3d printed fins idea

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Ccoen

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So a team and I are working on a rocket to go to 1 mile in the air and we currently are somewhat in a good stage but I am not sure what to make our fins out of. I am leaning towards 3d printing as I believe it would be the easiest and quickest option. Currently, I have been looking at materials and I am having issues determining what would or would not work. I don't think petg would be strong enough but I'm not sure, unless I find a carbon fiber reinforced option but I'm not sure if that would help. Then there's PA6-cf which has a stronger tensile strength than petg but I wasn't sure if there were other better options at a low price point. This is what I was looking at https://www.amazon.com/Polymaker-PA6-CF-Filament-Carbon-1-75mm/dp/B08T1ZQFKR.
So essentially my question is what has been used by the rocket community in the past when it comes to fins?
According to open rocket, our current design's max speed is 607ft/s and the max acceleration is 175ft/s^2 although that is the best-case scenario.
 
Why 3D printed over traditional methods?

Not being a smarty smart smart, but asking the question. (I'm mentoring a few teams, so I tend to ask the 'pointed' questions' :D )

3D printed fins do have some advantages, but they can be weaker than traditional wood / G10 / other composite lay-ups. You also have a [potential] weight gain. Aerodynamic fins look cool & sound cool, but rarely give the performance expectations..
 
Do you have a 3d printer that can handle the required temps? Are you experienced with 3d printing?
Are you printing the fins themselves? Or are you printing a fin can?

Lots of question. But DrWogz is right, they tend to be far heavier and beefier than traditional methods. Do some searches in the HPR and the 3d print sections here, there are several threads on this (including mine). I have been printing in PETG at this point, then fiberglassing the fins. Other than the novelty factor, don't see much benefit over standard TTW fiberglass or plywood fins.
 
Another option would be to print molds, so you can lay the glass or carbon down to get the shape you’re after, and it would be easily incorporated into the tube/motor mount structure.
 
The material listed is strong and easy to print. If you adjust the infill, you can maintain strength and print them light enough for rockets. Most new 3D printers can handle that temperature out of the box. They would only be heavier if you up the infill. Experiment till you get the weight you need.
 
If you are going to 3D print then design appropriately for the speed you get in your simulations. Don't forget you can make the fins thicker at the root and thinner at the tip to take the flight stresses appropriately. Remember twice as thick for a flat plate is actually eight times stiffer.
https://en.wikipedia.org/wiki/Second_moment_of_area#Rectangle_with_centroid_at_the_origin
Tapering also means the fin is less likely to resonate in the airflow.

I would also probably try to have fin shapes that didn't hang out the back, so to better survive the landing.

Remember that a 3D print is just another way of making something. If it is engineered to be fit for purpose it is a suitable material to use.
 
Why 3D printed over traditional methods?

Not being a smarty smart smart, but asking the question. (I'm mentoring a few teams, so I tend to ask the 'pointed' questions' :D )

3D printed fins do have some advantages, but they can be weaker than traditional wood / G10 / other composite lay-ups. You also have a [potential] weight gain. Aerodynamic fins look cool & sound cool, but rarely give the performance expectations..
There's not really a great answer to your question but its mainly just because I think it would be fun to do, It's in a program through my high school and the years past have all been more traditional methods except for one 3d printed fin set so I thought it would be interesting to give it a go.
 
Do you have a 3d printer that can handle the required temps? Are you experienced with 3d printing?
Are you printing the fins themselves? Or are you printing a fin can?

Lots of question. But DrWogz is right, they tend to be far heavier and beefier than traditional methods. Do some searches in the HPR and the 3d print sections here, there are several threads on this (including mine). I have been printing in PETG at this point, then fiberglassing the fins. Other than the novelty factor, don't see much benefit over standard TTW fiberglass or plywood fins.
We have a wide range of printers available that would be able to handle most materials that we would be using. I personally have a fair amount of experience 3d printing and I am getting better at the designing process. I was thinking of making the fins themselves with tabs on them that would go into a mount inside the body tube. Then we would glue them in and make sure they are tight on the body tube. I will look into fiberglassing them if we use a less resistant material, hadn't thought of that. It mainly is for the novelty factor as most of the teams in the program before us had done traditional fins.
 
then go one step further, and make a whole fin can. either make the a fin that interlocks with the others, or a whole unit. then that either lives inside / glued to the motor tube & the inside of the body tube, or some combination thereof..

Think also to a make a shell of sorts, and use some traditional materials as stiffeners / ribs, etc.. (like a dowel pin to give it some extra strength along its length..) Think of where you need strength & stiffness, and where you don't.. Design accordingly, especially with a 3D printed fin! Don't forget to take into account how the part will be printed, so that your layers are aligned with the least stress..
 
Do you have a design in mind? I am willing to print a set for you to try.
 
I’ve printed 3D fin cans that have flown on H motors just fine. I printed it as a single unit using an OpenSCAD fin designer that I think was done by VCP. PETG is plenty strong enough, although it takes a while to get the settings dialed in to keep stringing under control. The fins have a built in fillet which seems to add to their strength. I filled the surface of mine with Bondo spot glazing putty to create a smoother surface after I sanded them lightly. I would say that’s the biggest challenge, getting a nice smooth surface.


Tony
 
For my ABS nosecone I smothered it with CA glue then sanded. Repeat three time and I had a nice smooth NC.

When I started flying that seven years ago people looked at me like I had two heads. There is a high degree of resistance to change. It has had dozens of flight, up to M1.4 and shows no signs of wear.

This is the 4" NC on my Nike Apache and I also use it on the Velociraptor.
Mated1.pngPhotoComplete.jpg



The point is if a part is designed correctly it will work 🙂 .
 
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I have printed CF-Nylon on my Ender 5. It works pretty well, but you need to print on a G10 buildplate to get good adhesion. The parts are tough but more flexible than PLA. I'm interested in trying the filament that you mentioned in the original post. Thus far, I have had good luck with NylonX.
 
So a team and I are working on a rocket to go to 1 mile in the air and we currently are somewhat in a good stage but I am not sure what to make our fins out of. I am leaning towards 3d printing as I believe it would be the easiest and quickest option. Currently, I have been looking at materials and I am having issues determining what would or would not work. I don't think petg would be strong enough but I'm not sure, unless I find a carbon fiber reinforced option but I'm not sure if that would help. Then there's PA6-cf which has a stronger tensile strength than petg but I wasn't sure if there were other better options at a low price point. This is what I was looking at https://www.amazon.com/Polymaker-PA6-CF-Filament-Carbon-1-75mm/dp/B08T1ZQFKR.
So essentially my question is what has been used by the rocket community in the past when it comes to fins?
According to open rocket, our current design's max speed is 607ft/s and the max acceleration is 175ft/s^2 although that is the best-case scenario.


I don't see an issue with 3D Printing for your application, just use a filament that is strong and has decent temperature resistance. Not from flight, (your rocket is not going MACH 1 or faster) but from heat sitting on the pad in the sun. ...or in the car, but you should take stuff out of the car anyway at the launch site if hot weather especially motors. My filament choice is eSun PRO PLA+ it is almost twice as tough as PETG, easy to print and good temperature resistance. It does not require a heated enclosure like ABS (Which is very good stuff...) Filled filaments like "Carbon fiber" is a waste of time, they are much weaker. You do not gat any strength from the fiber, the prints just look cool. In order to get strength from carbon (or glass) fiber they need to be long strands which would be impossible to print. Those fibers need to be less than 0.4mm long in order to not get clogged up in the nozzle. For fin design, do not design the fins so that any tip, leading or trailing edge thickness is less than 2 x the nozzle diameter or you will have problems printing. The fin can with slots put into it make for near perfect alignment. Example of project I am currently working on: Nike Tomahawk. 2.7" Nike, 1.64" Tomahawk... Still in progress, hope to have it done by Red Glare.

An earlier Nike Smoke I flew had a rather nasty crash due to a CTI reload having a delay 8 sec too long, rocket almost completely destroyed, EXCEPT for the fin can and fins...

Fins snap into the fin can... When glued with 3D Gloop, they are not coming out.

1645115959268.png
 
I don't see an issue with 3D Printing for your application, just use a filament that is strong and has decent temperature resistance. Not from flight, (your rocket is not going MACH 1 or faster) but from heat sitting on the pad in the sun. ...or in the car, but you should take stuff out of the car anyway at the launch site if hot weather especially motors. My filament choice is eSun PRO PLA+ it is almost twice as tough as PETG, easy to print and good temperature resistance. It does not require a heated enclosure like ABS (Which is very good stuff...) Filled filaments like "Carbon fiber" is a waste of time, they are much weaker. You do not gat any strength from the fiber, the prints just look cool. In order to get strength from carbon (or glass) fiber they need to be long strands which would be impossible to print. Those fibers need to be less than 0.4mm long in order to not get clogged up in the nozzle. For fin design, do not design the fins so that any tip, leading or trailing edge thickness is less than 2 x the nozzle diameter or you will have problems printing. The fin can with slots put into it make for near perfect alignment. Example of project I am currently working on: Nike Tomahawk. 2.7" Nike, 1.64" Tomahawk... Still in progress, hope to have it done by Red Glare.

An earlier Nike Smoke I flew had a rather nasty crash due to a CTI reload having a delay 8 sec too long, rocket almost completely destroyed, EXCEPT for the fin can and fins...

Fins snap into the fin can... When glued with 3D Gloop, they are not coming out.

View attachment 505059

Stuff works well. Gloop is great!
 
Do you have a design in mind? I am willing to print a set for you to try.
Thanks for the offer but we do not have a design as of now made and we are still in the testing phase. We did however have our first design review the other day and someone that had been in the program before is currently testing a bunch of different filaments so we are talking to him, hopefully it'll work out.
 
You've not really provided sufficient information for anyone to give you an answer other than you are going to a mile up. Call it 5000ft.
You can achieve that with a G motor or a P motor. A factor of 512 times in thrust Ns available. Also a large difference in physical size. Without the correct parameters for the question, you'll not get the correct guidance for your solution. You've not said what certification you have, so I'm not going to guess what motor you are using.
Without more info you just get GIGO for an answer. Garbage in, garbage out.
Good luck with your project.
 
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