how much force is involved in kiting?

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how much force is involved in kiting?

Postby go4kitesurfing » Mon May 27, 2013 3:25 pm

windstoked wrote:Someone should develop a system with tensiometers that can give precise information on forces on the lines and chicken loop. It could have it's own computer to store the data, and even include gps data on speed and height attained. This would make accurate comparison of kites more scientific.
They could also be incorporated into footstraps to compare both impact and shear forces experienced between boards.
Maybe someone is already using these in R and D?


I looked into this quite a while ago. Very interesting and possible but it gets expensive pretty quickly if you want reliable data and it's hard to find a reasonable safe way to recover the cost. I talked to manufacturers and designers back then and they were definitely interested in the results but not willing to invest.
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Re: how much force is involved in kiting?

Postby PistolPete » Mon May 27, 2013 6:32 pm

:ugeek:

Image


Image


The two graphs (sheeted-in & sheeted-out) illustrating the pulling force of a kite in varying airspeeds. This is based on simple calculations using the lift coefficient equation and is intended to show a few conceptual relationships only. Estimations/ Inaccuracies include:
- Kite is not an ideal foil-bearing body
- Kite planform area is not uniform
- Kite chord varies and is flexible
- Inefficiencies unaccounted for
- Lift Coefficient values vary
- Air Density values vary
- And many more…

The illustrations have a color overlay indicating a notional limited usable range. There are calculated curves for 5, 10, and 15 square meter planform/projected area kites. This is different than the typical windrange-vs-kite size correlations. Hopefully this helps to visualize the magnitude of force at various airspeeds, using different size kites. What is not included is the direction of the force (vector), which helps determine how useable the force will be.

Airspeed is calculated as a function of force in the illustrations. Beach windspeed (true wind velocity) is easy to visualize with a steady kite as it is equal to the kite airspeed (apparent wind velocity). As soon as the kite moves, the apparent wind velocity changes. The kite can be moved by steering (sine-ing) and/or being set in motion from sailing. Y-axis airspeed can be visualized using three different perspectives:
(1) As beach/true wind velocity (for forces seen static flying)
(2) As kite/apparent wind velocity (for total forces seen at the kite)
(3) As sailing and/or sin-ing wind velocities (for forces the rider controls)

One of the graphs illustrates the minimum calculated forces for a kite sheeted-out (using CL=0.75) and the other graph illustrates the maximum calculated forces for a kite sheeted-in (using CL=1.7). The two graphs show different usable kite windranges depending on the sheeting of the kite. Again the specific graph numbers may not be accurate to actual kite performance but, this does provide a general idea of the range a depower kite could provide. Many other pro/con variables influence actual airspeed-vs-force curves. Kite shape, rigidity, weight, line lengths, etc… are ignored for mathematical simplicity. The above concepts are all well known, but sometime drawing a picture helps.

Ref:
http://en.wikipedia.org/wiki/Lift_coefficient
http://en.wikipedia.org/wiki/Air_density
http://en.wikipedia.org/wiki/Planform
http://en.wikipedia.org/wiki/Wind_triangle
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Re: how much force is involved in kiting?

Postby knyfe » Tue May 28, 2013 10:01 pm

i am actually committed to make such a thing. The easy way would be if we use a laptop - well watertight and just use some LAbView and NI stuff to get it going. I assume no one would go for that which would also be a hassle with a backpack and everything.

So I already found a $50 data logger which streams straight to a SD card. I want to stream/log 4 force transducer at about 100Hz which should give me plenty of resolution compared with the speeds involved.

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Re: how much force is involved in kiting?

Postby buckidge » Tue May 28, 2013 10:31 pm

knyfe wrote:i am actually committed to make such a thing. The easy way would be if we use a laptop - well watertight and just use some LAbView and NI stuff to get it going. I assume no one would go for that which would also be a hassle with a backpack and everything.

So I already found a $50 data logger which streams straight to a SD card. I want to stream/log 4 force transducer at about 100Hz which should give me plenty of resolution compared with the speeds involved.

G


What's the $50 logger with SD card? I'd like to have my hands on that for work!
Portable/customizable logger... sounds like Arduino might have been my approach before going to expensive NI hardware!
If this really does take off and you need any help, let me know. I'd like to think I could contribute. Logging 4 transducers doesn't seem too tricky..
"A ship is safe in harbor, but that's not what ships are built for"
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Re: how much force is involved in kiting?

Postby knyfe » Wed May 29, 2013 12:22 pm

Well, I start with

https://www.sparkfun.com/products/10216

and go from there. Once I have the logging established it should be a blizz to get the transducers sorted out. Actually not too big of a project from my perspective as well. Thats why I started to buy parts.

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Re: how much force is involved in kiting?

Postby PistolPete » Thu May 30, 2013 9:37 pm

Knyfe – Nyce project!
Please share the data with us.

:text-tmi:

Temperature
Attached is a temperature plot for the 10m planform area wing. The blue (lower=less wind needed for pull) lines are for air density for very cold dry air (23°F or -5°C = 1.13Kg/m³ @ Sea Level) and the red (upper=more wind needed for pull) line represents very hot dry air (105°F or 40.5°C = 1.32Kg/m³ @ Sea Level). The biggest difference is on the Sheeted-Out plot because lift efficiency is low so, more wind is needed to make up the difference in air density. Some numbers are:
50lbs of pull sheeted-out needs 1.7mph more wind for hot air (sheeted-in needs 0.8mph).
100lbs of pull sheeted-out needs 2.4mph more wind for hot air (sheeted-in needs 1.1mph).
150lbs of pull sheeted-out needs 2.9mph more wind for hot air (sheeted-in needs 1.4mph).
200lbs of pull sheeted-out needs 3.4mph more wind for hot air (sheeted-in needs 1.6mph).
250lbs of pull sheeted-out needs 3.8mph more wind for hot air (sheeted-in needs 1.8mph).
Image

Altitude
Attached is an altitude plot for the 10m planform area wing. The green (lower) lines are for air density for sea level dry air (1.2Kg/m³ @68°F/20°C) and the purple (upper) line represents dry mountain air at 10,000ft/3048m (0.826Kg/m³ @ 68°F/20°C). To show only the altitude differences, the temperatures are held same but, note that would be a warm day that far up a mountain. Some numbers are:
50lbs of pull sheeted-out needs 2.6mph more wind for mountain air (sheeted-in needs 2.1mph).
100lbs of pull sheeted-out needs 3.7mph more wind for mountain air (sheeted-in needs 3.0mph).
150lbs of pull sheeted-out needs 4.5mph more wind for mountain air (sheeted-in needs 3.7mph).
200lbs of pull sheeted-out needs 5.2mph more wind for mountain air (sheeted-in needs 4.2mph).
250lbs of pull sheeted-out needs 5.9mph more wind for mountain air (sheeted-in needs 4.8mph).
Image

Humidity
No plots needed for this one. Even for worst case (high temperature) Air Density only varies 0.3% between the full range of 0% and 100% humidity. Dryer air is denser (better for lift) than humid air, because water has less molecular mass than air. If it is raining, your kite will get heavier, and you will lose pull, otherwise humidity is really a non-factor.

Wind Gusts
Attached is a plot for gusts-vs-pull assuming 68°F/20°C dry sea level air at 60lbs of steady lift (17mph wind sheeted-out or 11.5mph sheeted-in). For simplicity it is assumed the wind gusts are in the same direction as the apparent wind seen by the kite (worst case). Actual gusts are generally in the true wind direction. The brown (upper) line represents when sheeted-out what gust speeds cause what additional pull. The pink (lower) line represents when sheeted-in what gust speeds cause what additional pull. This plot shows why it can be much more challenging to kite in gusty conditions. And, the lulls that accompany gusts add even more to the challenge (by reducing pull). This plot also illustrates that the effects of gusts/lulls are quite a bit more pronounced when sheeted-in. Some numbers are:
Sheeted-In
4mph gusts while sheeted-in sailing in 17mph winds adds 50lbs of pull
7mph gusts while sheeted-in sailing in 17mph winds adds 100lbs of pull
10mph gusts while sheeted-in sailing in 17mph winds adds 150lbs of pull
12mph gusts while sheeted-in sailing in 17mph winds adds 200lbs of pull
Sheeted-Out
6mph gusts while sheeted-in sailing in 17mph winds adds 50lbs of pull
11mph gusts while sheeted-in sailing in 17mph winds adds 100lbs of pull
15mph gusts while sheeted-in sailing in 17mph winds adds 150lbs of pull
19mph gusts while sheeted-in sailing in 17mph winds adds 200lbs of pull
Image
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Re: how much force is involved in kiting?

Postby turbinedude » Thu May 30, 2013 11:01 pm

Whow,
Pistol Pete - that's an impressive graph.
Did you make that?
Does anyone want to buy Augmentor Shades with force dial holographic projections?
Get real time force readings display on the inside of glasses.
Along with air speed and board speed?
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Re: how much force is involved in kiting?

Postby gtilde » Thu May 30, 2013 11:31 pm

Wow. And I wascthinking that some high speed framesets with a kiter popping/doing some airs perpendicular to camera to estimate quasi instantaneous velocities (w/interpolations of course) would be adequate to generate some decent estimate of maximum gross forces in 2 dimensions...
you guys are heavy-duty!
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Re: how much force is involved in kiting?

Postby gtilde » Thu May 30, 2013 11:31 pm

Duplicate post
Last edited by gtilde on Fri May 31, 2013 7:51 am, edited 1 time in total.
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Re: how much force is involved in kiting?

Postby cliftoncutshall » Fri May 31, 2013 6:45 am

I should have paid attention in math class
was thinking about waves ](*,)
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