We didn't get to fly this weekend due to the adverse weather conditions, but at least we made progress on the Polaron IV rocket. The 8L rocket main stage pressure vessel is now finished, with reinforcement of the bottle bases based on the technique described during our last update. We had to machine up a new base to base coupling that was longer than normal because it has to go through 4 thick PET walls with washers in between. When we now heat shrink the reinforcing sleeves, we fill the inner bottle completely with water and pressurise it to about 15psi. We also use a blow torch set to a low flame to get better control over the heating location.
We have yet to pressure test the main stage, but I am hoping that 130psi will be a safe launch pressure. After a couple of failures at 120psi of similar Robinson coupled 2-liter bottles, we have been reluctant to push the pressures much higher. Hopefully this reinforcement technique will allow us to do that.
We have also started modeling some of the launcher components and staging mechanisms in 3DStudio Max to get a better idea how it's all going to fit together. It also allows us to check for clearances before cutting any metal.
Dad has also prepared hoses and another pressure regulator that goes up to 25 bar (~360psi) with the associated high and low pressure gauges. This will allow us to launch a rocket with a different pressure to that of the boosters. This way we can optimize the performance depending on the structural integrity of the different elements.