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Calculating Aspect Ratios

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ice
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Re: Calculating Aspect Ratios

Postby ice » Sat Jan 12, 2013 1:15 am

From wikipedia

In aerodynamics, the aspect ratio of a wing is essentially the ratio of its length to its breadth (chord). A high aspect ratio indicates long, narrow wings, whereas a low aspect ratio indicates short, stubby wings.

For most wings the length of the chord is not a constant but varies along the wing, so the aspect ratio AR is defined as the square of the wingspan divided by the area S of the wing. [which is equal to the length-to-breadth ratio for a constant chord wing.


Aspect Ratio's calculations for wings have been around for a while so all Kite companies should be calculating the same way.

For Example a 6m x 3m rectangle has a aspect ratio of 2. The length is 2 times the width.

By formula = (6^2 )/ (6x3) = 36 / 18 = 2.

The denominator in kite terms is the size of the kite (square metreage of the kite, measured accurately).

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Re: Calculating Aspect Ratios

Postby Peter_Frank » Sat Jan 12, 2013 2:32 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.


Formula is correct, and the easy way to measure (but numbers are not...)

Aspect Ratio = span / average width.

Area = span * average width.

Meaning AR = span^2 / area.

So your 12m2 kite with an AR of 5.4 has a span = sqrt(AR*area) = sqrt(5.4*12m2) = 8.0 meter.

And an average width = span / AR = area / span = 1.49 meter.


I dont agree that "numbers" are just marketing, so you simply lay your kite out flat on the ground and measure the span from tip to tip, and use the nominal size printed on the kite to calculate the AR.

That works fine - and most kites are relatively okay in their size measurement, is my experience.

Even if a 12m2 kite actually was 13m2 - the error in AR calculation will only be about 7 to 8% which is not bad really :rollgrin:


Of course, like others point out - the AR is only one parameter, as whether the area is in the middle or the tips, and how flat/c the kite is, means much more.

But for those interested in this number, using the written area and the measured span is fine IMO :thumb:

Agree that it is also interesting to measure a kite up precisely yourself, if you want to know the exact size.


Why do so many use the term "12m" about a 12m2 kite ?

The word constellation 12m does not exist as an area measurement in Danish nor German, and also lacking in most other languages, so why do so many english speaking say "12m" ?
Simple lazyness, or old bad habits or ?

:D Peter

BWD
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Re: Calculating Aspect Ratios

Postby BWD » Sat Jan 12, 2013 2:38 am

thank you peter,
me and exel...
btw
if doing it by hand, easier to fold in half and multiply by 2.
No math errors there I hope ;)

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Re: Calculating Aspect Ratios

Postby flyingweasel » Sat Jan 12, 2013 5:06 am

I reckon the easiest way to get a reasonable ball park figure and take into account archform curvature will be with a camera and scaled.

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Re: Calculating Aspect Ratios

Postby plummet » Sat Jan 12, 2013 10:40 am

it would interesting to know the changes in projected AR for different kite styles.

for example the projected ar of a C kite should be alot less than the project ar or an sle with the same AR......

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Re: Calculating Aspect Ratios

Postby Hansen Design » Sat Jan 12, 2013 8:08 pm

Hi Plummet :thumb:
Switch Kite Specifications.jpg

plummet wrote:it would interesting to know the changes in projected AR for different kite styles.
for example the projected ar of a C kite should be alot less than the project ar or an sle with the same AR......

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Re: Calculating Aspect Ratios

Postby plummet » Sat Jan 12, 2013 11:44 pm

Hansen Aerosports wrote:Hi Plummet :thumb:
Switch Kite Specifications.jpg

plummet wrote:it would interesting to know the changes in projected AR for different kite styles.
for example the projected ar of a C kite should be alot less than the project ar or an sle with the same AR......


interesting. its bizarr that the switch wave kite has the highest projected a/r. i would have thought the wave kit would have the lowest....

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Re: Calculating Aspect Ratios

Postby Hansen Design » Sun Jan 13, 2013 7:43 am

The Method is the least 'C' shaped or the models listed resulting in a higher projected span. In the realm of contemporary inflato traction kites, AR (projected or flat,) is not really a true predictor of performance unless all other variables are the same.
plummet wrote:interesting. its bizarr that the switch wave kite has the highest projected a/r. i would have thought the wave kit would have the lowest....

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Re: Calculating Aspect Ratios

Postby Kiteus Maximus » Mon Jan 14, 2013 10:07 pm

Peter_Frank 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.


Formula is correct, and the easy way to measure (but numbers are not...)

Aspect Ratio = span / average width.

Area = span * average width.

Meaning AR = span^2 / area.

So your 12m2 kite with an AR of 5.4 has a span = sqrt(AR*area) = sqrt(5.4*12m2) = 8.0 meter.

And an average width = span / AR = area / span = 1.49 meter.


I dont agree that "numbers" are just marketing, so you simply lay your kite out flat on the ground and measure the span from tip to tip, and use the nominal size printed on the kite to calculate the AR.

That works fine - and most kites are relatively okay in their size measurement, is my experience.

Even if a 12m2 kite actually was 13m2 - the error in AR calculation will only be about 7 to 8% which is not bad really :rollgrin:


Of course, like others point out - the AR is only one parameter, as whether the area is in the middle or the tips, and how flat/c the kite is, means much more.

But for those interested in this number, using the written area and the measured span is fine IMO :thumb:

Agree that it is also interesting to measure a kite up precisely yourself, if you want to know the exact size.


Why do so many use the term "12m" about a 12m2 kite ?

The word constellation 12m does not exist as an area measurement in Danish nor German, and also lacking in most other languages, so why do so many english speaking say "12m" ?
Simple lazyness, or old bad habits or ?

:D Peter


This is not a true way to calculate the aspect ratio. You can have the same aspect ratio for different sized kites and if you use your calculation logic then different size kites will have different aspect ratios.

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Re: Calculating Aspect Ratios

Postby dyyylan » Mon Jan 14, 2013 10:17 pm

Peter_Frank wrote:Why do so many use the term "12m" about a 12m2 kite ?

The word constellation 12m does not exist as an area measurement in Danish nor German, and also lacking in most other languages, so why do so many english speaking say "12m" ?
Simple lazyness, or old bad habits or ?



Because there is no such thing as "12m2", it is 12m², but most keyboards do not have a way to produce that character. Everyone know what you're talking about when you say you have a 12m kite.


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