|Date:||26th June 2021|
|Location:||Whalan Reserve, Australia|
|Conditions:||slight wind, sunny|
|Members:||JohnK, PaulK, GK, PK|
Today we did a series of flights to compare how much of a difference a launch tube makes to the overall altitude and what can be done to improve it even further. We used our normal Axion rocket for this. We prepared a new Clark cable-tie launcher for this experiment that allowed us to screw an ARB to the bottom of it, or remove it for experiments without it.
Originally we had the normal PVC pressure pipe on the launcher that fits very snugly into the bottle necks. There was a problem though passing this pipe through the tornado tubes, although it would fit fine through the tornado tube by itself, once tightened the bottle neck would slightly constrict making the fit very very tight. So we opted for the grey electrical PVC pipe that is 20mm in diameter rather than the 21.5mm that is the pressure pipe. This gave a snug enough launch tube but also made it easier to pass through the tornado tubes. We made a small adaptor out of some thin walled steel pipe that was glued on the inside of the two PVC pipes.
For the ARB we used one of the fiberglass reinforced spliced-quads that made up the Polaron G2 boosters. The capacity is around 5 Liters.
--- Video Coming Soon ---
For the first flight we decided to go with the full launch tube and the ARB booster. We guessed this was going to go the highest so we wanted to fly it earlier before the wind picked up. We used 1.5L of plain water for this, and pressurised it to only 100psi. We weren't looking for a specific altitude we just wanted to see the relative difference between the launch tube variants. The flight went well, though the parachute ended up getting tangled around the fins and the rocket landed nose first. No damage was done to the nosecone. We used our new AltimeterOne altimeter for these tests. The final altitude was 389 feet.
For the second flight, everything was the same, except we removed the ARB from the launcher. The flight was almost identical, and the rocket went up to an altitude of 356 feet. Which was about what we had expected. The rocket again came down nose first under parachute, and again there was no damage.
For the last flight, we swapped out the launch tube launcher, and replaced it with a normal Clark cable-tie launcher without any launch tube. Everything else for this launch was identical again. This time the rocket only flew up to 323 feet. The rocket again came down nose first, but this time there was a little more damage to the nosecone fairing. The fairing will be replaced, but all the electronics survived just fine.
The differences in altitudes were as expected, although the rocket underperformed on the launch tube launches from what the simulator predicted. We will have to have a closer look at the variance between the observed flights and the simulator results. In the video for this experiment we do a deeper dive into launch tubes and how they work.