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ExposeExciteIgniteMay2012

• Remove the dowel

• Remove the dowel slowly from the tube so the putty doesn’t get pulled along. Finish off the outside putty with a wet finger or dowel. Leave to cure for 30 minutes. Alternatively you can simply ram dry bentonite clay or two sheets of toilet paper (yes, it works!) down the tube with the dowel and hammer. Do this on a solid concrete floor. Use the same procedure as we will use to load the propellant - see next pages. The plug should be ! 5 mm (0.2”) thick. • Mark this plug with a “T” (for “Top”) on the body tube. 2. How to Prepare and Compact the Propellant Figure 9.5 We will prepare a rocket using "classic" sugar-based rocket propellant comprising of a mixture of potassium nitrate (KNO3, saltpetre) serving as the oxidizer, and sucrose (C12H22O11, icing/confectioners sugar) serving as the fuel and binder. Although not a high-performance propellant, its main advantage is the relative ease and safety of preparation and common availability of the ingredients. Icing sugar contains a low percentage of corn starch (C6H10O5)n but this is acceptable as it is chemically very similar to sucrose. Granular or table sugar may be used also but asks for some rigorous grinding. The particle sizes of both chemicals are very important as these determine the impulse and burning rate and thus the success of your project. I have found invariably that icing sugar particles are fine enough but the saltpetre usually requires some grinding. a. Preparing the chemicals: Grind the saltpetre (about 25 g) in two batches in a mortar & pestle. Another way of doing this is to use an empty wine bottle and grind a small quantity at a time with a rolling action on a clean, solid surface 99

for two minutes. The finer you can get this, the better the burning rate will be and the higher the impulse. An electric coffee or herb grinder will do the job too in less time with less human effort! Do not use your kitchen grinder - for a few dollars one of these makes a great investment for the lab (Figure 9.6). b. Do the same with the sugar (15 g) if it is not in a very fine form. Safety: Do not use the same grinder as used for the saltpetre. In pyrotechnics the rule of survival is: Never grind oxidant and fuel together. c. We will use a ratio of 65% KNO3 and 35% Sucrose, a mix ratio favoured by many beginner rocketeers. Each rocket will require around 10 g propellant. So I would suggest a mix of 30 grams to start with for making 2 rockets. Thus, at the above ratio you will require: KNO3 19.5 g Sucrose 10.5 g Weigh these amounts on an accurate scale into two separate plastic cups. d. Blending the two components: Transfer the weighed components to a plastic container, seal and shake for two minutes. Complete mixing of the components is necessary for optimum and consistent performance. Adding two glass marbles will enhance the mixing and perform further pulverising. Always keep the lid of the container sealed as the propellant is slightly hygroscopic and will absorb air moisture. Safety: Once combined, the two components form a flame- and spark sensitive propellant but is not impact sensitive. So shaking it holds no danger, but be sensible and keep it away from any possible ignition source. (Try this: Wear safety equipment and place a small quantity of the blended propellant on a solid surface and hit it with a heavy hammer - no reaction. Now strike a match and ignite the mix). e. Loading the propellant: Use another sheet of paper to prepare a small powder scoop as in Figure 9.7: Figure 9.6 100