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### Calculating Aspect Ratios

Posted: Fri Jan 11, 2013 3:52 am
Does anyone here know how to calculate the aspect ratio of a kite? Or do you simply measure the flatness of the arc and divide by what exactly?

I see kite manufacturers who list their aspect ratios at 5.0, 5.5, etc but I am curious to know how they arrive at this calculation.

### Re: Calculating Aspect Ratios

Posted: Fri Jan 11, 2013 4:15 am
Aspect ratio = ((wing span)^2/surface area)
So a hypothetical 12m kite shaped like a flat rectangle when unrolled, with a 5.4 AR has a span of 9.2m and chord of 1.3m.
Really kites aren't shaped so simply, and other factors are considered but that's the idea.

### Re: Calculating Aspect Ratios

Posted: Fri Jan 11, 2013 4:26 am
I was thinking more simple in that you could take the average length of the struts and divide that into the length of the leading edge. If it was a perfect rectangle you could divide the length by the width I guess.

One number is as good at another... that is if all the manufacturers have there own unique way to calculate it... which wouldn't surprise me

### Re: Calculating Aspect Ratios

Posted: Fri Jan 11, 2013 4:27 am
BWD wrote:Aspect ratio = ((wing span)^2/surface area)
So a hypothetical 12m kite shaped like a flat rectangle when unrolled, with a 5.4 AR has a span of 9.2m and chord of 1.3m.
Really kites aren't shaped so simply, and other factors are considered but that's the idea.
Ok...so how do you calculate the surface area of an irregular shape such as a kite? I can't evenly divide it into two triangles (for the wing tips) and a rectangle (for the middle).

I want to measure my kite and determine the aspect ratio is what I am getting at.

Thanks.

### Re: Calculating Aspect Ratios

Posted: Fri Jan 11, 2013 5:09 am
needs more triangles,
that's how the machines do it,
also the men,
usually.

### Re: Calculating Aspect Ratios

Posted: Fri Jan 11, 2013 5:16 am
BWD is correct. Here is an example of some different shapes all having the same AR.
Cheers!

### Re: Calculating Aspect Ratios

Posted: Fri Jan 11, 2013 6:17 am
Kiteus Maximus wrote:
BWD wrote:Aspect ratio = ((wing span)^2/surface area)
So a hypothetical 12m kite shaped like a flat rectangle when unrolled, with a 5.4 AR has a span of 9.2m and chord of 1.3m.
Really kites aren't shaped so simply, and other factors are considered but that's the idea.
Ok...so how do you calculate the surface area of an irregular shape such as a kite? I can't evenly divide it into two triangles (for the wing tips) and a rectangle (for the middle).

I want to measure my kite and determine the aspect ratio is what I am getting at.

Thanks.
If you have a 12m kite for example then wouldn't the surface area of the kite be 12m**2 ?
I always assumed that was the case but maybe that number is a measure of something else.

If it was me I would just measure the area between each strut (on one side) and add them up and double the number... won't be perfect rectangles but probably close enough.

My c-kites are less curvy than a typical SLE I think... 5 struts, one middle and two on each side which breaks the kite into 3 sections per side... and those sections are pretty rectangular... should be a pretty good approximation.

### Re: Calculating Aspect Ratios

Posted: Fri Jan 11, 2013 7:25 am
Kiteus Maximus wrote: Ok...so how do you calculate the surface area of an irregular shape such as a kite? I can't evenly divide it into two triangles (for the wing tips) and a rectangle (for the middle).

I want to measure my kite and determine the aspect ratio is what I am getting at.
frankm1960 wrote: If you have a 12m kite for example then wouldn't the surface area of the kite be 12m**2 ?
I always assumed that was the case but maybe that number is a measure of something else.
Yes, first you need to measure your actual kite size. Meter-number printed on the kite is just marketing.

If you are Android enlightened, you can use this app with A4 or letter paper to give reference on the plane you are measuring. I guess there could be similar programs for other platforms.

As then you have the kite size on the software you can have also other measures of the kite.

This example pic has credit card as measurement plane size reference.
unnamed.jpg (41.88 KiB) Viewed 2269 times

### Re: Calculating Aspect Ratios

Posted: Fri Jan 11, 2013 4:31 pm
Hansen Aerosports wrote:BWD is correct. Here is an example of some different shapes all having the same AR.
Cheers!
...
And everyone of those shapes would have a different AR based on what the
actual span is After adding in the curve the bridals put in the shape.

Laying a kite flat on the ground is kinda meaningless in relation to the actual
projected span, because the kite doesn't fly Flat like my hang glider. Actually
the tips of a typical kite aren't pulling hardly -0- in relation to the center
of the kite.

Look at the AR on a Revolution-II and it's projected aria is the same as
the aria when it's flat on the ground, (like my Rigid-wing HG) ; so all
the kite is pulling.

*** So Ya Must measure the span from tip to tip "After" the bridals put the
arc in the kite for the AR to accurate.

And This is where i enjoy saying that kites that we use are a FAR cry
from where they could be based on available aerodynamics of today.
My Rigid wing has 158 sq/ft of aria when flat and 158 ft projected, because
ALL of the wing is pulling. 158sq/ft = 14.69 M and it can Easily go
forward at close to 80mph; a 14.6M water kite would be Lucky to ever
see anything much over 30mph because the airfoils SUCK in comparison
to what i fly on a HG !!

Bille

### Re: Calculating Aspect Ratios

Posted: Fri Jan 11, 2013 11:36 pm
[quote]Ok...so how do you calculate the surface area of an irregular shape such as a kite? I can't evenly divide it into two triangles (for the wing tips) and a rectangle (for the middle0[quote]

Yeah there is probably some app now a days to do this, but if you want to do it old school it is not that hard.

1) Get your builders square, a tape measure, and some string.
2) Go out into the back yard and create an X,Y axis with your string and some stakes to hold the string
3) Lay your kite down at the vertex of the X, Y axis
4) Now measure some points on your kites perimeter. Measure the X, and Y.
example: Point A is 6 inches out and 5 inches up. (6,5)
5) The more points the more accurate
6) Get a piece of graph paper and come up with a conversion to use. Example: 1 square equals 1 inch.
7) Plot all your points. Example: point A would be 6 grids in, by 5 grids up
8 ) If you have a drawing curve use that to help connect the dots
9) count all full squares. Those squares completely inside your diagram
10) For the split squares you can be lazy and multiply the total split squares by .5. or it is better to estimate each one. Example: first square is about .25 enclosed, the next is .5 enclosed, the next is .9 enclosed. Sum these up and add to the number found in 9