All custom Carbon L3 build for less than half the cost of a Wildman Mach 2

[Brainstormz123]

Gonna be posting a "build thread" on my L3 rocket that I am most of the way complete with building

 

[Brainstormz123]

I began by printing a male mold for my nosecone. I then filled the parts with a microballoon and epoxy mixture and sanded it down to be smooth:


As a mold release on this part, I used an extra large condom placed on top of the part (purchased from a company called luckybloke) and then did the layup with 2 layers of carbon sleeve (the picture is fiberglass so you can get a better idea):


Here it is with dry carbon on top as well


I did the layup using US Composites 3:1 epoxy on two layers of carbon sleeve from Soller Composites, and then trimmed the tip off and excess off the bottom, then hit the mold with a hammer and it released, leaving me with a nosecone:

 

[Brainstormz123]

The next part that I went to make were the fins. I took the shape and lasercut the it on my school's laser cutter out of 3/16 plywood.


I then cut out 1 layer of carbon and 1 layer of red carbon kevlar to skin these fins with (I didn't take pictures of this, my apologies). My process for making these is to place the cloth on top, wet it out with a brush, then really rub in the epoxy with a plastic card (used gift card in my case). I did one side at a time and left a little bit of excess around the edges for me to sand off.


After doing both sides, I ended up doing a resin wash over the fins in order to make them look shinier and smoother:


After that, I sanded the fins to 600 grit and they are now super shiny when wet, so a clear coat at the end will make them look very nice:

 

[Brainstormz123]

The next step was making the tubes. I don't have a bunch of space in my apartment, so I did all of the layups in my bathroom, sorry for the very odd photographs . I acquired some "mandrels" which were 4in cardboard tubes I wrapped with a layer of mylar to release. I didn't get a picture of the mylar, but I wrapped it around 1.5 times very tight and taped it to itself, not to the mandrel. This helps make everything release very easily.

Here is one of the tubes in my bathroom during the layup, I did 3 roll wrapped layers and 1 final sleeve layer to remove the seam. I didnt put anything to increase the surface finish as I planned to sand and fill the tubes and paint on top at the end.


And here is the other tube:


Here is a picture of the two tubes after I trimmed them:One of the tubes is much thinner because I went without the roll wrapped layer, and I ended up doing 2 more layers on top of it to match the OD of the first.

 

[Brainstormz123]

I unfortunately did not get any pictures of this step, but to make the coupler I took my cardboard mandrel, cut a slit out of it, and glued it back together to make it the right OD. Then I did a layer of mylar on top of that, and roll wrapped 3 layers of carbon to make one long coupler which I will cut up soon.


The final tube part I have made so far is the motor mount tube. The roll my composite material came in was a thin 3in ID cardboard tube, so I just did one layer of carbon on top of it for fun (really not necessary but why not:

 

[Brainstormz123]

Then I cut fin slots in one of the carbon tubes. After deciding what tool to use, I choose probably the objectively wrong one, the angle grinder. Here are pictures of the slots right after I cut them. I cut the remaining tabs off with pliers after. They don't suck, but I don't like that there was skill required to get them straight and I'll figure out some other technique later. I dont fly many non min-diameter or submin flights often, so fin slots are something I dont do much:


I also printed out centering rings to align the fins as well so I don't need a fin alignment jig (I still cut one to put on the outside anyways):

 

[Brainstormz123]

For funsies, I just stacked up the rocket to see what it will look like, and dang it is tall.

From where I left off, I first epoxied one centering ring onto the motor mount tube:

 

[Brainstormz123]

After this, I put the motor mount tube into the airframe, put the rear centering ring on, and used an external laser cut fin alignment jig, and then tacked the fin into place (do not have a picture of this step). I then removed the motor mount tube and fin assembly and began on my internal fillets on the fins to the motor mount tube. I also mounted my shock cord on this step:


After those fillets cured, I put the fin and motor mount assembly back into the airframe tube through the fin slots, and then did external fillets:



After this, I epoxied the rear centering ring into place (I think this is a step that I did in the wrong order, more info to come later)Finally, what was remaining was the electronics bay, so I laser cut some bulkheads (two per side) and glued them together to form my "stepped" bulkheads. I ran a single threaded rod through the av bay coupler and used eye nuts on the ends as recovery attachment points and to add compression to the section. Here is a picture of my printed AV bay, I'll get more pictures of that setup later if you desire:

 

[Brainstormz123]

To test fly this rocket, I needed a motor, so I made an EX J500 with PropX in an aerotech 2 grain 54mm single use EMK. I also glued on some rings as my motor adapter to make it a "75mm" motor:


I then did some copper tape antennas onto the switchband section so that I could have tracking and telemetry during the test flight. The only picture I have of this process is post-recovery, but it was done by placing kapton tape on the airframe, copper tape a bit longer than 1/4 wavelength, soldering an SMA cable to that tape, and then using a VNA to tune the antenna to my desired frequency by cutting it shorter and shorter:


After this, I headed out to FAR to launch, installed rail buttons with a screw and nut on the other side, and beyond that, integration went smoothly, and I was on the rail ready to launch at 7:30 am (30 minutes before the waiver even opened ):

 

[Brainstormz123]

Here is when things went less than ideal, I have attached the launch video, but you can see it did a little spiral while the motor was burning. However, recovery all performed nominally, and it reached an apogee of 2970ft (or 2971/2969) if you ask the other two computers I flew (AV bay included two stratologgers, one custom for datalogging and tracking, one RF beacon for tracking).

View attachment IMG_8279 (1).MOV

The rocket was easy to track as I had data transmission the entire time and had my handheld directional beacon tracking setup which I used to lead me directly to the rocket:



Recovery was a success, however my drogue chute was slightly oversized and the winds this day were about 20mph on the ground, but over 70mph at 3000ft. The rocket landed around 2500ft away from the launch rail.



After looking at the rocket to try to figure out why it spun, I first thought somehow I might have misaligned the fins, but they were all straight as an arrow and 90 degrees apart. Then I looked at the motor mount tube, and sure enough, it wasn't straight . I think the step above where I mentioned I did this in the wrong order is to blame as I should have put the rear centering ring on while I did the external fillets. It was pretty clearly not straight and I am not confident in this section's ability to handle the M1780 I have for my certification flight.

My next steps are probably going to be to remake the fin section with the upper body tube, and make a new upper body tube to replace that one (probably a shorter body tube, this rocket doesn't need to be as long as it is). I will still be shooting for a launch on February 24th at MDARS, but I may need to push that to the March launch date if I am not ready in time.

 

[Brainstormz123]

Overall, the cost of this rocket was around $50 worth of materials, all of which I already had and didn't purchase anything new for it. This is my second ever through the wall finned rocket (even though ive done a ton of submin and min diameter flights) so I apparently had a lot of learning to do regarding "lower performance" rockets

 

[Flare]

Nice thread and documentation. More people really should be doing their own composite tubes from scratch. It's so much cheaper than buying from a supplier and it's far easier than you might think.

 

[tsbooska]

Very nice thread Mr. 123! Look forward to seeing the L3 flight!