Scratch Build L1

[kavy8]

While I’m wrapping up my third year on my uni rocket team, I am aiming for my L1 in late April (we’re gonna pretend the launch isn’t 3 days before my last final exam, and the day after another final). I got everything in earlier this week and briefly started, but I wanted to make a build thread as well.

I ordered 2 kits and a bunch of other parts for others members on my uni rocket team, and this was everything out of the box! 3 of us are doing scratch built 4” diameter with 38mm motor mounts, hence the duplicated parts.

I got started by finalizing the physical dimensions of the body tube and MMT, and then modelled a fin slot cutout jig and a fin alignment jig, which were then 3D printed on Tuesday. I marked out the slots, removed the cutout jig and then cut out the slots. They weren’t the prettiest cuts cuz I didn’t have a fresh blade, but the fins ended up fitting nice and tight later on


After cutting the slots, I got a 2’x2’ sheet of birch plywood from home depot for the fins and centering rings. I got them laser cut at the uni, and the second I got home yesterday I went to dry fit everything instead of working on my senior capstone project, because this is way more fun. I dry fit the fins with the motor tube and my 3D printed alignment jig, and everything seems to fit really nice!




I took the aft centering ring out just for the last photo, but it also fit snugly. Will need a bit of light sanding on the OD to slide through the tube a bit easier, but turned out decently.

I’m hoping to make slow but steady progress on this, life is crazy busy rn with my last month of undergrad AND pushing for our hybrid to be ready to start doing cold flow tests and mock launches, while I’m also rebuilding a motorcycle, but I’m sure I’ll squeeze in time to make it for the April Launch

 

[jmasterj]

Those fins are pretty small, have you sim'd this design in OpenRocket yet?

 

[kavy8]

Those fins are pretty small, have you sim'd this design in OpenRocket yet?

Yeah, I started in OpenRocket. I know they look small, I am planning on adding 150-250g of nose weight and I went with 4 fins as well. I plan on only flying H's and Baby I's. I did my best to position everything as realistic as I expect it to be in OR, with mass overridden values for everything, and on a baby I, I get a stability of around 1.5. With the H I plan to use for L1 I get about 2 cal stability

 

[jmasterj]

Yeah, I started in OpenRocket. I know they look small, I am planning on adding 150-250g of nose weight and I went with 4 fins as well. I plan on only flying H's and Baby I's. I did my best to position everything as realistic as I expect it to be in OR, with mass overridden values for everything, and on a baby I, I get a stability of around 1.5. With the H I plan to use for L1 I get about 2 cal stability

Fair enough. Any particular reason you went with the smaller fins + nose weight, instead of using larger fins? Aesthetics?

 

[kavy8]

Fair enough. Any particular reason you went with the smaller fins + nose weight, instead of using larger fins? Aesthetics?

I wanted to sweep the trailing edge forward and minimize the height of the fins so that they’re less likely to be the first thing to impact the ground on landing, and lower the chance of them snapping off since that seemed to be the number 1 reason for failed certs at the launches I’ve been to. That logic may be totally flawed though, I wouldn’t be surprised haha. I know that adding weight to compensate for small fins brings it down faster under chute, which also increase the risk of snapping fins, but I’m hoping the pros and cons swing in my favour