Project
207 Box rocket flight.

Pre-flight Analysis

• I started out this project with the goal of finding a material that I could use to make the rocket body, fins and nosecone out of. The material needed to be lightweight, inexpensive, rigid and easy to machine. What I settled on was a composite material comprised of two sheets of single ply matt board with a sheet of Foamcore glued in between. The Foamcore by itself is rigid but not very strong. Adding the matt board, which is very strong but too flexible by itself, created a material that was rigid and strong, yet lightweight and easy to machine. 36x48" sheets allowed almost any size structure to be built. The main drawback to this composite is that it's flat and would not be condusive to a round rocket body or nosecone. So allowing the material to dictate the shape of the rocket, I found myself building a square rocket. When I looked at the size square needed to hold 4 engines I was surprised to find that the total frontal area was less than the round shape used to hold 4 engines in the 117 flight. The square rocket was easy to construct and took less time overall than the previous round rockets.
• This project had a minimal amount of metal elements used in it's construction, the majority of parts being wood, plastic or paper. This cut down on the body weight. Eventually I would like to have a non-recoverable booster section that at apogee would fall away leaving the payload section to return under parachute. Since the booster section would be made of materials like paper and balsa, it's ballistic return to the ground would not be a large concern.
• This rocket has 4 engines identical to the Pourstone nozzle engines tested on 124 which worked fine. The recovery device will be activated by a 20 second time delay fuse. Smoke tracer rods were attached near the nozzles. Hopefully the hot exhaust gasses will ignite these during flight. There are no electronics, other than ignition wires, in this rocket.

Post-flight Analysis

• Lots of problems with this rocket. The engines didn't ignite at the same time causing the rocket to be off balance. Then, soon after the rocket left the rail, the engines exploded. Since the 920 static tests, I have been observing a pressure spike towards the end of the engine burn. Sometimes this spike causes the PVC to fail and sometimes it sends chunks of burning propellant out the nozzle. It seems that the fuel is cracking towards the end of the burn when the fuel is thin causing an unrestricted burn in the engine. This has never happened before and the only thing I can think of is that the PVC is expanding under pressure causing the propellant to crack. I have no explanation as to why this has not been a problem over the past five years and is just now starting to cause failures.
• The paper composite structure of the rocket caught fire very easily and was not as strong as expected. Still, it was a good experiment.

Construction

• The rocket body, fins and nosecone were made from a paper composite consisting of a sheet of1/8" Foamcore sandwiched in between two pieces of single ply matt board. The entire structure was epoxied together.

Pros

• Easy to construct.
• Inexpensive.

Cons

• Flammable.
• Weak under high stress loads.
• Engines need work.

Pictures

Video

• Flight 01
• Static 01 gauge
• Static 02 gauge
• Static 03 gauge

Drawings

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