Since this project is actually dealing with rocket science, at least in the background, it's not too hard to imagine that in this kind of a DIY project, some elements will not be DIY. (Apologies to the would-be model rocket enthusiasts who thought they were actually going to build their own rocket engines!) This guide will take you on the road to building your own rocket, just not the engine or the detonator. First, you will need to purchase a set of engines and detonators (they usually, and thankfully, come together in the same package). The secret language of the letters and numbers on the engines will be explained later. Hint: purchase an initial set of engines that begin with the letter B. While you're at it, why not make a little investment in recovery wading (see below, below), even though there are DIY substitutes for this commercially produced product.
At this juncture, it is important to acknowledge a debt of gratitude to the real rocket scientists behind the commercially produced rocket engines and detonators. Without them, model + rocketry would not exist. The model engine production safety regulations alone would fill an entire book, and the process of making model rocket engines is way too dangerous.
As noted by the Stine family members in their ultimate guide to the hobby: "There is no safe way to make a rocket motor of any type. This is a statement of fact, not a matter of opinion... A model rocket motor... is a factory-made device that is subject to rigid quality standards, quality controls, and statistical batch sampling and testing procedures. It's very reliable and will do exactly what it's designed to do. You, as a model rocketeer, don't have to handle dangerous chemicals, worry about whether the motor will have proper thrust, or take extensive and expensive safety precautions" (p. 65).
While different materials can be used, recovery wadding is an essential ingredient for any rocket building project, unless you are planning to build a "trophy" rocket that simply lives in a display case, never to leave the surface of the earth. Using a few scraps of wadding will reduce the potential that your rocket will catch fire during the secondary explosive charge phase. While a few pieces of household insulation may be used in place of this recovery wadding product, you should carefully handle the insulation with gloves, and discard after use.
The rocket engine needs a secure place to live inside your rocket. After all, you don't want the engine to fall out of your rocket! If the picture below seems to have gone a little too far too fast, please remember that the best way to get started is to jump right in! Now, lets walk through the steps in getting the engine housing up and ready.
Begin by cutting the used toilet paper roll lengthwise, all the way. Because the standard rocket engine (there are smaller and larger engines) has a length of 2.75 inches you will not need the entire length of the toilet paper roll. You need only work with a toilet paper roll length of 3.5 inches. An engine housing that is 3.5 inches in length will allow your engine to protrude from the base of the housing by a quarter of an inch and leave enough room at the top of the housing to guide the secondary charge in a vertical direction.
Tightly roll the engine housing around one of the rocket engine (that you purchased). As you roll along, use glue-stick glue to glue the cardboard toilet paper roll engine housing to itself. (You will not likely need the entire width of the toilet paper roll either.) Once you have complete the gluing process, right up to the edge of the engine housing light cardboard, wrap the engine housing tightly with elastic bands. Allow the gluing process to dry completely, keeping the purchased engine inside of the housing, as depicted above.
While the glue holding your engine housing in place is drying, it is time to prepare the way for connecting the housing to the fuselage.
From left to right:
Cut strips of thin cardboard (use a cereal box, for example) These can be cut the length of a cereal box, and a quarter inch wide. Pictured in the center panel is the engine housing that is ready to be attached inside of the fuselage. Select a fuselage, made of sturdy cardboard. Cardboard used in the construction of most toilet paper rolls and even paper towels is too thin and flimsy. The fuselage shown on the right is taken from a used saran wrap roll. This cardboard is much sturdier, and perfect for use as the body tube of a model rocket.
It is highly unlikely that the fuselage will have the same diameter as the engine housing. For the rocket to operate properly the housing must be able to fit inside of the fuselage.
Use glue-stick glue to glue the spacer cereal box strips to the engine housing. Begin by setting the lower part of the first strip 1 inch or 1.25 inches above the base of the engine housing, as depicted in the center pane. This whole process takes a bit of time as the glue should partially dry before the next strip is applied. To create a snug fit, add a few more inches of spacer strip to the engine housing than are needed. Wait for the glue to dry and carefully peel back (by the inch or two) some of the spacer strip material until a snug fit within the fuselage is created. This is a process of trial and error. If the engine housing will not fit snuggly in the fuselage, peel back some of the stripping and repeat, if necessary. (Or add a few inches as the case may be.) Be forewarned that this operation may provoke a few curse words!
Once there is a snug fit, prepare to glue the engine housing to the inside of the fuselage. Using wood glue (not glue-stick glue), run a bead of glue around the interior circumference of the fuselage beginning about half an inch up from the base of the fuselage. Slide the snuggly fitted engine housing into the fuselage, moving the engine housing up so that you leave at least three quarters of an inch between the base of the cereal box strips and the base of the fuselage. This way, the engine housing itself (not the cereal box strips) should extend out past the base of the fuselage by a quarter of an inch.
These three photo panes depict the process. On the left, the engine housing is ready to be glued into the fuselage. In the center, the placement of the engine housing inside the fuselage is complete. The three quarters of an inch space mentioned above is useful because it provides greater flexibility in fin construction and it paves the way for the future consideration of adding a second (booster) stage to the model rocket. Finally, the right hand pane shows the inverted engine housing inside of the inverted fuselage, together with a standard rocket engine inside of the housing.