Airship Envelopes, economic show-stopper

Hi, this is Allen from skyboat.wikispaces.com

   I just had the startling realization that there can be no cheap personal Skyboat without a cheap envelope. I mean at least a factor of ten cheaper than the exotic gas-tight super-stitched bags of today.

   To avoid the economic DOOM of gas-tight fabric, a cheap airship MUST NOT use it. Lift Gas can be contained in a hundred or two, OTS, (Off The Shelf), latex meterological balloons.  See clusterballoon.org

   Then the aerodynamic skin of the Skyboat can be made from plastic tarpaulin film, glued together, not stitched. Faster, Easier and Cheaper, bringing Skyboating within range of workin' slobs.
 
UP!

Why are lots of balloons better than one big one?

I'll give one reason and let other members jump right in and name other reasons for preferring to have multiple internal balloons, or negative reasons if they have doubts.
One hundred fifty weather balloons are better than one or two huge gas bags because the home builder doesn't have to buy a sewing machine and spend months cutting perfect gores and then stitch, stitch, stitching all of those seams!
How many people would buy sailboats if they had to sew all the sails? Answer, a fraction of those that do.

I was also pondering the idea of smaller balloons.  The original Aereon used 21 separate compartments in it's 3 hull design.  This kept Dr. Andrews hydrogen (I believe that is what he used?) from shifting in his envelope when tilting his craft up.

I'm leaning towards checking on pricing for "super pressure" balloons....

http://images.google.com/imgres?imgurl=http://www.aero.jussieu.fr/projet/HIBISCUS/images/test_BP_web.jpg&imgrefurl=http://www.aero.jussieu.fr/projet/HIBISCUS/en/many/spb.html&usg=__jd1MsugDW2goWjiVEl7dWHKFQmc=&h=640&w=512&sz=61&hl=en&start=2&tbnid=3XtFdG3eUJ6kTM:&tbnh=137&tbnw=110&prev=/images%3Fq%3Dsuper%2Bpressure%2Bballoons%26gbv%3D2%26hl%3Den

http://en.wikipedia.org/wiki/Superpressure_balloon

http://www.britannica.com/EBchecked/topic/1442976/superpressure-balloon

Historical development » Superpressure balloons  

Polyester film at a tensile strength of 1,400 kg per square cm (20,000 pounds per square inch)—compared with polyethylene at a tensile strength of about 40 kg per square cm (600 pounds per square inch)—finally made it possible to produce superpressure balloons, which do not expand or contract as the enclosed gas heats up or cools down. A series of contracts were awarded to the G.T. Schjeldahl Company by the U.S. Air Force in the late 1950s to develop polyester balloons. After repeated failures, Donald Piccard (son of Jean and Jeannette Piccard) was assigned the project. He theorized that the failures were caused by the self-destructive tendencies of the stiff film. By laminating two layers of very thin Mylar, he produced a more flexible film that resulted in the first successful superpressure balloon. These balloons have been used by the U.S. National Center for Atmospheric Research to carry instrumentation aloft for months at a time, continually circumnavigating Earth.

Manned superpressure balloons have had some success but have not yet been able to carry on through diurnal heating cycles.

http://adsabs.harvard.edu/abs/2009AdSpR..44...23C

It seems we are assuming that many small balloons can be purchased and one large balloon must be built.

 But, why can't one large balloon be purchased? I believe that the best method for proliferating blimps is to use a kit program.  The most difficult parts can be manufactured in one place and then assembled by the individual of club wanting the blimp.

It depends on where you get your envelope from. There are some other manufacturing options that produce very good work at a fraction of the cost of the 'big boys'.

I have used them on unmanned ships before.

What is the envelope material in the above ship?  

Can you put together an estimate of what a 8 meter sphere and a 3m sphere would cost?
  
And what is the estimated envelope weight and estimated lift of each?  

(I'll be plugging in the numbers for my design concept).

Copied the below from an article about Nasa's internal "vote for" competition that voted the superpressure balloons as the best project, or something like that....

"Last week, Debbie Fairbrother, chief technologist for NASA's balloon program, gave me an overview of the SPB project. Unlike NASA's workhorse zero-pressure high-altitude balloons, which vent gas (helium) during the daytime when heated to full inflation, and contract at night when the gas cools (sometimes causing the balloons to descend 10,000 feet or more at night), super pressure balloons are fully pressurized, insulating them from the vagaries of temperature, providing greater stability and the potential for much longer flights. A January test flight launched from Antarctica, in which the balloon maintained an altitude of 110,000 feet, stayed aloft for 54 days, compared with a few weeks for a standard zero-pressure balloon. The pumpkin-shaped balloon uses a lightweight polyethylene film as its skin.

When development is complete, super pressure balloons will be able to carry payloads of several tons above 99 percent of Earth's atmosphere on missions of 100 days or more. NASA's current high-altitude balloons carry instruments such as telescopes and cosmic-ray detectors (and much more economically than an orbiting satellite mission); the payloads can be retrieved and reused once the flight is over. Earth scientists are also expressing interest in the use of super pressure balloons. Lastly, they could also potentially be used in missions to other planets, where they would stay aloft for an extended period in the planet's upper atmosphere."

If we want to buy the envelope rather than build it, we need to contact the companies that are out there and get an idea about their price structure. Do they charge by the volume or the surface area?

Knowing the pricing structure will allow us to design a blimp that gets the most bang for the buck. We need to start compiling a list of possible contractors we can use for components we want to outsource. 

Here is a start.
http://www.myairship.com/database/index.html

Re buying an envelope, they are not OTS items, they are custom sewn for the manufacturer because there's no regular market for envelopes. If true, that means the home builder must buy the expensive material and sew, sew, sew, throwing lots of it away.  yuck.
   Back to my point: it's easier and funner to tape and glue a cheap plastic sheet of an envelope and stuff it with ten dollar sounding balloons which were filled with hydrogen from my own electrolyzer.
   I'm looking for dudes to research this craft with me at skyboat.wikispaces.com
high cheers, AllenM

But the whole point is to allow the home builder not to sew or glue or tape together an envelope if they don't want to. We can build the envelopes in one place over and over agian. This way we can keep costs low and take care of one of the most difficult parts of the build.

Or we can buy the envelopes from a manufacturer and we will still be able to reduce costs by buying in bulk.

Many small balloons also fill space inefficiently. This will increase volume, drag, and weight. 

Sphere packing of similar sized spheres has a maximum efficiency of less than 75%. And if you just pack the spheres in randomly without arranging them, the maximum efficiency will be less than 64%.

Not to mention the problem of leakage and refilling scores or hundreds of individual balloons.

     Not scores, just maybe six to twelve, similar to the early zeps.  If you look at a mylar party balloon, it's much like the gas bags of old.  That shape would stack well, using smaller ones at the ends.  Of course, they would be custom made by the party balloon people.  I would then have a small tube from each to a master connection for monitoring. 
      Somewhere in the mix will have to be a balloonett, it probably can be the same stuff.
      The party balloons will be handy for scale modeling of the ship.  Modeling is a good way to work out construction and engineering bugs.

Are you talking about stacking the bags from front to back with disk shaped bags? I think that is a reasonable approach. It is sphere stacking that I think is inadvisable.

Yeah, disk shaped like the big guys did.  Maybe even doughnut shaped if I continue with my desire for a tunnel drive.  The tunnel would be handy for accessing stuff from the inside.  I just like the idea of the motor in the center, easy to balance, only need one motor, active steering.

Okay, I'm back, went to Europe this summer. Saw the Varialift proof-of-concept vehicle under construction. It's gonna work. Variable buoyancy is here. Alan Handley knows what he's doing and how to do it.

The topic is expensive exotic gas-proof envelopes are a show stopper. We seem to have decided that buying mass-produced balloons [of whatever optimum shape to thoroughly fill the envelope] for interior flotation is easier, funner and quicker than putzing around for months with a sewing machine and scissors making weird-shaped interior lift bladders to fit the envelope's shape. [That would require OCB, obsessive compulsive behavior. I'd rather be flying, I just wanna fly.]

Next, we need to find a tough, windproof, cheap plastic skin for the personal affordable skyboat. There are many types of plastic sheeting which would work. The great good news is that the skin no longer has to be gas proof. [I'm not actually sure that plastic netting is not out of the question for the skin.] It can be a cheap covering with glued seams which took all day to glue, not a month to sew as with exotic envelopes.
Keep looking up and thinking higher!!!

If you use a netting, air will penetrate into the "envelope" and brush up against all of the individual balloons. That will cause more drag, and that drag may be unstable and unpredictable if the balloons wobble during flight.

If you want to use small prefab balloons, then you might want to consider tubes instead of spheres. They will pack tighter, will more closely fit the shape of a blimp, and provide some stiffness. 

BTW, if you plan on using hydrogen, you don't really have to have exotic bag materials anyway because hydrogen leaks much slower than helium.

     Have the Varialift folks done gyroscopic stability tests on their design? I was working on an invention, and borrowed a large electric gyro from a friend. He explained to me that if you have four gyros mounted to a solid platform they inter-react. This test would require strong gyros under power, not coasting. You can imagine one of the lift rotors on the Varialift powering up, lifting it's corner. The other three gyros are going to be torqued, and will precess. As they precess, they torque the platform. Gyro hell. I hope I'm wrong.
     Otherwise, all is well. Definitely like your approach. The plastic I have been looking at (PETG) is real tough, holds a fold, thermoforms, and heat welds. The commercial welders cost a fortune ($5K), but I think a spot welder could be made DIY. I've been posting about using a standing seam (like roofing) and keeping the gores identical for $implicity. It's a little heavy, may have to go less than 20 gauge (.020")