A Homemade Rocket
- a tube (for engines A-C a class 125 1/2" PVC pipe. for size D engines 3/4" class 125 PVC pipe) These can be purchased at any hardware store.
- cardboard: to cut out the fins
- Glue (I recommend using a hot melt glue gun)
- model rocket engine
Total cost: Home built rocket+engine=$ 2.50
Store bought Rocket + C engine $15.00
Building your own rocket is the economical choice and the PVC is strong enough to be used many times.
Building Your Own Model Rockets
Now that you have all of the necessary materials to build your own rocket You can begin.
- Take your class 125 pvc pipe (either the 1/2" for the "C" engine rockets, or the 3/4" for the "D" engine rockets) and cut of anywhere from 6"-12" off of the pipe using either a hacksaw or a PVC pipe cutter. Note: making your rocket longer will increase stability but decrease maximum altitude attainable by rocket. longer rockets may also need larger fins.
- After your tube is cut to length use sandpaper to clean the ends of the cutoff pipe.
- Next you will have to make the fins for you rocket. I recommend using thin but strong cardboard like the type that most pizza boxes are made from. The fins can be cut out in any shape that you want, but they should be of ample size to stabilize the rocket. I recommend that the fin be at least 1/3 the length of the rocket and 3 times as wide as the rocket tube. Simply draw a fin on the cardboard and cut it out, then use that fin as a template for the other fins. It is a good idea if you are building many rockets to keep an extra fin as a template so that you can be more consistent with the fins. Rockets may have 3 or 4 fins.
- Now you are ready to glue your fins on to your rocket tube. I recommend using a hot glue gun to attach the fins to the tube because it solidifies in a matter of minutes. (Caution: Hot glue can burn always follow manufacturers directions when using a hot glue gun.). If a hot glue gun is unavailable you may use any glue but extra care must be taken to allow the glue ample time to dry before launching. Glue the fins on radially around the rocket tube (i.e.: if you are using 3 fins they should be 120 degrees from each other and perpendicular to the tube.).
- Now you are ready to insert the engine into the rocket. Insert the engine into the bottom of the rocket (The side closest to the fins). In the case of the class 125 PVC pipe the engine may be smaller than the inside of the pipe if this is the case use some masking or duct tape to wrap around the engine until the engine fits snugly into the pipe. To assure that the engine is not blown out of the rocket by the ejection charge you may want to glue it in place.
- Once the engine is in you can put a nose cone on. The nose cone can be made out of paper or it could simply be an end cap for the size pipe that you are using. The end cap can be glued on or not depending on the application that the rocket is being used for. If you do glue on the end cap use PVC to assure a strong seal. Note: For the purpose of launching rod clearance it may be necessary to cut out a piece of the end cap. See. Launching the Rocket
- Take a drinking straw and glue it on to the tube of the rocket. This will act as a guide for the rocket when it is launched. If you have cut out part of the end cap make sure to glue on the straw so that it lines up with the cutout.
- If you actually want to recover your rocket (I personally never really do since they are so cheap to make) You may use a plastic bag as a parachute. Cut out a circular piece of a plastic bag and tie strings through holes in the edge of the bag then make just as many holes in the top of the rocket. Fill in the rocket with some fire retardant paper or cotton and stuff the chute into it. Put the end cap on but don't glue it on. The ejection charge should blow out the chute and the rocket should come down slowly to earth. (Caution: The end cap will not come down slowly and may cause injury stay clear of the falling rocket and end cap.)
Your own homemade rocket
When starting to design a rocket, sit down and plan out your ideas. Think about these things:
Next, draw out your plans. The picture dosen't have to be perfect, just a brief sketch. From these plans, you can then go directly and build your rocket, or draw them to scale, labeling the measurements.
- What type of engine do I want to use?
- How long should the body tube be?
- Which recovery system is appropriate for the design I'm thinking about?
- How big do the fins need to be? What shape should they be?
- What parts am I going to need to build this?
A good recovery system means the difference between a rocket that is still in one piece after launch, and a mess of pieces that is just barely recognizable as a model rocket.
Six major kinds of recovery systems are used in rockets:
- Featherweight: This form of recovery relies on a very small rocket. Designed with a blunt nose, these rockets fall slowly to the ground after the engine has been ejected. Sometimes a streamer will be attached to the engine, but this is not necessary.
- Tumble: The ejection charge pushes the engine backwards until it is stopped by an oversized engine hook , making the rocket unstable. The model tumbles as it falls, creating drag to slow it down.
- Parachute: By far the most common, a parachute acts as an air brake, slowing the descent of the rocket by increasing drag. The size of a parachute will vary depending on the model. Parachutes that are too small will cause the rocket to come down too quickly, and this could damage a model. 'Chutes that are too large, however, may catch the wind and drift for a very long time before reaching the ground.
- Streamer: Streamers bring a rocket down slowly without the drift that may occur with a parachute. The longer the streamer, the slower the descent.
- Glider: One of the most interesting forms of recovery, glide rockets are launched like any other rocket, but upon reaching apogee, the model converts to a glider, using wings for lift, circling back to the ground. The booster may be attached to the glider, or it may detach and use one of the more conventional methods (ie: streamer) to fall back to Earth.
- Helicopter: Perhaps the strangest of all (and least common), this method uses vanes that make the rocket spin as it falls. These vanes are activated in various ways by the ejection charge of the engine. If you have designed a rocket like this, we would like to see it. Please send mail to firstname.lastname@example.org and tell us about it!
Designing With Stability In Mind
When designing a rocket, you must be sure that the rocket will be able to fly straight. This ability is called stability. There is one basic rule: keep the center of pressure ahead of the center of gravity. You must keep your fins large enough to do this.
Testing For Stability
With every model you design (and even those you build from kits), you must test their stability before launching them. This can be accomplished safely with a swing test.
If the rocket is stable, the rocket will 'fly' with the nose pointed directly into the line of flight (or 90º to the string).
- Start by finding the center of gravity. It is usually right on or near the launch lug.
- Second, tie a string around the body tube at the center of gravity so that the rocket balances perfectly.
- Third, swing the model around your head by the string. Be sure you are in an area free of other people and objects!
Using multiple stages on model rockets allows them to go much higher than a simple one stage rocket allows.
The first stage engine is ignited as always, electronically. These lower stage engines have no ejection delay, and are color coded with red labeling. As the rocket burns, the upper retaining cap ruptures, sending hot gas up into the next stage, igniting it, and throwing the lower stage tumbling back to earth.
The upper stage engines are usually designated in purple, and have a long delay time, allowing the rocket to continue coasting upward.
Each engine is taped to the next one using clear cellophane tape. This will burn away with each stage separation.
Since Multi-stage rockets tend to be tail-heavy from the added engines, the fins must be much larger than single stage rockets. Each stage must have progressively more fin area than the stage ahead of it, generally at least twice as much.
When testing Multi-stage rockets for stability, it is important to make sure that it will be stable throughout the entire flight. This can be done by testing it first without the booster stages, then adding them one at a time, and testing again.
Finishing the Rocket
Almost as important as stability and fin design is the way you finish your model rocket. A bad paint job can slow a rocket down, and keep it from reaching its maximum altitude.
In order to get the smoothest coat, it is best to first use sanding sealer on all the balsa surfaces.
Several thin coats are much better than one thick coat. Hold the spray can about eighteen inches from the model, and move the spray can back and forth along the rocket. Allow each coat to dry before applying the next.
Masking is used to create rockets with more than one coat of paint. If you want the fins to be blue, and the body tube red, you would do the following:
With practice, you will be able to paint intricate designs using masking.
- First: spray paint the entire rocket blue, and let it dry.
- Second: use masking tape to cover all the areas that are supposed to stay blue.
- Third: spray the model red, and then let dry.
- Fourth: slowly peel back the tape, revealing the blue fins underneath!