Design Notes
Project history
This project was born in June 2020 in the early days of the Covid pandemic. It is dedicated to my children, educators teaching through the pandemic, and NASA’s Perseverance mission team, all of who reminded us to dare mighty things even when the future is uncertain.
Acknowledgments
This launcher design borrows heavily from existing designs shared by the international water rocket community, especially Air Command Rockets, US Water Rockets, and Raketfued Rockets. It draws on the insight and testing of dozens of people who provided feedback via comments, shared Makes, and e-mail correspondence. Some of the ideas presented here are original, but the vast majority are not. I apologize in advance as my in-line credits are certainly incomplete.
System Design
This launcher must be intuitive, robust, modular, portable, and globally accessible. These five principles lead to design decisions that give its form and function. Why clamps? Why a full-bore nozzle? Why eliminate adhesives and make PVC pipe optional? Why have removable Cores?
Cores
The Core subassembly slides into the bottle to form the pressure envelope. It was the most challenging aspect of launcher design and has undergone four iterations to be fully adhesive-free and globally-compatible. Follow the path from brass fittings to PVC cement to press-fit, stress-tested past 100psi/6.3bar. Go deeper into specific Core designs.
Base
The Base subassembly anchors the Core and rocket to the ground and provides triggered release. Tested over three years in various geometries, Clamp shapes, Leg types, pipe compatibilities, and anchorings. Strengthened from breaking itself on launch to surviving an 80kg dynamic load. Functional considerations drive every aspect of the launcher's distinctive shape.
Pressure and Safety
Pressurized systems are inherently dangerous. While personal responsibility is critical and I make no warranties about the appropriateness of this design or validity of any of these analyses, it remains that I want to make this design as safe as possible. Understand how this system can fail and plan safety precautions.
Rocket Stability
"How high does it go?" is the most frequently asked question about the launcher. But the answer has less to do with the launcher than with the rocket. Does it go straight or does it tumble? Learn the very basics of rocket aerodynamics as it applies to design and use of fins and payloads, with links to primers.
Fins
Push your Center of Pressure toward the tail. Do it within the limitations of 3D printing and launcher geometry. Try to make it not break the first time it hits something. Maybe try to make it fit on every single bottle and aim for an aesthetic that doesn't look like a bomb.
Payloads (under construction)
Push your Center of Mass toward the nose. And maybe slap some useful things on there, like a parachute. Maybe an altimeter? A camera would be great. Maybe it could be modular and you could swap modules in and out, or at least save most of the rocket when the parachute doesn't deploy and the payload section smashes to bits?
Under construction until I get back around to it.
Future: On PET Bottle Neck Finishes
More than you ever wanted to know or thought to ask about polyethylene terephthalate carbonated soda drink bottle neck finishes. An accumulated lay understanding of an under-appreciated geometry as it pertains to clamping rockets and maintaining pressure.