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.
The first and third cell interface.
