Monday, August 14, 2006

Molten parachute

Well, mid-afternoon on Sunday the weather cleared up long enough for us all to head down to Midsummer Common and launch our rockets. We had two to launch: Mike's, and mine. A couple of other folks from the lab turned up to help, including our 'propulsion expert', Henry.

After improvising some drinking straws and a few wooden skewers into a 'launch pad', assembling the motors into the rockets and doing some final assembly, we proceeded to launch Mike's rocket, 'Colin 1'. He'd designed his to be very minimalistic: without any sort of recovery mechanism, it consisted of nothing more than a paper tube with fins, a rocket motor and an acrylic plug for the nosecone. Nevertheless, it performed well: on ignition, it went straight up and disappeared. We never saw it again! We think it might have landed in the grounds of Jesus College, judging by the wind. We'd gathered quite a few onlookers by this point, and we think they were quite amused.

My (unnamed) rocket was next: as I mentioned, I'd fitted mine with a parachute (improvised from a freezer bag). Unfortunately, I'd forgotten anything to use as wadding to put in front of the ejection charge and drive the parachute and nosecone out, so I made do with just some random piece of paper, crumpled up.

The actual launch exposed some shortcomings with my design: firstly, the glue was plenty strong enough to hold my fins on. Unfortunately, the paper I'd made the fuselage out of wasn't! My rocket lost three fins, and thus tumbled out of control after the motor had burnt out rather than following a parabolic trajectory. Secondly, the parachute wasn't attached correctly. Rather than having a piece of elastic from the fuselage to the nosecone, and then a long thread from the nosecone to the parachute, I should have had a long thread attached to a piece of elastic connecting the nosecone to the fuselage, and then a short thread onward to the parachute. As it was, the parachute just sat in the fuselage and melted in the hot gas from the ejection charge, rather than deploying.

The plan for next week is to build a two-stage rocket (a D-12-0 motor for the first stage and some variety of B engine for the second stage). We're also hoping to launch another couple of small rockets as well, if we get the time to make them. The problem is that the two-stage rocket is going to go much higher and is going to be quite a bit bigger, so we won't be able to launch from Midsummer Common this time: we're going to need to find an out-of-town launch site. Since both the people with cars are away this weekend, that could be something of a mission.

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