We repaired the test air beam then glued support strips over the end seams. The end cap was changed to add another inner cell clamp. The strength is good, it will sit and hold 3.05 psi all day. The seals still don’t cut it. I had to keep the compressor running continuously to maintain pressure. The next goal is to make a wider seal without adding any weight.
Archive for December, 2008
Anthony gave a shout of “Open the Valve!” as the end began to let go. It was all too fast. The foam and glass end cap went hurling across the shop. Work continues on our gossamer pressure vessels. Solving one problem allows you to push into a new level of problems. Today was no different. We had two solutions to test. A glued seam reinforcement and fiberglass channels in the end caps. For this round we used the six foot straight air beam instead of Ascender test rib.
The new glue reinforced seam was a big success. The sewn seam alone has big stretch issues above 1.7 psi and starts to fail just above 2 psi. The new seam handled 2.4 psi without any signs of stress. The fiberglass on the end cap channels were still not sure about. The harder surface held up better but was much harder to seal.
The new issue we discover was the strength, or lack of strength, of the nylon shell end closure. At a touch over 2.4 psi it all let go.
While we were shooting giant pellets past his head Mark was steadfastly getting pocket sewn for the new launch bag.
I couldn’t resist going to the shop for a little pre-turkey fiberglassing.
These are the new rib end caps. We’re fiberglassing the channel around the perimeter. This will make a stiffer backing for the rubber seal. One cap will get high and low volume valves and a pressure gauge. Both will get a smaller foam disk glued to it for stiffness.
Any bets for 3 psi on Saturday anyone?
We took a break on rib work to catch up on some other projects.
We nearly completed refurbishing rocket launch box. The last touches included mounting stops on the base of the internal rail, this prevents the rocket from sliding out of the bottom, an important feature, sealing the box, attaching the external support rings and making and gluing on forty foam gussets.
We sold two of our balloon launch bags. This means it’s time to breakout the sewing machines and make some more! The team cut out the twenty-eight foot fabric panels, ten in all. Next all the panels will be hemmed, then the 240 pocket, all with Velcro closures get made and added then the attachment loops and tear panels….. If we are sewing our way to space, are we there yet?
We need to find a adhesive that will bond the silicone/Nylon fabric we use. We bought a set of candidates glues and have begun trials. I wasn’t expecting a success in the first batch. However number five in the first ten passed load under flex test. We’ll be using the adhesive to reinforce a rib seam. Before applying it to a full rib we’ll test it out on a six foot straight air beam. That will also give us a chance to test another upgrade to the rib end caps.
A big thank you to Shawn Carlson for this one:
The rib design is evolving nicely. The big advances are coming from the inner cell interfaces. Last Wednesday we had one of the ribs up to 1.6 psi. At this pressure the rib was able to support a 44 pound end load without distorting the ellipse. This is about what we need. Now the task is to get the rib to handle double that to give us a safety margin.
On Saturday we made two new inner cells and completed the third version of the cell interface. We’ve discovered that the techniques used to put the inner cell into the outer shell have a huge impact on the pressure that can be reached.
After a long day we were beginning to show real results. At 9pm we went for a full pressure load with all the bells and whistles in place. At 1.7 psi we began hearing loud bangs as banding threads started popping. The banding threads were an idea we tried that didn’t workout so apart from startling us it didn’t matter. We closed all the valves and everything was holding. Back on with the compressor. At 1.92 psi there was a huge pop, a blast of air then just the sound of the compressor. A three foot section of the outer shell had blow out.
These first test rib outer shells have been simple single seamed creatures. They’ve gone as far as they can go. Now it’s time to build a true double balloon seam and load tape ribs. Although we may do a patch and add some load bands to the existing pair of ribs just to see how high they’ll go. That will give us a better handle on failure modes.
With each test the rib changes. We’ve gone from multiple side access panels to drawstring end closures, narrowed the diameter of the inner cell, increased the overall ellipse circumference and a dozen other modifications. For the rib to act as an airbeam we need to get it to 2 psi. Now for the rocket guys that may sound like no pressure at all. For the balloon folks that is a huge number. The current configurations have gotten us just over 1 psi. Still a long, long way to go.
In the last couple of days we’ve been building ridged end caps and a new fill and gauge interface. We’ll be reaching for the magic 2 psi tonight.
Here’s some images from last Saturdays work session: