so...here's the thing....a person invented this with his/her brain...so you can at least copy it with yours....figure two things out first....does 5.5 meters mean the area of the wing or the wing span.......I would personally go for the area, being 5.5m....then put this drawing of yours on a piece of graph paper and simply do the math to figure a 5.5m2 area.....that fits around your drawing .... or just eyeball it so its darn close..say one square equals one cm...then all the math will simply answer itself....and as far as the airfoil curve is concerned...thats aerodynamic calculus....don't concern yourself too much about it IMHO.....just dont make it too flat or too scoopy.... keep it in the average....most importantly ........just make the darn thing and report back and tell us everything you learned...thats like what buggy builders do...its fun to hear about a first trial run and the like...even it it doesn't work at all.....still you may come up with a better design than the rest.......


ramble
on
DQ

Its called scaling...im doing it all the time, but you just cant scale some things.... because of the pics published on the internet arent perfectly flat or are taken with wide anfgle camera objectivos or things like that... if I had a picture, taken perfectly flat with a 50mm reflex camera lens... it would be supre easy.....

Ill do it the tough way...i already sent a aproximate plan of the sail to some guys who work repairing and building dacron and monofilm sails for yatching competition...they told me it could be done and im waiting for the price tag on it....
I checked the Argentinian website and the cheapest kitewing available is 2400 dollars...so forget about buying a real one ever... ill stick to R&D and spending some time and bux copying others people work.... No matter how much R&D it has on it... its still a piece of cloth tied to some tubes....

:D

Doing the my own math on airfoils is something I wouldn't have the slightest clue how to begin on! So agreed, a few measurements would sure help.

But eyeballing it doesn't mean that it's not going to work. Have you heard of the aqua skipper -- it's a human powered hydrofoil, and very expensive to buy, but quite possible to build:

http://www.instructables.com/id/DIY-Human-Powered-Hydrofoil-...

the guy here had basic foil information & numbers, granted --but for construction just eyeballed the foil sections, and found they worked just fine!

You've got good drawings, you'll be able to refine your numbers and foil sections with a bit of research -- surely there is some discussion of single skin foils on an obscure thread on a geeky hang - gliding forum somewhere????

But my point is, you don't have to get the foil section / curve exact for it to work, you can eyeball it with a reasonable expectation of success.

One thing is clear -- you don't give up easy! So do it the tough way, get that latin machismo up to speed to motivate you, and go for it!

Ok... no much help from users... but ill go for it any ways... im planning the fabrication, assembly of the parts in my mind...to preview possible problems on building/buying/getting something...

All the tubing will be aircraft grade aluminum... bought in an aircraft spare supplier....

The "tips" of the tubes (the ones that hold the boom and front tubes together via a rope...and the endings of the front tubes that hold the extensions in place) all will be machined with a lathe from a piece of solid delrin or similar plastic material.

The rope front linkage... just that... 10cms of fancy dacron rope full of strenght and flashy colors...

Front tubes extensions made from tent-grade-elastic-poles with some decent strenght ribbons sew on the ends....

To link the front tubes, cross tube and the boom... ill make some stainless steel braces, then ill pake 2 slots to fit it into each plastic tube ending... a bolt a cross and im done....

The boom will have a special, own design pivotal linkage so i can vary the geometriy of the wing by sliding it forward or backwards...

the battons plain antenna aluminum tubing :D

Ill kee everyone posted.... and ill upload pics as soon as i start building something....

all i got for the moment are a bunch of messy papers and the head full of unuseful ideas :D

"all I got for the moment are a bunch of messy papers and the head full of unuseful ideas"

A: a bunch of messy papers is the first step in any decent project -- i kinda think that's how the wright brothers (world's first airplane) got their start!

B: the head full of unuseful ideas -- no way, jose! I've never played with kite wings, but I don't think any of them have variable geometry in their plans! variable geometry is the future of kites, have a look at flysurfer's psycho 4, as an example...

all IMHO, of course, but I'll be following this build closely!

you may want to start a new thread with your build reports, leave the negativity of this thread behind -- just me own two cents.

I'd wish you good luck, but I think you're well on the way to making your own.

These 2 vids show that if these designs can generate pull then your design - even with any miscalculations should kick their a$$. Go for it man I'm rooting for you.

http://uk.youtube.com/watch?v=ImD8BsOITM0

http://uk.youtube.com/watch?v=hf8z4u8HTWQ

I just got one doubt.... when a kitewing sail is perfectly extended on the ground.....is it flat, or its sewed concave/convex???

Check this out... check the date... remove the "mast"

Quote:

Originally posted by xeriotti I just got one doubt.... when a kitewing sail is perfectly extended on the ground.....is it flat, or its sewed concave/convex???

It looks to me like they are sewn curved. Concave from the fliers perspective. Seems like it would catch wind better, and be more of a wing when held parallel to the ground (for lift).

You got any buddies with tube kites down there? It looked to me like the leading edge of some inflatable kites I have seen.

Its really complex, i had a lot of problems finding stuff to build the kitewings frame... but once i talked to the guy that will sew my sail... the problems duplicated instantly...hi brought lots words to my dictionary and with every word a new design problem to solve...

I suspected it was concave, but how much concave? if not constant how many stages? thru the wingspan or incresing/decreasing to the tips? this is going to drive me crazy... the frame is the easiest part now that ive noticed the basics of sail sewing...

I don't know anything about kite wings, although I've noticed a few in the sigs here on the forum. I used to race offshore, boats up to 70' and the sails were getting super high-tech!

But I do know windsurfer sails don't have much concavity in them, a lot of their curve is formed by the arc of the boom and regulated by the rope that tightens the corner furthest away from the mast. High winds = less curve, slightly depowered, the rope as tight as possible, holding the sail as tight as possible against the pressure of the wind. Low winds = more curve to maximize the power of the sail, so the rope on the corner is a bit looser, allowing the wind to push the sail out a bit so it has more curve.

The sail's deviation from the straight line is called the belly of the sail. I believe the maximum belly of the sail should be 8-14%.

For sailing, the point of maximum belly is 35-45% back from the leading edge of the sail. For windsurfing, the point of maximum belly is a little further forwards. A quick look at kitewings seems to have the maximum belly even further forwards. I reckon 25% would be too much.

The smoothness of curve in the sail is dictated by the number of individual panels. The more the panels, the higher the costs and the more precise your tolerances (less margin of error). A racing mainsail for a top-notch 60 footer will have more than 50 panels and cost more than $100,000 USD.

The point of maximum belly (in terms of how far back from the leading edge) is sewn into the sail, and is harder to change by playing with the rigging. The amount of belly (deviation from a perfectly flat plane -- the 8-14% I mention above) is a lot easier to change by playing with the rigging. The amount of belly is regulated not only by the curve sewn into the sail, but also by the tightness of the rig (dependent on the strength of the rigging -- too tight and you break the frame holding the sail), the amount of flex in the rig, amount of stretch in the sail material, and finally the amount of wind pressure you are dealing with.

In other words, you'll build / sew in about 4 % (high wind sails)-8 % (low wind sails) belly maximum, and the wind will push and stretch the sail out more, and you control that with the rigging. If your belly exceeds 12 to 16% (depending on your design) you'll start to induce more and more turbulence and drag, robbing you of available power.

The point of maximum belly back from the leading edge will be something you'll need to design into the sail, and you'll find that really hard to change after you have built your sail. The amount of belly, however, you'll be able to change with your rigging, so it's not so important to get it right, however, too much sewn in and you're screwed.

The more rigid the frame and the less stretch in the sail, the higher the costs due to the higher quality materials and engineering going into the rig and sails. The ultimate design goal is to have sails that have zero stretch (like perfect kite flying lines) due to the variances in wind pressure, but at the same time have perfectly controllable flex and curve by playing with the rigging and lines. The rigging itself can flex -- this helps with the control -- but needs to be controllable by the sailor and not by the wind pressure. At the same time, the wind pressure is what gives the sail its shape. It's impossible to see the curve of the sail without setting it to the wind.

so yeah, it's a complicated interweave of a whole bunch of factors. You'll have to compromise! Your head must be buzzing!

Your best entry point for ongoing research is likely windsurfing sites. If you speak french, they're the most extreme sailors and have far less respect for copyright than anglos... :evil:

Nice photo above, BTW. It's so old school nobody could possibly take offense! :frog: It's hard to tell because of the angle, but it looks like about 12-14% belly, about 30-35% back from the leading edge.

Don't take my numbers with out checking them, all my sail tech books (the best ones are translations from the french) are in Hong Kong, and I'm chilling out with my family here in snowy (yeeha!) B.C., Canada...

best of luck to ya!

I must email the sail guy... :D this is getting out of control...

And what about a flat sail?... if theres lo-wind i can run it really loose to have some extra power, but if i want extra control (thats good if intending to FLY with the wing) i just tighten a few ropes and i got an almost flexless rig that copies the curve of the battens...

yeah, you're in the groove now...

ask your sail guy about the effects of adjusting tension on the battens, also you'll need to make a decision regarding batten material...

sounds like the simpler your keep your rig the quicker and cheaper you'll have something you can fly, and that will tell you how complicated you want your second design to be...

Exactly...thats the point...i need a sail quick, easy and cheap to build... to learn how to properly control it... then i will obviously want another wing, smaller, bigger, carbon tubings, otrher sail materials and more radical, task-specific-shape...who knows..... but, right now i need a school wing that works allright for allround riding... im gonna use it primarly on water (but i got some wide shores by the river (and wind over here is always from the coast :D)

I was thinking about buying a 75 liter windsurf board... an change the strap position to be perectly balanced (in a windfurf board i guess they are way too much on the rear)

And for the land... i can build a dirtsurfer from bmx parts in one day... (im already thinking about a stainless steel frame, some 28 spoke bmx rims laced to sealed bearing hubs and a 200mm+ disc brake for the rear (dont know if its useful...but it looks killer :D)

Looks like this guy went homemade on the cheap and used a tarp for a sail.

http://www.youtube.com/watch?v=JarWgs5yfAo

looks like it bent during the testing...

Heres link to mine:

http://www.powerkiteforum.com/viewthread.php?tid=6308&pa...

Like I said, tent tubes, and nylon from the rainfly, just make it man, I promise it will work :D

Hows the project coming along?