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Ready to Rocket?

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Recently we looked at how model rockets work and what’s involved in flying them. But the real fun is in building your very own model rocket from a kit. Starting with a basic kit is an excellent idea as the building methods you learn and use will also apply to bigger kits or to designing scratch-built models.

The rocket kit we have chosen is the Estes “Green Eggs”. This is a reasonably large model rocket as it is designed to launch with an egg in the payload bay. Egg lofting in rocketry is a fun competition in which the egg has to survive the journey for the flight to count.

The kit arrives in a plastic bag. Take care not to crush or press on the contents as you can easily bend or kink tubes and components. Inside the package are numerous tubes, some balsa fins that are pre-cut but still held in a sheet, and a plastic nose cone with an extra section that acts as a coupler. Finally, there is a smaller sealed plastic bag, some decals/stickers, and a set of instructions. It’s worth reading through the instructions a couple of times and identifying all the pieces before actually starting to glue anything together. White PVA or other white wood glue is a good option. You’ll need a sharp craft knife and a surface that is okay to cut on. You’ll also need scissors, a ruler, a pencil, fine sandpaper, and painter’s tape.

The instructions begin with building the motor mount tube, centering rings, and the motor clip retainer system. We start by marking 3 lines on the motor tube at 12mm, 25mm, and 52mm marks from one end. (Dimensions will differ for each manufacturer’s kit.) At the 52mm mark, we make a small cut around 3mm in length. This cut is for the right-angled section of the motor clip to push through into the motor tube slightly. The metal bit sticks into the inside and you then glue in the motor block ring pushing it into the motor tube above the little metal clip. The combination of the green motor block ring and the end of the metal clip forms a solid area that the motor will press against transferring the thrust into the rocket.

We then glue the thin black card ring over the metal clip aligned with the 25mm mark, and finally, we glue the two centering rings onto the 12 and 52 mm marks. It’s worth taking your time and using a ruler to make sure that both your centering rings are nice and straight and an equal distance from the ends of the tubes all the way around.

While the motor mount assembly is drying you can use a sharp craft knife to carefully remove the fins from the balsa sheet. They are cut out already but have small tags holding them in place. Once they are removed you can give them a very light sanding all over and then use your sandpaper to make the leading edges round. Even though this model won’t be a super high-performance rocket compared to smaller and sleeker builds, it will fly higher if you round the fin edges to reduce the drag and make it more aerodynamic.

Before you assemble the fins, motor mount assembly, and body tube, there is another little task needed to mark out a line on the tube. According to the instructions, carefully use the frame of a door in your house, hold the body tube against it, and then mark a central line vertically along the tube. This method works perfectly. If you have something else that is a long right angle, such as a length of angled metal, you can use that to create your line. The line you create should be between two fin slots and later we will use the line to align a small launch lug tube.

With the Green Eggs model, we have to fit the motor mount and then glue the fins through the slots to the outside of the body tube with the inner edge of the fin glued to the motor tube. This is called “Through Fin” design and makes for a very strong fin and motor mount area. Other kits instruct you to simply glue the fins glue to the outside of the rocket, While this method may be less strong, it is slightly lighter, so both designs have their uses.

To glue in the motor mount we need to make sure there’s a good helping of glue sealing the forward centering ring into position. When the motor mount is in position, in this particular kit, the end of the motor tube is level with the end of the body tube so you can work out where the forward centering ring would sit. Having worked out that distance, a good tip is to mark a stick or a straw that you can use to apply the glue at the correct depth for where you want to place the glue in the tube. Apply a ring of glue and then partially insert the motor mount assembly. Once the forward ring is past where the rear ring will eventually sit in the body tube, you can add some glue for the rear ring and then push it all into place. Note that you must not have the motor clip under a fin slot or you won’t be able to push a fin into place.

With the motor mount assembly in place, you can now fit the fins. Place some glue on the inside edges of the fin and press it gently through the slot in the body tube. Then add glue to the outside edges of the fin, smoothing the glue into a neat fillet with your finger. Repeat this for all fins. When all the fins are fitted, but not dry, place the rocket and fins over the fin alignment guide image in the instructions and make sure that everything is neatly aligned. A wonky fin won’t help your rocket fly.

Next, let’s separate the nose cone and the payload shoulder section. These are supplied as one piece and you cut in the groove to separate them. Experience teaches that the easiest, neatest way is to do a lot of light cutting, running a craft knife gently around this seam a lot of times until it separates. Once separate, you can test fit the pieces together. The nose cone and shoulder entering the plastic payload tube need to be quite secure, but also removable for you to have access. You can use pieces of painter’s tape on these sections to make them a tight fit. Where the shoulder sits inside the body tube should not be too tight or too loose as it needs to be blown out when the parachute ejects. We found we didn’t need any tape and it was perfect as it came.

Next, cut out the shock cord mount from the instructions, or make a copy of it on some paper and cut that out. The upper payload and nose cone assembly will be attached by a length of elastic. The paper is folded and glued over the elastic with a lot of glue to soak into the paper. With the folds completed, the paper anchor section is glued into the inside of the body tube. Two things are important here; the anchor needs to be well below where the shoulder will be when the payload is inserted and the anchor needs to be smoothly pressed against the inside of the tube to make sure it doesn’t snag the parachute.

At the other end of the elastic, you tie a knot to fix the elastic to the payload area coupler and then you attach the parachute to this point, also. To attach the parachute you gather all the shroud lines, push them through, and make a loop with the 3 shroud line ends. You then bring the entire parachute through the loop and pull it tight. This type of knot is called a “larks head”.

Finally, you need to glue on the launch lug. This small tube will act as a guide on the launch rail so it must be put on nice and straight. Take your time aligning it with the line we drew earlier. Once everything is dry you can paint your rocket. Painting adds weight so you want to add thin amounts and make the finish as smooth as possible. The best method is spray paint, but this can be difficult if you don’t have nice weather or an outside space. It’s perfectly fine to hand-paint your rocket with a brush. Some people even choose to fly their rocket without paint to make sure it flies well. If it does, then it’s earned its paint!