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16943[ksurf] Re: more helium in sleds...

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  • Dave Culp
    Aug 1, 2000
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      Dave Raue:
      >I'm not sure which part isn't true. The point isn't that He can't be
      >used, contained, compressed, etc. Obviously it can. It's that doing
      >so in a practical, cost effective fashion isn't likely. Metalized
      >mylar has pretty poor puncture resistance. And the context of the
      >thread was as an inflation medium for Naish/Wipika designs. These
      >have relatively small inflatable volumes that need to be at
      >relatively high pressure since they provide structural support. It's
      >pretty obvious that somebody could construct a sealed, inflatable
      >foil. Making one that would survive sand fences, thorns, etc would
      >be more challenging and expensive.

      Guess I'm going to have to ask you for some definitions, Dave. Yes,
      the thread is "more helium in sleds." OK, I guess I'll grant you that
      Naish's are "sleds," though I can find no reference work that so
      defines them (including both Wipika's and Naish's web sites) And yes,
      we established, long ago, that trying to get any value from putting
      helium into the tubes of a Naish or Wipika was a *total* waste of
      time. You're better off putting helium in your bike's tires, then
      trying to fly the bike. We've *covered* all this, in this
      interminable thread. Forgive me, I was under the impression we'd
      moved on, and were discussing putting helium into any *other* types
      of kites, where it might be actually, physically possible for it to
      have some effect.

      Having said that, we (you!) were discussing 1) permeability of
      fabric, and the general expense/impossibility of same, and 2)
      re-compressing helium via mechanical pumps. (Is anyone else on the
      same page? Is anyone else even listening??)

      If I were asked to build a helium-filled kite, I wouldn't use a
      single bit of either fabric or film, but a combination, just as
      inflatable boats use (plastic bladder, inside fabric cells). In fact,
      I *have* done this, with good results. No, I'm not going to teach you
      how to do it, nor reveal my suppliers to you. Sorry.

      Now, you said:
      >... He is going to diffuse out of your bladder like mad. On an
      >atomic scale the baldder is quite porous, like microscopic
      >chickenwire. Chicken wire keeps the chickens in, but it doesn't do
      >much to keep out the mosquitos. Plasma metalization of the bladder
      >perhaps? Otherwise, better get the boys from duPont working on a new
      >bladder material...

      From this, I presume you are talking about bladder material, and
      about helium permeability, of bladder material. Sorry to be pedantic,
      but you keep changing the subject. Real, cheap films already exist,
      they do not need to be developed (I expect DuPont makes some, but I
      haven't checked; I use another manufacturer). They are relatively
      *very* impervious to small molecules, such as helium; much better
      than aluminized mylar, for instance. Weights on the order of half an
      oz/yard can be had. Unsuitable for kitemaking; we're talking about
      *bladder* material (see above; your words, Dave).

      To inflation pressures. I hope we've already determined the issue of
      Naish/Wipika inflation pressures to be moot, with any relation to
      helium, but for what it's worth, I think I answered that one, too. By
      mouth, you are physically unable to exceed about 5 lbs. Certainly 30
      lbs is silly--you put that much in your automobile, then carry 4-5000
      pounds of car around, on 4 little half sq ft patches. It's not
      necessary to argue the point, though. You've got the kite? A pressure
      guage's less than $20 at any hardware store. If you unwrap it
      carefully, you could likely return it for a refund after you measure
      the pressure in your Naish.

      > > I've yet to meet the man capable of 5lbs, PSIG,
      > > by mouth inflation. Doesn't mean there aren't several candidates
      > > here!)
      >
      >I hope I'm one of this rarefied group ;-)

      Well, yes, now you mention it... :-)

      >I think not. The original thread was about inflatable sleds, not
      >foils or flying mattresses. You're not suggesting that the volume of
      >a 15m AR5 is 570 l or even 5700 l are you?

      Well, yes, I am going to suggest you've made yet another arithmetic
      error. Sorry. ;-)

      >Assume that a AR5
      >bladders are about 20cm diam cylinder 5 meters long (for 15.5m??). I
      >get a volume of about 37 l, even less than my estimate of 57 l.

      A "square" tube (no taper) 20 cm by 5 meters will contain about 0.157
      cubic meters, or 157 liters. I've never measured an AR5, but suspect
      the average tube diameter is a good bit more than 8" (20cm). Perhaps
      you took the number from me? I was referring to an average thickness,
      for a foil.

      >>You cannot pump helium with "squirrel cage" type compressors or
      >>fans. The molecule has too little mass; is too light weight (duh)
      >>for these to work effectively. Nothing to do with molecule size.
      >>Squirrel cage

      >Sorry, it has everything to do with molecule size. Size relates to
      >electron configuration which relates to atomic number (as a glance at
      >the periodic table will indicate) and both are lead to design
      >considerations. A chemist will see the size and mass as interrelated
      >functions of atomic weight and electron configuration. Tell him the
      >size and he knows the mass. Perhaps an engineer can take the more
      >simplified view of atoms/molecules as dimensionless point masses?
      >Anyway, diffusion relates directly to size and influences valve,
      >container, and material design (the chickenwire metaphor). In any
      >case, taking a tire pump or sears air compressor to the beach ain't
      >gonna work (which I guess you concur with?).

      Back to semantics again. We seemed changed the subject (*you* changed
      the subject), away from fabric permeability, to compressibility and
      handling of gasses inside metal devices (pumps). I thought I was
      being pedantic again, but if you'll read your own post, Dave, you
      stopped talking about permeability, and switched to gas compression.
      My comments relate to gas handling, not fabric, which I covered
      earlier.

      Let's not split hairs, though: Sure, you're right, molecule size is
      all important, with regards to fabric permeability. OTOH, your
      chemistry lesson holds little water, and demonstrates why chemists
      don't build kites. Which is smaller, Dave, a molecule of helium or a
      molecule of hydrogen? A molecule of ordinary air, or of water?
      (*answers at the end of the post. Don't cheat--give it a guess before
      you look!)

      Last, FWIW, I *do* take an oversized tire pump to the beach. I use it
      for sucking gas *out* of the kite, and exhausting it onto the
      atmosphere.

      > > OK, OK. Physics in *small* bites. I get it... :-)
      >
      >Bring it on dude, bring it on!! :-))

      OK. Hydrogen, when it exists as a pure gas, is a diatomic molecule.
      That is, it's two atoms, connected together. Helium, which is inert,
      is a monatomic molecule--a single atom, floating free. Though
      physically, a hydrogen atom is of smaller diameter than a helium atom
      (though nowhere near 1/2 the size, as its atomic weight might suggest
      to Dave's chemist), two hydrogen molecules connected together are
      quite a bit larger than a single helium atom, so the first answer is
      "helium."

      Similarly, both oxygen and nitrogen, which together make up about
      98-99% of air, are diatomic molecules. Two atoms of oxy or two atoms
      of nitrogen, always connected together. Water, H2O, has three atoms,
      but it's a biggish oxygen atom, connected to two tiny hydrogen atoms.
      Overall, the water molecule is smaller than either oxygen or nitrogen
      molecules. Yes, there are devices which are demonstrably "air-tight"
      and yet will leak water. Usually water vapor, but the stuff gets in
      and wreaks havoc with fine instruments and connections, even so.

      You don't need to take my word on either of these; ask any
      high-school or college chemistry teacher.

      Dave Culp
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