Intro: Design and Build a Rocket
I figured it was time for me to make an instructable. I have been on the site for some time and feel it’s time I contribute.
In this instructable I will show you how to make a quality model rocket for cheap from start to finish. No kit or commercial parts will be needed but you could use them if you wish.
• ruler / straight edge, you will need a long and short one
• cotton swabs (optional)
• razor saw (optional)
• hobby knife / razor
• plastic container / cup / bowl
• sandpaper, from 220 up, depends on how you want the final finish
• dremel (optional)
• drill (optional)
• clamps (optional)
• glue, white glue and wood, if you only use one use white glue
• balsa, block and sheet
• masking tape
• craft paper
• glazing putty, automotive (optional)
• spray paint
• tubes to form/make the body tubes, could be a pvc pipe or a shipping tube, just as long as it isn’t too big, you can also use tubes from paper towel rolls and rolls of plastic wrap and aluminum foil make good tubes
• motors, whatever size you want
• launch rod
• recovery wadding
• elastic cord, for shock cord
• chute material. ripstop nylon, heavy trash bag, maybe a chute ible in the future
• something to use as clamping plates (optional)
Sites and Software
• open rocket, free model rocket design and simulation software
Rock Sim, offered by Apogee, more powerful and from what I have heard you are able to model more complex rockets but the cost is about $120usd
• http://www.rocketryforum.com/, lots helpful people and info
• Nar.org, good info for people getting started
• discountrocketry.com, lots of parts and good prices if you plan on using commercially available parts
Step 1: Making Tubes
For this step you will need the craft paper, cup/container, white glue, sponge and whatever you are going to use as a tube form. Of course if you are going to use a found tube you can skip this.
You will need to do a little planning at this point. You need to know how big of a rocket you want to build and what motor/motors you want to use. Once you have figured out what you want to use as a form you need you need to figure out how many tubes you need to get the desired length.
Pvc pipes and mailing tubes make good forms but anything that is straight, round and sturdy will work.
Lay your form to the side and get ready to cut some strips of the craft paper. I usually cut mine about two inches wide because that is how wide my large ruler is and I make them as long as the ruler. Test fit a strip to see if it will make it to the end and it fits the way you want, if it’s short make the next one wider. Go ahead and cut a few as you will need several layers to build the tube.
Take your first strip secure it with tape to one end and wrap it around your form spiraling up like a candy cane. Make sure there are no gaps and secure the strip at the other end with another piece of tape. No glue is put on this first layer.
Now you need to mix the glue in a container. Mix glue and water till the mix is about the consistency of buttermilk, maybe a bit thicker.
Using the brush/sponge we can wet out the next strip to go on. You don’t want to completely soak it because the paper would probably just fall apart, just enough to coat the paper. You will need to work quickly on this step. This strip will be offset from the first, use the seam from the first strip as a guide. If you put it on nice and straight it will stay flat and keep an even seam all the up. Repeat this two more times to make a total of four layers.
At this point you will need to set it aside and let the glue dry. After the glue has dried you can add another few layers or if it turned out good leave it as it is.
Once you are happy with the tube you will need to remove it from the form and trim the ends. Take a piece of masking tape and wrap it around the tube so it lines up with itself, this will give you a straight line to follow. Make sure you are cutting down far enough that you will cut off all of the loose and uneven ends. Using the cutting tool of your choice remove the excess. You can use a dremel and a cutoff wheel for this too. Do this for both ends to get a good tube. If you want a rocket longer than the tube you have I will show you how to connect tubes later.
Tubes for motor mounts. Take at least two motors and tape them together end to end. Cut a strip of craft paper that is wide enough to go from end to end of the motor stack. Wrap the paper once and make sure to keep it tight and straight. I had a piece that was 710mm long and when wrapped was about 1.5mm thick tube which is a bit on the thick side, half that would probably be fine. Make sure you make the tube long enough to accept the longest motor with that diameter if you think you might want to go bigger. You will want the finished mount to be a little shorter so you can grab the motor and pull it out. You can sort motors by dia in open rock and see what the longest motor would be. Be sure to remember room on the end for the motor block to come in later steps.
You will also need a motor block, I usually use a piece of used motor casing of the same size. If you need to make one wrap craft paper around something smaller that would give you a thickness of around 3 to 6mm and fit in the motor mount tube. You will cut a length of this off to use as a motor block.
Do the same with the launch rod but only a few wraps, this will be used to make the launch lugs that will hold the rocket to the rod as it leaves the pad.
Step 2: Open Rocket
Now that we know what size the bt is and we know what motor we are going to use we can really figure out how we want to build the rocket.
After downloading open rocket all you have to do is open it. The program is a .jar file and runs from the file itself, so plop it down on your desktop and away you go. The interface is pretty simple and includes sample files.
Looking at the simple rocket we see a blue outline of the main rocket components. Starting at the front we see the nose cone then, the body tube or bt with launch lug attached and at the end are the fins. On the inside we the shock cord, parachute, wadding and the motor mount assembly. We also see two dots, a blue and white one and a red one. The blue and white dot is the center of gravity (cg), the point at which the weight would be equal to either side. The red point is the center of pressure (cp). This is the point where the aerodynamic forces affect the rocket. The cp will always be aft of the cg.
As a rocket moves forward and is pushed by a gust of wind or jostled by a bit of turbulence it will want to rotate around its cg. By adding fins to a rocket we move the cp behind the cg and the cp will hold the rocket straight. Think of it as like this, if you could attach one string centered in the tube at the cg and it being pulled forward that would be the thrust and inertia of the rocket moving forward. Now imagine a string centered and attached at cp and being pulled to the aft that would be the aerodynamic forces working to correct the flight of the rocket. If the two points are spaced correctly the rocket will fly straight.
A number of things will move the cg and cp of the rocket, let’s look at cg first.
The further forward the cg is the easier it will be to make it stable. The length of the rocket has a great affect on the cg. The longer it is the further the nose cone will be from the fins. Think of the bt like a lever, the further out the weight is the more influence it has. Of course the heavier nc (nose cone) and recovery items are the more influence they will have but be careful of making them too heavy as the extra weight will affect the performance of the rocket. And the fins and motor and mounting assembly will want to move the cg to the back so be careful of long over hangs.
The cp is pretty much controlled by just the fins. The number, size, shape and location will affect the cp and stability of the rocket. The larger the fin and further back they are the more stability they can add to the rocket but everything is a tradeoff. The more and the larger the fins the more drag and weight they add. The larger and further back they are will move the cg further back. You can also make the rocket over stable, where the fins have too much control, if this happens a rocket could be easily pushed by a wind gust a could go horizontal and that would be bad.
Step 3: New Model
With a finished bt you need to measure the thickness of the wall, take a few measurements and use the average, you also need the outer diameter and length. Even if you want to make a longer rocket put the actual length of the tube.
Click the body tube button in the top right window, in the new pop up enter your measurements. Don’t worry about the inner dia the program will correct it after you enter od and thickness. In this window you can also select the material as well as the finish of the surface. You have other tabs but they are not needed now. If you close the window and click the bt button again another window will open and a new bt will be created this time it will be the same as the other.
If you do not want another bt just delete it. If you do need another bt we will need to connect them. We do this by adding a coupler. With the top bt selected in the left selection pane click the coupler button. A new coupler will be created at the bottom of the bt. When making a coupler you can use just about any decent piece of cardboard, I usually use paper towel tubes. Measure the thickness of the tube and how long you want to make them. Move the coupler so that it half in the upper tube and half in the lower tube.
Now click the nose cone button. Umm, what, the nose can’t go on the back. It’s ok, just close the nc properties window and click the “move up” button until it’s where it should be. By double clicking the either nc itself or nc in the list on the left. Now we can set our properties. Under material scroll up and select balsa and click the filled button to the left. After selecting the nc shape you want, I would recommend an ellipsoid to start with. Next go to the shoulder tab. Set the size of the shoulder, the diameter should be the same as the id of the bt. When setting the thickness of the shoulder set to half the diameter since it is a solid piece.
Time for the motor
Select the lowest bt and click the “inner tube” button, go to the motor tab and click the “this component is a motor mount” check box. Now select the longest motor you plan to use. I’m going to use an e9-8.
Go here for an explanation of the markings for the motors go here http://en.wikipedia.org/wiki/Model_rocket
The motor will show on the model in solid grey, the motor mount tube will be purple. Adjust the measurements to match the tube you made. The motor I selected is 95mm long, I set the mount tube to 90mm long. With the motor tube selected click the “engine block” button, in the properties window set position to top of parent and zero the measurement. Adjust the measurements of the block to match yours. Now to secure the motor mount. Select the lower bt again and now click the “centering ring” button. The easiest way to make these will be to glue the templates that we will print from the program ta sheet of balsa so set the thickness to that. Make two of these. Set the rings a few mm from the top and bottom. You should now have a motor mount that will accept the longest motor you would plan on using and have enough sticking out of the end to be able to grab and pull out. You can make an adapter ring from a used motor by cutting it to the needed length. If you need to strap a motor down somewhere and safe and in a way that it will not come loose and light it off, clean out the residue and have a tube for motor block and spacers.
Select top bt and click parachute. For now we will adjust the position to below the nc shoulder and leave the rest as is. We eill test the rocket first and see if this chute is enough for the rocket. After testing if the ground hit velocity is say more than around 10mph you should adjust the size of the chute.
4, Finally the fins
Select the lower bt and click one of the fin buttons. I use the free form fin tool and make my own. Set the number of fins you think you want for now and set the material and thickness. Since I have such a short rocket my fins needed to be rather large. I usually try to get my stability between 1-2cal. I could have used four or maybe five fins and made smaller ones that could have worked as well.
On larger fins and rockets I would suggest adding fin roots/tabs that go to the motor mount tube.
The longer a rocket is the smaller the fins will need to be because the further forward the cg will be. The size and shape of the fins and if they lean or sweep forward or aft and how tall they are all have an affect on the stability. So if you use free form fins experiment with different shapes and angles.
5, little bits
Add launch lugs, preferable two. One somewhere high and one at the bottom using the measurements from the lugs you made.
Add the recovery wadding if you wish, it adds so little weight I normally don’t bother with it. You can also set the finish of the rocket surface and set the shape of the fins which both will effect the performance of the rocket.
Step 5: Testing
6, now we test
At the very top click the simulation tab and pick new simulation. Enter your launch site info as close as you can. Adjust launch rod length and run simulation. You will now see a bar with some info. I see mine has a warning. My chute opens at too high of a speed, almost 60. If you double click the results another window will open, click the plot flight. You will get a graph that will display some info. Looking at my graph I can see that there is too long of a delay after apogee so I can select a motor with a shorter delay. I select the e-9 with a 4 second delay and all is good chute opens at a happy 5mph. One thing to look at here is the ground hit velocity, mine is at 11.7mph. I usually go for around 10, if it is much faster make the chute diameter larger.
If you wish to really spend time on finishing the rocket and you give your fins a nice airfoil shape and polish all the paint it can really make a difference.
Step 6: Build
Now we print out our templates, go to file->Print/Export or ctrl+p. Make sure all are selected and click print. The print out will give you the specs of your rocket, the simulated performance with whatever motors you selected, a parts list, fin alignment guide and fin, centering ring and nc templates.
Take the template page and roughly cut out the pieces and glue them to a sheet of balsa. If you have narrow centering rings you may want to use cardboard as the balsa will be easy to break if it’s thin. If you need to make a sheet of cardboard glue pieces of the craft paper together and clamp between two flat surfaces. If you are patient and work carefully you can do thin pieces with the balsa, the paper template glued to it will make it a little stronger.
Take your time, you want these to be as accurate as possible, if they are off and they hold the motor cocked the rocket will never fly right.
If you have a dremel and the drill press stand you can use a cutting bit to cut out the rings.
Step 7: Fins
Cut out the first fin the stack however many more pieces of balsa you need to make the rest of your fins. Holding the fins together tightly and lined up sand the edges to make them smooth and even. Laminating the fins is optional but I recommend it as it makes the fins stronger and could help with fin flex in flight. After sanding use a fin as a guide to cut out enough pieces of craft paper to cover both sides of all fins. Spread glue over one side of the fin and smooth the paper out over it. I used two pieces of particle board from an old piece of furniture but anything big enough and flat will work. Stack the fins with something the glue will not stick to separating the pieces, clamp and set aside.
Once the glue is dry remove and use a xacto or sand paper to remove any excess paper. As an optional step you can bevel the edges to make them a bit more aerodynamic and have less drag and improve the performance of the rocket.
The further in on the face you go to sand the longer and sharper the edge will be and it will have less drag but it will be more delicate.
Step 8: Motor Mount
While the fins are drying you can assemble the motor mount. Glue the motor block in first, Then the centering rings at the locations you set them at in your model. Be careful as the measurements for the centering rings are measured from the bt and not the motor mount so you will have to figure out the measurements to mount them to the motor tube. Set aside and allow to dry.
Use wood glue to assemble the motor mount and white glue to glue it in the bt. The white glue will give you longer working time so you can slide it in to where it needs to be.
If you notice I do not use motor clips. I friction fit my motors in the tube, just wrap a piece of masking tape around the motor until it has a nice snug fit.
Step 9: Fins and Launch Lug
Cut out the fin alignment guide, tape it around the bt making sure it lines up with itself . Hold the bt up to a door frame and line up a fin line and use the door frame to continue the line all the way down, do this for all fin lines. Now you can take the fin guide off. apply a bead of wood glue the root and carefully line up the fin with one of the lines. If you designed your rocket with the fins shifted forward or aft make sure you make a way to position them correctly. Use something square lined up to center of the bt to make sure the fins are not leaning. After the fins are mounted add the launch lugs.
If your rocket is tall enough and you have enough space between the motor tube and bt you could notch the centering rings and put launch lugs inside. This could maybe improve performance a bit but it would also give a cleaner look to the rocket.
Step 10: Nose Cone
Sorry I do not have any pictures of me actually making a nose cone but here's the process.
Once you know how long the nc is you can cut your balsa block to length. find the center by connecting the corners and drill a hole that is just big enough for your wooden dowel rod. You will want a few inches extra of the rod to extend from the block, make sure the hole is straight. If you have access to a drill press I would use it. Squirt some glue in the hole and push the rod in, I would let it set and dry for at least a day.
Now you need to find or setup a lathe so you can turn your nc, I'm not going to cover that in this ible but there are plenty on here that show you how to set one up.
take the template for the nc and glue it to a piece of cardboard or balsa to make it stiff and cut out the nc shape and use it as guide for the shape.
Step 11: Recovery
Now we can prep the recovery items, take your chute (I’m not going over chute making in this one, maybe later), shock cord and a piece of paper. I mount my chutes a little different from how most people do it. Instead of attaching the chute to the nc I add an extension line and attach it to the bt opposite of the shock cord. I do this so that if the shock cord fails and the nc detaches the chute will still be attached to the rocket.
Step 12: Attaching Bts
To attach bts all you need is a paper towel roll or scrap bt. Cut it to the length you made it in open rocket and make a cut down one side. slide it in a open end of the bt and mark where it overlaps. Remove it and and cut on the line. Put some glue on the inside of the bt insert the coupler, twist it around and hole it straight and flat to the sides of the bt. Allow the glue to dry and glue the other bt to the coupler.
Step 13: Finishing
After all the parts are assembled you can begin painting it. I recommend sanding the whole thing with 220 grit and spraying it with primer. Spray two light coats and sand with 320 or 400and prime again. When you have a nice smooth finish spray the color on. In the pictures are a few of my rocket projects. All of my rockets have been scratch built, And I spend less than I would on a kit and I get to make it the way I want. I will buy kits from time to time if I can find them on clearance. Soon I will start making my own rocket fuel as well. That way I can make everything just the way I want it. Hope you enjoyed and happy building.
The zip contains rockets I have created in open rocket.
Hopefully soon I will do ibles for the launch controller, nose cones and others.
UPDATE: pictures of the finished rockets I was working on.