|24th June 2023
|Whalan Reserve, Australia
|light winds ~5km/h, 15C Mostly Sunny
This week is a follow up to the air bag inflation experiment we did a couple of weeks ago. I wanted to say thank you to everyone who commented on the video suggesting ways to improve the experiment. The general consensus was to have a container of some fixed volume with rigid walls that couldn't expand and then connect a thin tube to it to indicate the small change in volume as the pressure changed. So this week we performed the following two experiments.
We got a can from powdered chocolate milk because it has an airtight removable lid. The whole can is light and it shouldn't expand/contract with the small pressure changes. We then drilled a hole in the lid so that we could pass a flexible tube through it. We went with the suggestion to make a U-bend in some flexible hosing and partially fill it with water. The problem with a straight U-bend is that you'll likely to spill some of that water, and it might miss behave under acceleration. So we spiralled the tube on a piece of corriflute and mounted it above the can with a bracket. This way we could see the water from above, and it shouldn't spill if the whole thing was turned upside down.
We then got some food colouring and mixed it with a small amount of water and sucked up some liquid so that it was in the middle of the spiral. This way the liquid could move one way or the other as needed. This setup was quite sensitive as just warming the can with my hands you could clearly see the pressure increase as the liquid moved around the spiral. We used a couple of cable ties to mount the whole experiment inside the fairing. The nosecone again with the downward facing camera was mounted on top and the whole thing was taped to the top of the rocket.
During boost you can see the meniscus get flattened, but after burnout it goes back to normal. You can see clearly that the pressure starts decreasing outside the can as the rocket goes up, and the water starts spiralling out. Just as the parachute deployed with the rocket pointing down, there was enough water in the open and downward facing tube, that the negative G-s forced it out and it syphoned out the rest of the water from the tube.
The open end of the tube had just pointing up the inside of the rocket.
For the second experiment, we closed off the end of the tube with a small deflated water balloon. Hopefully this time we would see this inflate a little as the rocket went up.
The rocket was prepped the same way as before and we pressurised the rocket to 110psi. In the on-board video you can clearly see that the balloon had inflated on the way up. On the way down, you could also see from the backward movement of the water that the pressure increased again.
So this approach definitely made the whole experiment much more sensitive and the change in pressure was clearly visible.
We flew Brian's flight computer again a couple of times on our rocket so he could gather some more data. Both flights went well, and later Brian shared his data with us.
Here are the data files for those two flights: