1 week ago


So how do we go about

So how do we go about stabilizing the ‘rocket’? We simply need to glue or tape a stick to it. This will push its CP downwards away from the CG. Tape or glue a thin dowel stick or skewer stick to the body using masking tape or a glue gun. Balance the rocket at point A (Figure 9.10) with a pen held horizontally. Correct the balance by glueing another piece to the skewer stick or cutting a piece from it. B. Igniting the rocket - finding a fuse In many states in Australia and the USA, the making and possession of igniter fuse by unlicensed citizens is illegal. So once again we have to find a creative alternative: • You can make a simple electric igniter using nichrome wire, copper and flex wire and a 9V battery (Figure 9.12), or • buy commercial model rocketry igniters from a hobby shop, or • if you have pyrotechnic fuse - by all means use it. Fold one end of the fuse back before inserting it so it forms a hook to prevent it from sliding out. Don’t skimp on the length of the fuse. • But there is an easier way. Off to the party shop this time . . . and buy a few packs of sparklers. (They’re not banned!) Cut the bare metal wire (handle) from the sparkler with a pair of pliers. You will be left with the grey pyro part which is tapered on one end. This thinner section can easily be inserted into the rocket nozzle and will “auto-grip” in a 3.5 mm hole (Figure 11). On ignition, the gases will simply expel the sparkler from the nozzle hole. Figure 9.11 Sparkler as fuse Figure 9.12 103

Safety / Risk Assessment ! Never launch a rocket closer than 500m from power lines, hay stacks or a thatched roof house ! Do not launch in a built-up area - the rocket has no parachute ! If you are close to an airport then you may have to get permission to launch. Check your local council regulations ! Rockets should only be launched vertically ! Do not launch even if a mild risk of bushfire exists or if the wind is blowing ! Spectators should be at least 10 m off and you have to step back 5 m after igniting the fuse ! When you have a failed launch, wait at least 1 minute before approaching the rocket ! Always wear eye protection C. The launch A thin metal tube is planted upright at the launching site. The rocket’s thin dowel stick should slide loosely into this tube. Insert the sparkler into the rocket engine hollow core as far as it will go. It should stay into position itself. Check that all is in sync with the safety regulations, light the sparkler and step back 5 metres 5 ... 4 ... 3 ... 2 ... 1 ... launch! The rocket produces copious amounts of smoke leaving a visible trail (Figure 9.13). Figure 9.13: A static rocket motor test Disposal Retrieve the burnt-out rocket body and discard it in a bin when cooled down. The propellant mix can be safely stored for months as both 104