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Mar 17, 2021
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How to Build a Rocket

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I’ve wanted to get into high-powered rocketry for a while now, so this year, I decided to jump right in to the hobby and start learning how to build, fly, and recover large rockets.

For this project, I built a 6′ tall rocket capable of flying motors that can be used to get Level 1 and Level 2 certification through Tripoli. With one of the larger motors, this rocket will be capable of flying over a mile in altitude and hitting mach 1 on the way up.

Before you start, do some light research on high-powered rocketry to get a feel for what kinds of things you can do with the hobby. Also, it would be a good idea to join Tripoli or NAR as they are the national organizations (in the US) that handle certification.

If you are just starting with the hobby, I recommend building a kit for your first rocket. Depending on what your plans are, there are a wide variety of kits to choose from. I ended up buying a HyperLOC 835 kit since I would be able to earn both Level 1 and Level 2 certifications without having to do any major modifications to the rocket between flights.

For the motors, Cesaroni reloadable kits are perfect for starting out with. You can get motor cases in a variety of sizes, and for flights, you just buy propellant refills and reload the motor case each time. Make sure, though, that you match the motor diameter with the diameter of the motor mount with your kit.

Supplies:

  • Rocket kit
  • Epoxy (JB Weld is one of the best for general rocketry use)
  • CA glue
  • Spraypaint
  • Eyebolts
  • Kevlar cord (I think the cord I use has a 900lb rating)
  • Fire blankets (for protecting your parachutes)
  • Altimeter (I used redundant Missileworks RRC3 altimeters for electronic parachute deployment)
  • Tracker (I used a basic morse code ham radio beacon to track with a directional antenna on the ground)
  • 2-56 nylon machine screws (used as shear pins to keep the rocket together during flight)
  • Electronic matches (used with the altimeters to set off separation charges)
  • Black powder (FFFG for separation charges)

Tools:

  • Drill
  • Sander
  • Saw
  • Soldering Iron

Crash Course in Rocket Motors and Rocket Science

  • One of the most critical aspects of designing a rocket is making sure the center of mass is in front of the center of pressure throughout the flight. If not, your rocket will spiral out of control and crash. If your rocket is already built, adding a heavier nosecone or going with a smaller motor can help with this.
  • Motors have different letter classes based on their total impulse, with I being the lower end of the high-powered spectrum
  • Motor diameter typically falls into standard sizes. 38mm and 54mm are super common for general high-powered rocketry, but you can get even larger 75mm or 98mm motors at the upper end of the high-powered spectrum.
  • Solid propellant comes in “grains”. Grains are basically just propellant segments that get loaded into a motor casings
  • Motors typically come with a delay fuse and separation charge. While this is good for most flights, you will be relying on the fuse to burn out about the time of apogee. Too early, and you risk deploying the parachute while the rocket is moving too fast, zippering your rocket body, and too late, the force of drag from decent on the nosecone might not let the segments separate. Using an altimeter to set of your own separation charges takes a lot of the guesswork out of this process.
  • The thrust curve of a motor is important to look at for seeing when the motor hits max thrust and how long it will provide different levels of thrust
  • Motor burnout can cause early rocket separation if your sections are not coupled tightly enough together. Shear pins help prevent this.
  • When in doubt, google is your friend, but consulting an expert or seasoned veteran of the hobby can be incredibly valuable.
How-to-Build-a-Rocket-Article-Bookshelf

Start with attaching the motor mount centering rings and fins to the motor mount tube. If your kit has through-body fin mounts like mine, a super helpful tip is to extend the fin slots all the way to the end of the rocket so you can add and remove the motor mount assembly and fins as you are working on securing everything. Add the eyebolt for attaching your parachute harness along with some extra epoxy to keep it in place. Before gluing down the centering rings and fins, dry fit everything together a couple of times to verify it all fits properly. Also, DO NOT attach the rear centering ring until the assembly is mounted to the body tube. This will allow you to access some of the internal portion of the body while you are gluing it up.

When you start gluing things together, start by tacking all the pieced together with CA glue, making sure not to get it on parts you don’t want to glue down. This will dry fairly quickly and give you a strong enough joint to add the epoxy fillet to really hold everything together.

Some additional build notes:

  • When in doubt, too much epoxy is better than not enough
  • While not always necessary, you can reinforce your fins by “papering” them. This just consists of spreading wood glue or white glue over a sheet of computer paper or cardstock and then applying it as a skin to the face of the fin. Once it dries, you can paint over it like the rest of the rocket body
  • LABEL EVERYTHING. Nothing fits back together perfectly if you drill holes or make cuts on the body tube, so label how everything fits back together. There’s nothing worse than prepping your rocket and realizing none of your holes line up properly. To start, just mark the joints with a pencil, but you can keep your markings on the inside of the rocket to give it a cleaner final look. Also, one option is to paint the rocket a solid color and add a single stripe down the length of the body.

The avionics bay is somewhat straightforward to assemble. Figure out what all you want to fly, position them on the avionics bay sled, and add some walls and harnesses to keep everything in!

Usually, the most challenging part of this step is getting everything to fit just right. If you got a HyperLOC 835 kit, the avionic bay is big enough to fit a GoPro, tracking beacon, two RRC3 altimeters, and all the batteries needed to power everything. You may also need to solder up some wire harnesses for the altimeters and batteries if you do not already have some.

On the outer walls of the payload bay, I mounted pairs of small steel tube sections to hold the separation charges. Terminal blocks with bolts that go through the walls give the altimeters electrical access to the separation charges when the payload is fully assembled.

One important thing to note is that when adding switches for your altimeters, make sure they are accessible from the outside of your assembled rocket. You should not arm the altimeters until you are at the launch pad, and it is not reasonable to assemble the rocket on the pad. An easy (and low-profile) way to achieve this is with key switches mounted on the rocket’s body.

Give it a cool paint job since that will make the rocket fly better… JK, give it a cool paint job since you’ll want it to look nice when you show off your new creation to your friends and family.

Painting the nosecone (if it is polypropelene), is difficult if you don’t take your time, but roughing the surface with some sandpaper and adding a plastic primer first will make it an easy task.

After your rocket is assembled and painted and your avionics bay is done, the last two things to do before flight are making your parachute harnesses and testing separation charges with the shear pins.

There’s no set measurement for a good harness, but one rule of thumb is to mount your parachute so there is a 4:1 ratio of harness on either end of the parachute. For this setup with the separation charges mounted to the avionics bay, I had the shorter section of harness for both the drogue and main chute mounted to the avionics bay. I went with ~15′ sections of kevlar cord for both harnesses.

When you are measuring the cord, it helps to lay it all out to get a feel for how the rocket sections will hang on the way back down. It’s important to have everything offset so parts don’t bash into each other on the way down.

For separation charges, it is important for them to be powerful enough to separate the rocket sections and deploy the parachute but not powerful enough to blow up your rocket. It is possible to fly without shear pins, but adding shear pins gives you a known separation force. With 3 nylon 2-56 screws, this comes out to roughly 180lbs needed to shear the pins and separate the rocket. There are numerous online calculators that will tell you how much black powder is needed given the size of your body tube and the number of shear pins you have, but NEVER go with the simulated value. Start with a much smaller charge, and then keep testing larger and larger charges until you reach a charge size that is suitable.

Also, you will need to add a plug to the end of the motor retainer for testing the separation charge. This can just be a piece of wood the same shape and size as the bottom lip of the motor casing.

To test the pins and charge, you can use a vacuum taped to an avionics bay access hole to simulate the decrease in air pressure experienced during flight. My altimeter said it got all the way to 580 feet during the ground test!

One final thing for launch prep is to pack ahead of time. Make a packing list, check it a couple of times, and make sure you haven’t forgotten anything you will need for launch. My kitchen and entryway were a disaster the days leading up to launch

For flight day, make sure to bring all the tools you will need to assemble and fly your rocket. At the very least, have a screwdriver set, extra epoxy, some duct tape (and kapton tape if you’ve got it), the rocket motor, and igniters and black powder you need, a small scale to weigh the black powder, and of course, your rocket!

Remember to have fun and be safe and follow all rules and regulations while out launching! This flight was my first high-powered rocket build, and I was able to earn L1 certification from the flight.

No matter how much prep work and planning you do for a launch, things can still go wrong. After my successful Level 1 certification flight, I started planning for an L2 flight for the next launch. I spent my evenings leading up to the launch prepping the rocket, running simulations, and making sure everything was ready for a weekend trip out to launch. After I got out to the launch site and camped out overnight, word came in that the FAA never finished processing the altitude waiver, so nobody got to launch anything that weekend.

Fortunately, this wasn’t a catastrophic failure with my rocket, so it just amounts to waiting for another launch window, but the downside is that I likely won’t have an opportunity to launch for a couple of months. Still, I took the trip as an opportunity to work on my photography, tag up with my rocket friends, and do a bit of desert bird watching!

The takeaway is that if you want to get into high-powered rocketry, it is only a matter of time before you have a launch failure. When you do encounter a launch failure, make sure to analyze the failure as mush as possible since it is an invaluable opportunity for improving your rocket designs/builds and putting measures in place for preventing failures like that in the future.

Another launch opportunity finally opened up, so I went out for my L2 certification. I flew a Cesaroni K820 motor, which was about the biggest motor I could fit in the rocket without needing more parts or body upgrades. Overall, it was a super successful flight, travelling to ~9100ft and passing mach 1 on the way up. Landing was only 3/10 of a mile from the launch site, so the recovery hike wasn’t too bad.

This flight was also a great demonstration of the importance of having trackers on rockets going really high or really fast. It was almost impossible to see the drogue chute at apogee since it was almost two miles up, so everyone watching lost sight of the rocket on the way down. Without having a tracking beacon as part of the avionics payload, there’s a good chance we would have either had to hike a lot longer than necessary to find the rocket or lost it completely after landing.

There are so many different things to explore in high-powered rocketry, and sometimes the most difficult aspect of the hobby is limiting your focus enough to finish the builds. You can make solid propellant, experiment with hybrid engines, build scale models, break the sound barrier, fly complex avionics payloads, among a wide variety of things, so there is something for everyone in rocketry. My next flight should be able to hit mach 1, so I’m working on learning about supersonic flight and how rocket designs change for different speeds.

Future Plans

I will definitely be building and flying many more rockets to come. This rocket may only be able to fly up to 8000ft or so, but I hope to someday build a rocket big enough to launch a small cubesat payload into orbit.

The most important piece of advice I have for new rocket scientists, though, is to remember to have fun along the way and learn as much as possible!

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