 4:37 pm

Foil wrote:
Fri Jul 12, 2019 9:44 am
nixmatters wrote:
Fri Jul 12, 2019 8:59 am
Anyone tried measuring the towing load behind a boat or cable?
A load cell at the boat end of the rope or at the handle end at the cable park should produce comparable lift/drag data at different speeds.
Only issue I see is that different rider weight, water/air density and wind would lead to relative rather than absolute test results.

Any thoughts on this?
Easy and cheap to set up using this mini crane scale which goes up to 500kg.
It's what I use to test lines and knots.
Easy and cheap for sure, but far from light weight and waterproof.
Have you come across something more compact? And upto 50kg should suffice for measuring foiling loads?

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Re: comparing wing lift

Postby Europ2 » Mon Jul 15, 2019 12:59 am

nixmatters wrote:
Fri Jul 12, 2019 8:59 am
Anyone tried measuring the towing load behind a boat or cable?
Any thoughts on this?
Today, DiY efoils allow to test wing efficiency easily without taking into account the influence of the kite or the wind direction or the rider skill, or....
At identical speeds( 10, 20, 30 kmph), the only question is which front wing will draw less amp (=less drag) ?

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Re: comparing wing lift

Postby tkaraszewski » Mon Jul 15, 2019 6:02 pm

The scale and efoil power consumption are interesting solutions here. They hit on a fact that hasn't really been talked about in this thread:

All wings make the exact same amount of lift. They lift the weight of the board + the rider - the weight supported by the kite. If they lift more than this, they will fly up to the surface and breach, if they lift less than this, then you're not foiling.

Learning to foil is largely about learning to control the lift that your wing makes by controlling it's angle of attack in the water. And wings will generate more lift with more speed, so you need to adjust the angle of attack so that they generate less lift, and the total amount of lift stays the same.

What is interesting is the amount of drag a given wing generates at a given speed, and the lowest speeds for which a given wing will generate enough lift to foil.
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