Your Own Inflatable Dome: Make It from a Kit (Jul, 1973)
Your Own Inflatable Dome: Make It from a Kit
PS brings bubble buildings into the realm of the do-it-yourselfer: Take your choice of kits in three sizesâ€”or start from scratch if you like By A. J. HAND / PS Home Workshop Editor
You’ve read about the new air-supported buildings that can cover hundreds of acres [PS, Mar. "73]. Now take a look at some pneumatics designed with you in mind. They’re inexpensive, easy to build, and adaptable to a whole range of uses.
The basic single-skin plastic dome, inflated by a small blower, can be used as a studio, greenhouse, pool cover, outdoor rec room, camping or vacation shelter, portable classroom, or storage facility.
The 25-footer shown here packs down small enough to fit your car’s trunk. Two men can set it up and inflate it in less than 30 minutes. Total weight is under 300 pounds.
If the 25-footer doesn’t fit your size needs, how about a 16- or a 34-footer? All three are available as kits. None of these is your size? Then you can design your own with help from a plans booklet.
To bring you these kits, and the plans booklet, we turned to Poor Willie Productionsâ€”a Boston-based design-development firm. They produced our prototype 25-footer, they’re supplying the kits, and they created the instruction booklet, too.
The basic skin used for all the dome kits is 12-mil vinyl film. Colored sections are nylon-reinforced Dura-Tuff (Duracote Corp., Ravenna, Ohio). Clear sections are Union Carbide’s Krene, a special vinyl formulated for greenhouses.
Both films are extremely tough.
Outdoor lifespan runs from five to 10 years. Rips and punctures are rare, but easy to fix with vinyl patches and cement.
The gore design. This is one of many solutions to the problem of building a dome from a membrane fabric that is initially flat.
The dome is broken down into small, curved sections called gores. When inflated, the gores take on a compound curvature, flowing smoothly into a dome. These gores are welded together with a heat-resistant vinyl adhesive and solvent: Bostik #7130 and methyl ethyl ketone (MEK).
The door. Although large pneumatics often require air locks at doors to prevent depressurization and collapse during heavy in-out traffic, the 25-foot prototype remains inflated even when the door is left open. The door in this case is a five-foot nylon zipper that opens and closes a slit-type entrance.
The blower. The air for all three structures is supplied by a Dayton direct-drive, squirrel-cage blower. Its 1/4-hp motor has more than enough muscle to keep the dome pumped up.
Where wind loads are small, internal air pressure can be kept low. Two psf will do. Where wind loads are more severe, you increase internal pressure. Poor Willie calculates that 10 psf will support the dome in winds up to 80 mph.
Holding the dome down. The same air pressure that supports the dome would lift it off the ground if you didn’t anchor it. Attached around the 80-foot perimeter of the prototype is a catenary sleeve of vinyl film, used to stake the dome down. Through this sleeve Poor Willie threads lengths of one-inch plastic pipe, joined to form a giant hoop. This can be staked to the ground, or fastened to a wood or plywood deck via plumber’s strap and nails or screws.
Putting a dome together. Making a Poor Willie inflatable is pretty much a scissors-and-glue operation. A full-scale gore pattern guides the cutting of the 18 gores. Patterns in the plans booklet outline the window, door, and catenary pieces.
Once you have all parts cut out, prepare the gores for assembly. This involves cementing in window inserts, and outlining all the weld seams with masking tape. Next comes assembly of the door panel. This requires repeat passes with a sewing machine, but the rest of the assembly is the normal solvent-welding procedure. After the door panel is set, assemble the catenary sleeve, blower tube, floor, and cap parts.
Now you can weld together the two gores that will take the door assembly. All gores are welded on a curved track that’s easily made from plans in the booklet. You can’t weld the gores together on a flat surfaceâ€” their edges won’t meet.
After gores are joined cut out the circular hole for the door panel and cement it in place. Then cement the blower tube into its gore.
Once the door and blower-tube gores are done, weld together the remaining gores, taking care to keep the gore bottoms aligned. It’s best to start all welds at the bottom and work toward the top. Don’t stretch the fabric, or the windows and catenary’s seam lines may not line up.
Main dome assembled? The catenary goes on next. It’s followed by the floorâ€”if you’re using one. After you finish the final floor weld, let the dome sit for a few hours; better yet, overnight.
Next day you can lay the dome out, stake it down, and hook up the blower. In minutes you’ll experience the unique feeling of standing inside your own bubble building.