18mm C-Class Model Rocket (BYO 29mm Tube)

My goal was to have low-power rocket kits that were stable and safe to fly, but also easy to assemble by tiny hands in minimal time without the need for glue or too much precision.

This print file includes a friction fit fin can, fins and nosecone that are designed to be as easy to assemble as possible. The nosecone is two parts that thread together for easy of disassembly if cords need to be replaced.

It takes 18mm A/B/C class motors, and flies to 120/300/600 feet accordingly. It is stable in flight under these motors with between 1.5 and 2.5 CALS (see attached Open Rocket screenshot), but larger reloadable aerotech style casings are fly at your own risk in regards to stability.

You'll need:
1x 29mm body/motor tube like the one linked below
1x parachute/streamer for recovery, but any sort of plastic or mylar film will work for a streamer.
8ft or 2m of shock cord with some sort of fire-resistant material in it like elastic or nylon that won't melt right through.

Instructions -
1) thread both ends of a 30cm or 1ft section of cord through the two holes in the motor mount from top to bottom in a U shape, and tie knots at the base (boom boom end) to keep it from pulling through.

2) Fasten the rest of the cord to the loop, and run it through the body tube.

3) Press fit the body tube down into the motor mount assembly. Friction is sufficient here to keep the rocket assembled in flight, but if you're worried about it a little glue could be spread into the motor mount before assembly.

4) Tie the parachute towards the top of the cord, and tie the cord off to the nosecone base.

5) Press-fit the three fins into the fin slots. They should be a tight friction fit, you might need to trim up any elephant's foot first layer issues.

6) Screw on the nosecone top, stuff some wadding/insulation down the body tube, insert the nosecone and you're ready to fly!

Body Tube: https://www.apogeerockets.com/Building_Supplies/Body_Tubes/Low_Power_Tubes/29mm_x_13_Body_Tube_Holds_FG_Engines

Edits: After a few flights, I've updated the mounts to loosen the launch lugs, include a lug on the nosecone, and added an internal fillet to the motor block to prevent blow-out during thrust. Also, I suggest a small dab of superglue in the fin slots before flight, they can dislodge on landing.

Current flight record is 533ft, carrying a jolly logic A3 altimeter in the nosecone.

Print instructions

Everything is printable without supports, I printed at 2 walls and 15% gyroid infill. The print walls are thin enough there is very little actual infill aside from the nose cone. Print the motor mount with the larger concentric circles down, no supports, as long as your machine can handle 45 degree overhangs this should be fine.