🚀 go-pugleaf

A quote from _The Unbelievable Bubble Book_, by John Cassidy
(Klutz Press, 1987):

   Once the World's Leading Fizzicist, Dr. Aristid V. Grosse, for many years
   the director of the Research Institute at Temple University, spent his
   youth in the study of high-energy particle physics. He worked on the
   Manhattan Project, joined the faculty at Temple, became president of a
   well-known consulting company, published numerous scientific papers and
   to all appearances, pursued a dignified, as well as distinguished,
   scientific career.

   Meanwhile though, he was privately conducting a series of strange
   experiments that have made him an expert... on the subject of bizarre
   bubbles and funny foams.

   Dr. Grosse once modified a 55 gallon steel drum with a copper tube
   apparatus that looked suspiciously like a still. When connected to a tank
   of helium and a source of soapy water... the drum suddenly began to spew
   out large gobs of aerodynamic foam. "Skyfoam"... could climb to altitudes
   of 30,000 feet. As basketball-sized blobs of foam headed off into the
   blue, Dr. Grosse would speculate on the... practical applications. 

   Speculation, incidentally, whether practical or not, was Dr. Grosse's
   strength. Once, after wondering about the ability of huge blobs of foam
   to quell street riots, he buried himself in a tankful of a specially
   formulated foam. "You can't see a thing," he reported back. "You can't
   hear a person three feet away unless he shouts."

   Dr. Grosse used to experiment with special formulations of bubble solution
   that could generate gel-like bubbles with some very peculiar un-bubbly
   properties... they could be decorated and hung around a room like party
   balloons. Dr. Gross had several in his office with sequins on them...
   He even had plans involving the creation of a 40 foot long hot-dog shaped
   gel-bubble that would function as a parade float.

I've been unable to locate Dr. Gross through Temple University. I wonder
what he might have proposed for the roof of the structure below?

It might have a 9' tall strawbale and mortar wall with a commercial plastic
film greenhouse on top, one 30' wide made with curved galvanized pipes on 4'
centers and two layers of inflated polyethylene film stretched over that, a
standard commercial film greenhouse technique, except for the stemwall. Such
a greenhouse top, eg a "Northerner" from E C Geiger, might cost about $1 per
square foot, but that seems expensive, and it would not be well-insulated, 
with an R-value of 1.2.

Perhaps we could put a lightweight air-supported roof over the 30 x 58'
rectangle between the chicken coop and the greenhouse, like this:

         straw 
 .....................
 .s                  .
 .t                  . straw                             N
 .r     chicken coop . 12'                      |       16'     |
 Aa                  ...........................................A
 .w                  .      straw wall          ................. ---
 ................................................       .       .
 .   .    20'        |        <- 30' ->         .       .       .
 . s .         .         .         .            .       .       .
 . t .                                          .       .       .
 . r .         38' x 66' membrane cover         .       .       .
 . a .         .         .         .            .       .       .
 . w . |                                        .       .       .
 .   .   .   post .    post   .  post  . W  post.   .   .       . 32' E
 . w .26'                                       .       .       .
 . a .         .         .         .            .       .       .
 . l . |                                        .       .       .
 . l .         .         .         .            .       .       .
 .   .                                          .       .       .
 .   ............................................       .       . 
 .                  straw wall                  .       .       .  
 .....................................................glass...... ---
 .                          4'           solar wall             .
 A..............................................................A..........
                                                                          .
                                                                          .
                          reflecting pool                                 .
  16'           made from a single roll of 20' wide                       .
                    EPDM rubber roofing material                          .
                                                                          .
                          <-- 100' -->                                    .
 <.........................................................................

                            .                   S
         .       air-inflated cover?          .

 A..............................................................A ---
 .                   .                             .        .   . ~4'
 .                   .                          .               . ---     
 .   chicken coop    .                          . c           c .        
 .                   .      9' tall solar wall  . T c       c   . ~5'   
 .                   .                          B i p       p i B      
 .                   .                          B w p       p w B         .
..............................................................................

The cover might attach along lines with corners marked A above. It could
be rectangular in shape, as seen from above, and curved as seen from the
east or south.

Suppose the roof support had four posts, 9' tall, with EW and NS ceiling
joists and NS ropes with a 15' span on 4' centers, that sagged 2' down from
the 9' wall edges at a point midway between the long walls and the EW joists.
With a 15 psf snow load, each rope would have to support 960 pounds, ie a
vertical tension of Ty = 480 pounds on each side of the center, with a
horizontal tension Tx = 4Ty such that the rope tension T = sqr(Tx^2+Ty^2)
= sqr(17Ty^2) = 1980 lb. Let's see... The breaking strength of 1/8" dacron
rope is something like 600 pounds, so 1/4" rope might work. Perhaps 1/2" rope
for a safety factor of 5. 

The EW beam would support about 2000 pounds over a 12' span, so if
f = 1200 psi, L = 12', W = 2000, M = 2000x12x12/8 = 36K in-lb, 
S = 36K/1.2K = 30 in^3, and if b = 4.5" d = sqr(6S/b) = 6.32".
We might use 3 2x8s for the EW beam. 

On top of the beam and the ropes we might have a layer of 30% black
greenhouse shadecloth, eg Stuppy's item number 2363, costing $0.088
per square foot, with a small additional charge for sewing it into a
30 x 58' piece with hems and grommets along the edges.

On top of that might be a layer of UV resistant greenhouse polyethylene
film, eg E C Geiger's catalog number 23-3432100, a 4 mil clear poly film 
in a 32' wide folded roll costing about 5 cents/ft^2. On top of that
might be a layer of 6 mil film, and they might be attached at the edges
with E C Geiger's Unilock aluminum extrusion clamps, costing about
64 cents/linear foot.

Then we might have another layer of shadecloth over the top with a few
grommets in the middle for some ropes on 4' centers over the top to
stabilize the top in the wind and resist inflation forces. The top might
bulge up 3' in the middle, and it might be whitewashed in summer. The upper
poly film might need replacing and recycling every 5 years.

Here's what Stuppy has to say about inflation: "a rule of thumb is: for
every 10,000 square feet of pillow area, use a one-thirtieth (1/30)
horsepower blower." Yeager's new 30 x 80' greenhouse on route 113 south
of Phoenixville, PA uses one such 50 watt blower for inflation. Stuppy
recommends inflating unsupported poly film pillows to a pressure of 0.3" WG.
With shadecloth and rope backing the films might be inflated to a higher
pressure, making a sturdier structure.

How would we insulate this roof? Bubbles, of course.

Nick