A standard test protocol for comparing kites

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charlie
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Post by charlie » Thu Oct 13, 2005 4:11 pm

i dont get the tea bag thing,sombody thinks i was taebagging..?
himm.maybe?
you never know when you let go ...of the bar.

i rode that rapture all year, its very hard to get overpowerd on it!
no tea bagging.
so back to the task,
the mag didnt give us wind speeds and riders wight right up front
like
a 200 lbs man
with a 135x44 board
in 8 to 12 mph
on xxx kite size xxx
stayed upwind or not.
charlie

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Post by Guest » Thu Oct 13, 2005 6:05 pm

here are some stats i would find useful to compare for kites if we had a wind tunnel these would all be possible(most require a constant wind speed, or atleast a known windspeed so we can factor out that variable). I have also proposed tests for some.

1. minimum windspeed required to fly
2. bar pressure, can be measured by placing a weight at the end of a consistent length bar(with constant line lengths), and measuring the time it takes to do a kiteloop, at certain windspeed, therefore would be a measure of bar pressure/kite reaction measurement. Would have to do this with a consistent line tension or multiple tests at different tensions.
3. static pull at zenith at 20mph(powered vs depowered)
4. speed through the window(maximum bar pressure and do a kiteloop)- also can measure force generated possibly to get another reading. might have to repeat this for multi tensions or set tension constant. We can also theoretically get a maximum power reading from this?
5. projected area
6. Distortion resistance?(this one is possibly windspeed indp). We can take weights to the middle of the kite pumped at a constant pressure, and measure vs weight placed on top(imagine the kite standing on its tips), and see how rigid the leading edge is in the vertical direction. we can also do this from the horizontal direction(pinching tips together)- possibly laying the kite on its side and placing weights on its tips(ofcourse this would greatly differ with kite size.
7.Lift rating, at set wind speed jump the kite many different ways and see what the maximum force is in the vertical direction AND it's decay vs time(hangtime) - this would be the 0-60 test for kites.

If there WAS a way to keep wind speeds constant, i would definitely organize kites by projected area, and test them at "typical" wind speeds.
i.e. i would do most of the tests of a 20meter at 10mph, and for a 12m kite i would do tests at like 18 or 20mph.

it's all based on windspeed =(. If we could somehow keep it constant there are SO many tests i would love to do.

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charlie
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Post by charlie » Thu Oct 13, 2005 6:44 pm

windspeed and rider wight.
and then what z said
"skill and abletea facter...?"
and leo wind hornys xbow is like 14m sq projected at ....12m...?
your 16m BaD AsseD OCTANE 16m fly N mach is projected at what 12m..?

let it fly.
charlie

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lmontejo
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Post by lmontejo » Thu Oct 13, 2005 6:53 pm

A simple and inexpensive way to test the kites, without the use of a windtunnel, is to set up a test platform on a pickup truck, or a trailer towed behind a van.

The van or truck is taken, say to the old Navy runway in Oakland, early in the morning when the wind is zero.

The van or truck is accelerated to the different speeds that we wish to test, and the speed is confirmed by a gps. If there is no wind, after a few seconds at a given speed, we can assume that the kite is moving through the air at that speed too. Shorter lines may help. Once we have a budget, we could even run an airspeed indicator on the leading edge of the kite to confirm that our ground speed is equal to airspeed.

For each given speed that we select (say 10, 15, 20, 25, 30 mph) we run a batch of tests. I believe that "guest" (can you identify yourself?) has given us some good pointers.

Initially, because we are poor, we do not have to interface all of our meters to a computer. We simply take pictures, with a digital camera, of all our instruments, and then plot the results in a spreadsheet.

We do this for as many kites as the manufacturers are willing to provide us with.

The end result will be an unbiased comparison of the current kites in the market. As an addendum, for each kite, we can add a subjective analysis, where we can then use the terms we see in our current kiting publications (i.e. "quallity finish", "great hang-time", "awesome depower", etc.)

What would this group then achieve?

- It would allow us to participate in the future of our sport by looking and analyzing our current batch of kites in a rational way.
- It would allow us to create an association that certifies that a kite has certain metrics when compared to others.

I can imagine a future in which any kite sold would carry a sticker that would have the results of our tests.

For those of you interested in learning how a modern paraglider is tested by an independent group these, check this link: http://www.dhv.de/odb25/sourcemain/repo ... item=12034

The manufacturer (Advance) even has a link to the DHV website which is run by the independent German hang gliding and paragliding association.

It is my belief that our kiting magazines are far from this sophistication, and in fact have little interest in getting there unless pushed by the consumers.

More food for thought...

Leo

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Post by OliverG » Thu Oct 13, 2005 7:31 pm

lmontejo wrote:I am fascinated by some of the posts I am reading here.

I would like to move this discussion more to what tests people believe are useful, instead of the art vs. science dialog it has veered to. Once we decide on what makes a kite "good", we can develop metrics for that.

As for the admirers of artists here - what can I say. They must have deep pockets!

Comments?

Leo
Leo,

Great insight and comments. Personally, I'm usually interested in the science of things, what makes them work and what makes something more efficient. No doubt there is a solid foundation of science, aerodynamics, physics and structural dynamics involved in kite design. I guess in my post what I was referring to was the interpretation of it by the rider. How do you accurately quantify that? Given enough time, testers and kites it can be done to what would likely be pretty descriptive and defineable parameters and definitions, but time is a limited resource for many of us.

However, if you and others want to pursue the testing of kites, I wholeheartedly support you and we can set up a new forum for that if you want. It might be a new way of evaluating kites altogether. Keep us posted!

Ollie

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Post by OliverG » Thu Oct 13, 2005 7:34 pm

charlie wrote:i dont get the tea bag thing,sombody thinks i was taebagging..?
himm.maybe?
you never know when you let go ...of the bar.

i rode that rapture all year, its very hard to get overpowerd on it!
no tea bagging.
Leave Charlie alone - He once told me, "Hey, just 'cause i can't spell doesn't mean i don't know what's goin' on!" :rolleyes:

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Post by consumer » Thu Oct 13, 2005 8:46 pm

lmontejo wrote:.

For each given speed that we select (say 10, 15, 20, 25, 30 mph) we run a batch of tests. I believe that "guest" (can you identify yourself?)

Leo
hey Leo that was me, Kevin Kolahi, I have some ideas about what parameters i'd like to measure, but havent thought out good ways to measure them.

I think you have a good idea with the truck runs, with that and some basic tools we can make a lot of meaningful measurements.


is it only Leo and I who are willing to throw down the time and effort?

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Post by Windseeker » Fri Oct 14, 2005 10:41 am

I have to agree with the science side of the argument here. The plan a simple fact is all performance attributes of a kite can be tested, just like they have been for parachutes, paragliders and fixed wing aircraft. Just becuase we cant think of a test currently for each attribute doesn't mean it doesnt exist. Also I think the point of view of "how it feels" is garbage. "How it feels" is the culmination of all of the performance characteristics of a kite working at the same time. Not to mention we all may been looking for something different.

And while it may be nice to hear someones opinion of how a kite feels, it can truely never be an unbiased opinion. We all have certain kites we like or have been the only ones that we have ever flown. Think about it how often on this board do you ever here the comment "Well I have a full quiver of brandname X and I think they are all sh*t" Also you cant forget that there are several people who post quite frequently about about how great the performance and feel of certain kites are, but dont forget there are many of them who recieve paychecks, free gear, or discount rates and kickbacks from the very companies they are promoting.

I think it would be a nice change of pace to hear some real performance data about kites rather than the usual opinianted "I'm not biased or offiliated blah blah... but Kite X is totally better than the rest" verbal diareaha.

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Post by Guest » Fri Oct 14, 2005 10:48 am

I'm all for you guys giving this a shot. I wonder if anyone has a teenage son/daughter who would like to help and make this into a science fair project.
I like the pickup truck test too, reminds me of something I'd see on Mythbusters. Instead of a digital camera, I'd recommend using a video camera. Gps sounds good.
I can see bar pressure being a simple measurement to be made. You could rig the bar to a some sort of spring scale that could measure the load. Before doing the kiteloop/bar pressure measurement, you may want to start off with the kite at zenith.
If you guys are going to be doing this scientifically, I urge you to make at least three meaningful and reproduceable measurements so you can get the minimal amount of statistical data needed and take the average of your measurements with standard deviations too.
Even with this simple zenith bar pressure measurement, I wonder how factors such as line length would affect the bar pressure. Would you guys be willing to do tests for various line lengths to verify this doesn't affect your measurements. (Would using different lengths of bar change the bar pressure too?)
Another important thing to consider is pigtail attachment points and lengths. By changing which pigtail you attach the front/rear lines, I suspect you'll get different measurements because this changes the AoA/CoP of the kite. For e.x., the slingshot fuel has two different attachment points in the front to choose from, and three different ones in the rear. And of each of those different attachments, there are three different knots to choose from, which I suspect will give you different measurements in your bar pressure experiment (5! x 3!).
You could probably use a similar mock-up to measure a power versus depower at zenith. Just be sure to use a sheeting system with a lot of range (like ww b-SAFE) or you won't measure the full depower.
Not to be too pessimistic, but it sounds like a lot of work and gas. Of which, the final result will qualitatively agree with a "non-scientific" review as done in kiteboarder mag.
I agree that projected area is a useful tool for comparing kites. A lot of companies don't even provide the consumer with this measurement anymore. A lot of companies don't even give numerical data of the aspect ratios of their kites. Finding the projected area of windwing kites was like pulling teeth. And even still, the number given (IMO) was only an approximation. My guess, is kite designers nowadays are using programs like CAD which doesn't provide them with a way to quickly and easily measure projected area (As opposed to the home designers who can use programs like foilmaker and surfplan to design kites with a known projected area).
(and for the record the charlie tea-bagging reference was a historic reference to the pre-Rapture days...)
Art to me would be a picture capturing the stoke on each of your faces after a great day of riding...
hopefully some constructive thoughts,
bric

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Post by panzerfaust » Fri Oct 14, 2005 11:08 am

I was next to Yuri on my Rage2 12m as well :)

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