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i'd think air would be better because, although the volume of air pumped into a kite is not particularly large to warrant such a crazy explanation, 100% CO2 is a heavier gas (~50% ) than air (assumed to be 80% N2 and 20% O2). So it's denser(require more lift to stay afloat), and the kite would be more sluggish because of its increase in inertia.
people have definitely tried helium before. The main downside is its expensive. I'm pretty sure the reported benefits of using helium are slim to unnoticeable, some say they can feel the kite feels more responsive, but who really knows? I'd like to do a randomized double-blind study, my major confounding variable might be wind speed...
yeppers i'm an idiot.
I've used helium a couple of different times several years ago at Sherman on the dreaded north wind days. For those of you who haven't kited there on north winds (and were probably wondering why no one does it), the wind tends be be very gusty, and more importantly, very holey. One minute you're screaming across the water totally overpowered and out of control in a gust, and then just a few seconds later your kite falls out of the sky on a big lull. Not much fun on old-style, no-range C kites like the Naish X2s that I was riding at the time.
I figured that filling the struts and leading edge with helium might keep the kite from falling in the lulls, so I gave it a shot. It worked pretty much as expected. In medium lulls that would have dropped an air filled kite, the kite would stay in the air. In big lulls, the kite would start to fall very slowly but would often recover when the wind picked back up again 10-20 seconds later. Only in the biggest lulls would the kite fall, ever so lightly, to the water. And when that did happen, the really cool thing was that the kite would rest on the on water on the very tips of the ends of the struts, ready to hot-launch quickly as soon as the wind picked up in the slightest again.
I didn't notice any difference in the way the kite handled due to it's somewhat lighter mass. Though I think it's unlikely that it is even noticeable, it's possible that it does make a small difference. At any rate, crappy north winds at Sherman is no place to try to make such judgments. A difference in handling would be much easier to determine with very steady winds.
So, if it worked so well, why don't I go to Sherman anymore in the north winds and fill my kite with helium and tear the place up all to myself? Because the north wind still totally sucks there and even if the kite stays in the air in a moderate lull, it's really not providing any lift and you can't maintain planing speed and will sink down into the chilly water anyway. In other words, still no fun in gusty/holey winds even when using helium and riding with nice modern rangy kites.
Also, without using some kind of recovery system to get the helium back out of the kite and into the helium tank at the end of the session, it's a bit expensive. I used a party helium balloon tank that I bought at a local party store. It cost around $40, and I was able to pump up 2 kites (I think 12m both times, but may have been 12m once and 10m once), with still a bit remaining in the tank. That comes out to probably at least $15 per session. It would probably be much more cost effective to use an industrial grade helium tank instead of the party balloon tank, but then who wants to carry one of those large, heavy steel cylinders around all the time. After all, many of us switched from windsurfing to kiting to reduce equipment bulk and weight, not to add to it.
Finally, there is one more problem with using helium -- the tiny helium molecule has a much easier time leaking out of the bladders than normal nitrogen and oxygen molecules making up air. My leading edge was noticeably soft after only about 30 minutes of riding. So if you give helium a try, keep the session short, or be on the lookout during your session for any signs of a soft leading edge.
You may be wondering if it's a good idea to use helium when riding at the coast, so that if you screw up and dump your kite in the water the helium might help it to relaunch before it gets pounded in the surf. I haven't tried it and I don't know. But I suspect that when the kite gets dumped in the water like that, it will get too wet too quickly for the helium to be effective. Anybody who wants to try it is welcome to the remainder of the helium in my party balloon tank
While it's intuitive that helium wouldn't make a material difference, I took the trouble to do the actual calculations! http://theideafactoryonline.org/helium-filled-kites/
To "lift" your kite? It would take some 2500 liters or so to make it neutrally buoyant (at 1 atm) if it weighs ~2.5kg. Someone else can do the math at kite pressure.
Now, back to work on my perpetual motion machine.
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