Balloon Launch Discussion

Just found a great source for BIG THIN balloon plastic, Home Depot.
Home Depot now lists .31 Mil plastic in 12' x 400' rolls for $26.80!

http://www.homedepot.com/webapp/wcs/sto ... yID=502504

Have you seen it any cheaper or thinner?

MIsterQED
Team Daedalus

QED
Yep, that looks like a viable source. I expect we will see if we can impliment that in the next round of experiments. Thanks for the positive input.

Monroe
Team Prometheus

Congrats to JPA for another great mission !

Monroe
Team Prometheus

I can appreciate the work you are doing to make a balloon but why is it important to have a nice ball shaped, round balloon. The pay load does not care what shape the balloon is. A flat square bag will work just as well, be easier to make and requires no templates or vacume tables. KISS. If you set up the sealing apparatus stationary you can feed the plastic through just like a sewing machine to do only long straight seams. Simple, cheap and easy ( just like me ) If you really need the ball shape you can modify the square bag by folding in "darts" along the top and bottom diameters. No patterns or tables to mess with.
Next balloon launch could we send up a small rocket ( 3 ft Estes) to check stability in the thin air?

I don't really think making the balloons from scratch is the best idea, but I will defend making them spherical.

What you can lift with a balloon is determined by the volume of the balloon and the weight of it. A sphere gives you the most volume for the least weight.

A balloon is also a pressure vessel, to a degree, and has to withstand aerodynamic loading as it flies through turbulence. There too a sphere is the most efficient shape, for the same reason that our tanks and Armadillo's tanks are spherical.

For the trade off in simplicity I would still go with the big bag theory. Unless you fill the bag to near bursting the gas will form its own ball shape in the bag and you will get a spherical shape. The balloon is not a pressure vessel. It is a simple container for gas.

The balloon designed to get the very best lift possible. To do that you need to maximize lift gas volume and minimize envelope and support hardware weight. If we just wanted to get the most volume per envelope weight, then the sphere is the way to go, but since we have to support a significant payload weight below the balloon we switch to a sphere over truncated cone arrangement. The common design is a sphere which has 40 degree cone on the bottom. The reason being is that the envelope is VERY weak. To evenly distribute the load from the payload to the balloon would requires some system that transfers the support for the payload to the sphere. This could be done with many fine strings, but it is lighter to just taper the envelope down to where a circular support loop can be attached. This eliminates the stress concentrations caused by auxiliary strings and does it in such a way that is enlarges the included volume.

As for whether the balloon should be made, all I have to say is the N-Prize budget for the creation of a MASSIVE zero pressure balloon would be <$30 and it would replace many $70 latex balloons. For lifting any real mass, as will be needed for an N-Prize attempt, you would need not only dozens of latex balloons, but a system that will keep them all separated enough for them to work efficiently. A homemade zero pressure balloon could be scaled to whatever payload you finally end up with.

MisterQED
Team Daedalus

I had a great idea for a plastic welding machine. A hair straightening iron. Small, light and of sufficient heat and can be bought at a yard sale or second hand store for a buck. A voltage regulator (plug in dimmer switch) to control the heat and presto a hand held seam welder. A wrap of paper around the elements should prevent sticking.

My idea is a bit more expensive, but more tunable for the purpose, a Weller digital soldering station. It's expensive, but you will probably need it for other tasks before you launch anyway, so a solid investment.

MisterQED

The Hydrogen Generator worked! We launched a trashbag this afternoon it was a fun experiment! So now we know what it takes to make enough gas to lift our next payload. I used Swarf from the lathe and man did that react! There is a lot of heat but that will actually make it ez'er for us to knock the moisture out of it buy cooling the gas down rapidly. We will need an accumulator tank to make sure no foam gets into our dryer system. Pressure won't be a problem I could get 15psi from this generator if we need it!

Monroe

I guess it is about time to get off my butt and finish up my plastic welder.

Woody!
Yeah go for it!

Monroe

Update! Dave Hein did a great animation of the balloon launch. http://www.youtube.com/user/DaveHein#p/ ... Z0Kpr5pNKE We are constructing the Prototype Spin Launcher (Brian Beckus) there are photo's on our blog. http://teamprometheus.org/movies/Blog.html (That works for everyone now thanks to Sigurd) We tested our theory and the hydrogen generator worked! Our next move is the actual balloon.

Monroe

Update!
We successfully made our first zero pressure balloon! http://teamprometheus.org/movies/2009_1 ... chive.html It was not nearly as hard to build as we thought thanks to Stew Lilley's Vacuum table and gore pattern set up! Anybody need one?

Monroe

How thin can we go before we worry about durability and the porosity of the plastic when filled with hydrogen?