3d Printable Finless Supersonic Rocket

This single-print, glossy model rocket is a stepping stone into high-power model rocketry. It's simple to print, assemble, and reaches the sound barrier in under four seconds. It's not designed to go for height, just sheer speed, so launchers can relax when considering FAA limitations or losing their rocket miles from the original site.

The basis of this rocket emerged from nature itself; the general shape is largely based on a falcon's dive and a raindrop in free fall. It demonstrates the beauty of simplicity, proving improvement not by adding but by taking away. But without traditional fins, how does it remain centered? Why doesn't it erupt into chaos and scream in all directions??

The truth is, is does have fins. Well, sort of.

Rather than impose huge amounts of drag by sticking outside the rocket's base, the fins are inside the body of the rocket and invisible from ordinary view. The fins are what give the body it's rigidity whilst they hold the motor-housing and the aerodynamic shell together. But the fins still keep the rocket stable while it's making a sonic boom, they just act in a different way. Rather than keep the base stable with large amounts of air flowing over the fin surfaces, the supports are angled precisely at 67.5° and spin the rocket gyroscopically. Thanks to the concept of angular momentum, the body naturally wants to maintain it's orientation (in this case, upright) instead of veering off. In simpler terms, forces act on the rocket when it rotates so it's steady in flight. As a result, it can remain balanced without unnecessary drag, and it's visually striking looks make it a one-of-a-kind aerial display piece.

Before continuing, it's crucial to note that serious implications can occur from irresponsible use and failure to use proper safety precautions/etiquette. If you plan on making this, please first inform yourself on the dangers of hobby rocket motors and do not attempt to make your own. Caution is definitely advised, but with proper consideration and setup it can be a safe and entertaining project.

So, without further ado, let's blast into it!!

When determining what material to use for the rocket, there's two choices that are overwhelmingly superior to the others, but differ vastly from each other.

PLA Filament

1. Lighter
2. Cheaper
3. Easier to print + work with

https://us.store.bambulab.com/products/pla-basic-filament

Carbon Nylon-6 Filament

1. Slightly heavier
2. Expensive
3. Difficult to print + work with
4. Much better heat resistance
5. Stronger

https://us.store.bambulab.com/products/pa6-cf?srsltid=AfmBOoq3YH2DOxI8u6FJznczrYW9lYL5txjUUBsDjYGRgAF4uQsi-LnT

At a glance, it might seem easy to go with PLA, but considering what is personally best is up to you. It's important to note that carbon's added weight is very minimal, and it more than makes up for it in strength. If repeated launches (5 or more) is in the future, the intense conditions will make the carbon last much longer than PLA. Air/sound wave resistance and shooting flames also generate excessive heat that deteriorates the integrity of the rocket, so carbon again is much more resilient.

Unfortunately, it's over 3x the cost. Furthermore, without a custom printer nozzle and drying setup, it's nearly impossible to print. That's overlooking the fact that all your settings will need to be fine-tuned too, as standard tempreatures and flow speeds don't apply to the CN-6 filament. And, above all, it's been known to have dangerous side effects with improper handling due to microscopic carbon splinters entering the skin and causing irritation. If you go with the carbon nylon, please ensure it's sprayed with a standard clearcoat before handling without gloves.

At a glance:

For well-experienced printers with a larger budget - Carbon offers many benefits over PLA and is the way to go.

For typical printers with smaller costs - PLA is cheaper, lighter and easier to use, it just won't last as long.

Other Necessities:

Launch Grade Parachute/Streamer

10-inch Elastic Cord

Additional Options:

For Carbon Nylon-6 Filament - Standard Clear-Coat spray covering

Decals -Vinyl Sheets & Vinyl Cutter (Cricut)

Colored Spray Paint

Attatched below is the final rocket design for 24mm motors, ready for the slicer!

The first step is to determine what motor to use to reach the desired outcome, and before we can even begin to get numbers like drag coefficents and overall widths, we need to get a rough idea of what's possible. Manufacturers design motors for different purposes, and some simply won't ever hit the target speed of 343 meters per second, no matter what we end up with. Additionally, to keep launches somewhat achievable, something wildly excessive isn't needed. They will surpass the goal, but it's tough to get the thrill of launches again and again if the motor costs are high and rocket retreival isn't possible.

I use an online calculator and tweak the motor used along with the rocket dimensions (that fit in my printer, of course,) to get a broad idea of where to begin when designing.

https://www.translatorscafe.com/unit-converter/en-US/calculator/rocket-max-altitude/?mobile=1#about-rod-length

Eventually, after tedious trial & error, I decided on using an AeroTech G78. It's relatively affordable for it's results, plus it accomplishes a high speed in a short burn period so it won't soar too high. I settled on a maximum width of 50mm on my rocket, and combined with the nosecone it's approximately 380mm tall. It's not the largest rocket ever, but it's able to be 3D printed by most machines in only two pieces - the fuselage (main body) and the nosecone.

Here's a link to purchase the AeroTech G78, although I'll be designing a version for lesser 24mm motors as well.

https://www.apogeerockets.com/Rocket_Motors/AeroTech_Motors/29mm_Motors_Loadable/Aerotech_29mm_Loadable_Motor_G78G-7

Important Note:

When purchasing a motor, please make sure the delay charge is at least 7 seconds or greater. This prevents the parachute/streamer from ejecting prematurely, which at high speeds can cause damage to the rocket and even cause the release to fail, resulting in a potentially hazardous crash.

Using a CAD software, I designed the center structure of my rocket. This must be structurally rigid as it's the "core" of the rocket, and the hollow structure of the internal tube provides a chamber to store flash paper and carry the launch charge from the motor to the parachute. It's also vibration resistant, which at this scale won't likely be an issue, but it still helps maintain efficiency to keep the condition of the rocket largely positive. The motor unsuprisingly gets very hot, and obviously 3D printers work by melting plastic, so it makes sense that a thin layer around the motor is a poor idea. This should be the most dense part of the design to prevent decay as a result of heat, but luckily motor casings insulate thermal radiation fairly well so it'll still work.

When designing a model rocket like this one, it's important to stay safe with proper safety precautions and planning. Even still, prototyping takes a lot of time, resources, and effort to produce multiple failed iterations, so I like to prove concepts digitally. There's a few good ways to go about this, but I use a free software known as OpenRocket. Sure, there's a mild learning curve, but it's free, accurate, and a great way to test ideas before building them in the real world.

With that being said and 6 concepts tried in a virtual atmosphere, the rocket needs just over 11,000 rotations per minute (rpm) to be stable at low mach-speeds. It's impossible fully comprehend how destructive centrifugal force can be on this scale. While the rocket obviously needs to be stable, the same feature that enables this also has the power to tear it to shreds. Thus, adjusting the needed angle to provide for more rotation dosen't need to be excessive, and grossly overesimating can be fatal to the rocket.

With some simple math using the estimated speed, various angles and forces of drag, I calculated the angle of the fins to be 67.5 degrees to the horizontal plane. For optimal efficiency, the higher fins will be slightly shorter in length than the lower ones, which will help streamline the twisted air.

There's a solid internal structure now and the support rods will effectively spin the rocket in flight, and we have a housing to match our exact power unit, but if it was launched now there'd be a lot missing. More specifically, it's missing the sleek body that minimizes drag in flight.

Every design begins with an idea, but I like to figure out the top and the bottom before working into the middle sector.

At the base, there's large supports and a motor housing, but it needs to be tapering in order to establish clean airflow. It's similar to the tail of a raindrop: the gradual blend back to minimal turbulence produces less vacuum forces that drag the ship backwards. This'll also help force the air over the bottom supports as it squeezes it through a compressing tube, forcing more air over the angled spots and heightening the spin. If that's still confusing, it's similar to a ramjet engine in a lot of ways. The bottom two inches will be more or less an upside down cone with a hole in the bottom to let air pass. To collect more air, it will also be 1.5mm wider than the next-widest part of the body, allowing it to "scoop" air right into the vent.

There's a lot of nosecones to choose from, and all serve different purposes. For example, the design for subsonic, transonic, supersonic, and hypersonic cones all vary due to how they interact with air resistance and the buildup of sound waves. In less dense air, it's actually easier to achieve supersonic speed since there's less resistance on the rocket, but the nosecone still directs air over the rest of the body and reacts to the environment.

More blunt, rounded rocket tips actually work better at subsonic and hypersonic speeds. At these speeds, sound waves aren't as big of an issue as they're either travelling much to quickly or too slowly, so it makes sense to use a less-pointed tip.

Approaching the sound barrier, however, a conical spike is more suitable for dealing with the buildup of waves. While a blunt tip establishes a wall of waves that slow the rocket, a conical tip largely helps peirce through them to keep the rocket moving. As the ambition is 750mph+, this is the suitable choice.

Now that we know what type of nosecone we want, how do we determine it's size? Naturally a longer nose is more efficient, but also less stable as it moves the center of gravity farther away from the base.

Generally, a good rule of thumb is the nose needs to be between 8% & 16% the length of the rocket's body. Since we already know the rocket's body is 14 inches long, the nosecone needs to be streamlined and roughly 1.70 inches in length. However, that's excluding the length needed to fit snugly into the rocket body, so we'll add a skinnier, inner tube 0.50 inches deep that will tolerantly fit into the payload/parachute bay.

Okay, so we have a pointy nosecone and a sleek tail, with spin inducing support ready for liftoff. Now all that's missing is the primary section of the body!

There needs to be a way to seamlessly fuse the nose shape and the tail, so a cylinder seems like a logical choice. It's simple, symmetrical, and very common on other model rockets. But this isn't an ordinary rocket. There also needs to be a way to get air inside the rocket to make the whole thing spin, which requires a bit of background knowledge on the function of vacuums and how they form.

Household vacuums suck air and debris into a chamber by creating a low-pressure zone. Gas molecules are constantly bumping off of each other, so when an area has less gas molecules to hit, they fill up that area. But, if it's never filled (gas molecules are constantly removed), then the suction loops and creates a vacuum! I tried to make a vacuum chamber on the side of my rocket, but first there needed to be some hole to draw the air inside. Not to brag, but they're as stylish as they are effective, and the teardrop shape that helped inspire the rocket is the silhouette for the four holes.

As air rushes over the nose, it wants to keep moving over in a straight line, but an increased bulge in the nose pushes it outwards, eventually establishing less airflow over the valley on the side of the rocket. This is the low pressure system, and (can you see where this is going?) a vacuum of air pulls it through the side vents, into the rocket, and over the spin-inducing supports! To keep the air from falling backwards over the new vacuum, we'll also widen the lower half of the rocket slightly while also feeding a slight taper into the powerful rear blades. This also creates yet another internal compression zone, maintaining the spin even more effectively.

There's A LOT of aerodynamics into this, and the laws of gaseous fluids are a bit blurry and highly complex. So many more contributions and countless wind tunnel tests went into designing the bodywork, but for the sake of keeping this a little easy to understand and concise, I'll cut anything a bit excessive out. I highly encourage anyone interested to learn more, as there's so much to learn and so many applications to use.

It's time to get this onto the 3D printer. It's designed to be light, so it only goes through 100g of PLA, but make sure your printer can handle the build size.

My Longer LK5 Pro isn't great at much, but it does have a large build volume that allows it to do projects of this scale. If you have an at-home printer that can't handle it, try reaching out to your library, or if you're a student, check your school/university. Places like these often have funding that allows for a greater variety of printers, but if that still doesn't work select companies offer printing services digitally.

In order to perserve the rocket and avoid legal/saftey trouble, the rocket needs a way to slow down. This can be done in one of two ways, either with the use of a parachute or a streamer. Depending on where you launch it, you might prefer either option, but both have special features that make it attractive. The cost is relatively the same for both, which is fairly inexpensive at this scale ( > $10.00).

Parachute:

1. Slow the rocket down more, much slower descent
2. More reliable if packed properly, if not then strings are known to tangle.
3. Often blow further away from the original site due to wind
4. Prone to getting stuck in trees

Good to know -

Ensure it is packed properly! Attached is a link to the MIT Rocketry Team that covers the simple yet vital process in detail:

https://wikis.mit.edu/confluence/display/RocketTeam/How+to+Pack+a+Parachute

For a streamer, simply roll it up so it fits inside the rocket tube.

Streamer:

1. Slow the rocket down less, more rapid descent
2. Slightly less reliable
3. Often remain closer than parachutes to the original site for easier retrieval
4. Less prone to getting stuck in trees
5. Highly visible, most are a long, brightly colored reflective strip

Good to know -

The optimal ratio of length:width to maximize the flapping drag that slows the rocket is 10:1. So, if the streamer's the advised 2-inches wide, it should be 20 inches long.

Attatch your streamer or parachute via an elastic cord to the rocket. MAKE SURE to tie the cord to the rocket body, nosecone, and recovery device!! It's better to be safe than sorry, often it's best to double knot the connections and apply a dab of superglue on the knots.

1. Choose a Safe Launch Site & Conditions

1. Clear & Open: Launch in a large, grassy field away from dry grass, trees, buildings, and power lines.
2. Low Wind: Don't launch in high winds (over 20 mph) or threatening weather, as it makes recovery unpredictable.

2. Maintain Safe Distance & Countdown

1. Establish a Zone: Keep spectators at a safe distance (e.g., 15 feet for small motors, 30+ feet for larger ones).
2. Use a Countdown: Always use a clear countdown to alert everyone before launch.

3. Use Proper Equipment & Procedures

1. Certified Motors: Only use commercially made, certified rocket motors and never tamper with them.
2. Safety Key: Always remove the safety key from the launch controller until ready to launch.
3. Protective Eyewear: Everyone at the pad should wear eye protection.

4. Prepare Your Rocket Correctly

1. Fireproof Wadding: Use flame-resistant recovery wadding to protect the parachute or streamer.
2. Vertical Launch: Launch from a rod or rail pointed as close to vertical as possible (within 30 degrees).

5. Be Prepared & Smart About Recovery

1. No Dangerous Recovery: Never try to retrieve a rocket from power lines, tall trees, or other hazardous locations.
2. No Catching: Do not attempt to catch a descending rocket.

Have a great time building amateur rockets, learning about aerodynamics, 3D printing, and most importantly, make it spin!