Test Stand Rollout
This is part 2 in a series covering UB SEDS’s roll out of a test stand to support our in-house propellant program.
- Part 1 – Smoke Test
- Part 2 – Backboard Test
- Part 3 – Test Stand Structural Test
- Part 4 – Test Stand Electronics Test
- Part 5 – Test Stand Final Check Out
If you just want to skip to the end and see the test stand page, you can find that here.
If you want to find out more about our propellant mixing, you can find that here.
Backboard Test
Now that we knew our mixture would ignite, and that our basic safety procedure would work, we decided to roll out the first completed part of the test stand, a backboard. This backboard, would let us characterize the shape of the flame to a better degree. It would have an easily visible grid pattern drawn on it so that more accurate measurements would be able to be taken. Additionally it would provide a steady background allowing for more consistent photos.
Backboard Design
The backboard was ∼2.5 by ∼6.25 feet (∼ 72 by ∼180 cm) and was partitioned into 30 grid spaces measuring ∼10 by ∼7.5 in(∼24 by ∼18 cm) (Note: I wrote down the exact dimensions somewhere but I can’t find it so if there is a tilde ∼ before a number in this post it means it was pulled from my memory). The backboard was made out of a sheet of plywood supported by two cardboard mailing tubes. The plywood was tied to the mailing tubes using nylon rope. The cardboard tubes were clamped to two homemade saw horses to allow it to stand vertically. The horizontal lines were drawn with magic marker, while the vertical lines were made using electrical tape. As you can see in the photo to the right, the backboard’s bottom is not flush with the ground. This is because the test stand will be about that tall once completed.
Note: All materials used in the construction of the backboard, aside from the electrical tape and nylon, are easily flammable. This was not a good choice of materials. These choices were made because non flammable materials to replicate the design would have been prohibitively expensive at the time. We made sure to have an additional type ABC fire extinguisher on hand during this test to mitigate any increased fire risk.
Backboard Setup
For this test, because the test stand was not yet complete, the motor was again buried in the ground. The backboard was setup six feet away from motor and tilted towards where I had taken photos during the last test burn.
To the right we can see a comparison between the picture we get from the test burn with the backboard and one from the smoke test. Because the relative position of me to the motors was unknown, I scaled the two flames until the Ski helmet that we were using as a GoPro mount were about the same size.
Backboard Conclusion
After this test we decided to retire this backboard permanently. The added fire risks were too great to continue to use it during future tests. Our first few in-house motors were quite simple and conservative in design, but as we experiment with different mixtures, ensuring the backboard wouldn’t catch fire would have presented one of the first limits to what we could do. For example, if we wanted to add in more aluminium powder to the mixture, we wouldn’t be able to, as there is going to be a greater chance of the motor throwing off burning aluminum particles which could ignite the backboard. I felt it was important to include this test as part of the rollout series to show someone who may be new to rocketry to know that failures do occur. It would have been easy to just skip over this test, as the back board wont appear in any future tests, and pretend like it didn’t happen but that wouldn’t have been realistic. Stuff happens, things don’t always go the way you expect, and adapting is a normal part of the process. Additionally just because this backboard didn’t work out doesn’t mean that we wont have another, more suitable backboard in the future. The lessons learned from this test will inform and guide the design of any future backboards we build.
Note: We ran this test 2017-03-10 (YYYY-MM-dd as all dates should be formatted).