Tripoli prohibition on the use of 3D printed fin cans for L3 certification

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3D printed nose cone launches on a Loki L1482 to 3200 feet, 725 mph
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As a data point, here is a flight of one of my rockets with 3D printed fins:



I didn't have an altimeter on this flight, but OpenRocket was predicting around 430-440 mph. The fins are thicker than they would have been with other materials, but they can be made to work if you take the material properties into account.
 
Ez2cDave said:
Cool . . . Now, what about 3-D printing those identical Fins and duplicating the flight ?

Dave F.
Click to expand...

That's not a fair comparison. Anyone even remotely familiar with 3D printing knows that you cannot just copy something that is made of different material and expect it to act the same. In the case of 3D printed fins, I have personally designed fins that had carbon fiber rods epoxied into them to make them extremely strong and withstand up to mach .8 on a J motor so far (my L2 rocket). I'm confident that they would survive mach 1+ flights due to their profile and strength, a claim that I plan to put to the test soon. This is the type of modifications that have to be taken into consideration when creating 3D printable fins as it's critical to know the limits of your materials.

I agree that 3D printed fincans on L3 flights should be restricted to those existing L3 certifications as they have proved their competency and are at their own liberty to take risks (as long as it does not endanger the health of others). I hope to see people pushing the technology to its limits and coming up with new methods and techniques to make 3D printed parts comparable to their counterparts. People need to think through their designs as many 3D printed parts have a severe weakness when manufactured incorrectly such as printing in the wrong orientation, too thin of walls, etc. 3D printing is an art, never assume that you know everything or your design will fail is a way that you never saw coming.
 
Ben Martin said:
That's not a fair comparison. Anyone even remotely familiar with 3D printing knows that you cannot just copy something that is made of different material and expect it to act the same. In the case of 3D printed fins, I have personally designed fins that had carbon fiber rods epoxied into them to make them extremely strong and withstand up to mach .8 on a J motor so far (my L2 rocket). I'm confident that they would survive mach 1+ flights due to their profile and strength, a claim that I plan to put to the test soon. This is the type of modifications that have to be taken into consideration when creating 3D printable fins as it's critical to know the limits of your materials.

I agree that 3D printed fincans on L3 flights should be restricted to those existing L3 certifications as they have proved their competency and are at their own liberty to take risks (as long as it does not endanger the health of others). I hope to see people pushing the technology to its limits and coming up with new methods and techniques to make 3D printed parts comparable to their counterparts. People need to think through their designs as many 3D printed parts have a severe weakness when manufactured incorrectly such as printing in the wrong orientation, too thin of walls, etc. 3D printing is an art, never assume that you know everything or your design will fail is a way that you never saw coming.
Click to expand...

Exactly! Thank you!
 
Ez2cDave said:
Steve,

You posted, "However, for two reasons the board has decided to prohibit the use of 3D printed fin cans for Level 3 certification flights. The two reasons are:

1. It’s impossible to know whether the L3 candidate designed the fin can. Simply printing a shared file doesn’t demonstrate expertise or knowledge, which is what certification represents.

2. "The strength of most 3D printed parts is still not strong enough."

I have a few genuine questions : ( no "sneer quotes" )

(1) "Designing" the fin can . . . What if a flyer can prove that he did "design" it, even if it was made by someone else ? Also, the 3D printer actually "makes" things, not the flyer.

(2) A shared 3D file is essentially the same as ordering components ( not designed or made by the flyer ).

From Tripoli: "Commercially available pre-fabricated fin cans, either as part of a kit or obtained separately, may not be used for level 3 certification flights."

Shared 3D files and the subsequent printed items, made later, are not "pre-fabricated" . . . Does that give them a "loophole" ?

(3) If a flyer uses a kit, he did not design it or make the components, should kits be disallowed for Cert flights ?

(4) If the strength of most 3D printed components are not strong enough, in the interest of safety, why should their use be allowed, at all ?

Frankly, your statement, "The strength of most 3D printed parts is still not strong enough", should have been reason enough to prohibit their use, based on the safety risks alone, and not just in Cert flights !

In my opinion, I think that "plastic" fins ( as "fin cans" or individual components ), as produced by current "home 3D technology", are inherently prone to failure, especially in the upper Total Impulse ranges, and at supersonic velocities. I think that a much closer analysis and, possibly, some form of structural testing is in order, to provide accurate data, in the interest of safety.

Dave F.
Click to expand...

As a TAP I do not need or require a rule to determine the suitability of construction materials used in L3 cert projects. For the record, I have not experienced any individuals considering the use of 3D printed structural parts in their L3 cert project.

Reason 1 in the TRA BOD decision is a non starter, as proving a fin design or any part of a project is negated by the proliferation of ready made parts kits with a totally designed rocket, only requiring assembly of the designed parts into a acceptable L3 project.

Reason 2 may be correct to some extent. However, lets say an individual designs a 3D printed fin can and then as part of the construction design covers the entire fin can with a carbon fiber/composite process. Sounds far fetched? I think not.

IMO, we have generated a solution in search of a problem. The guidelines we, as TAP, have been using for many years, IMO, is all I need to guide me as TAP in making decisions and guiding a L3 candidate through the L3 certification process and that includes; " quashing the use of marginal design and construction materials of any type". Sometimes, I believe some folks just have a hard time saying no and if there is a rule forbidding something, it releases them from having to make the hard decisions that comes with the territory...

I did count to 20 before I'm hitting the post reply button...
 
Ben Martin said:
That's not a fair comparison. Anyone even remotely familiar with 3D printing knows that you cannot just copy something that is made of different material and expect it to act the same. In the case of 3D printed fins, I have personally designed fins that had carbon fiber rods epoxied into them to make them extremely strong and withstand up to mach .8 on a J motor so far (my L2 rocket). I'm confident that they would survive mach 1+ flights due to their profile and strength, a claim that I plan to put to the test soon. This is the type of modifications that have to be taken into consideration when creating 3D printable fins as it's critical to know the limits of your materials.

I agree that 3D printed fincans on L3 flights should be restricted to those existing L3 certifications as they have proved their competency and are at their own liberty to take risks (as long as it does not endanger the health of others). I hope to see people pushing the technology to its limits and coming up with new methods and techniques to make 3D printed parts comparable to their counterparts. People need to think through their designs as many 3D printed parts have a severe weakness when manufactured incorrectly such as printing in the wrong orientation, too thin of walls, etc. 3D printing is an art, never assume that you know everything or your design will fail is a way that you never saw coming.
Click to expand...

Ben,

The thread is clearly not about 3-D printed Nose Cones . . . Yet, that is where you took it. Clearly, talking about 3-D printed Nose Cones is not a fair comparison to 3-D Printed Fins.

QUOTE : "People need to think through their designs as many 3D printed parts have a severe weakness when manufactured incorrectly such as printing in the wrong orientation, too thin of walls, etc. 3D printing is an art, never assume that you know everything or your design will fail in a way that you never saw coming." END QUOTE:

What sources of public information are readily available to teach people how to safely make 3-D printed rocket fins up to, and including, Level 3?

How is the "correct orientation" determined and what sources of public information are readily available to teach people ?

By your own admission, in the last sentence of your quote, you seem to imply that 3-D printing is a less reliable method, with multiple failure modes possible . . . That, alone, should make it abundantly clear that, for most people, when it comes to 3-D printing HPR fins, the risks clearly outweigh the benefits, at this point in time !

Dave F.
 
Ez2cDave said:
Ben,

The thread is clearly not about 3-D printed Nose Cones . . . Yet, that is where you took it. Clearly, talking about 3-D printed Nose Cones is not a fair comparison to 3-D Printed Fins.

QUOTE : "People need to think through their designs as many 3D printed parts have a severe weakness when manufactured incorrectly such as printing in the wrong orientation, too thin of walls, etc. 3D printing is an art, never assume that you know everything or your design will fail in a way that you never saw coming." END QUOTE:

What sources of public information are readily available to teach people how to safely make 3-D printed rocket fins up to, and including, Level 3?

How is the "correct orientation" determined and what sources of public information are readily available to teach people ?

By your own admission, in the last sentence of your quote, you seem to imply that 3-D printing is a less reliable method, with multiple failure modes possible . . . That, alone, should make it abundantly clear that, for most people, when it comes to 3-D printing HPR fins, the risks clearly outweigh the benefits, at this point in time !

Dave F.
Click to expand...

I don't mean to be rude, but when did I ever mention 3D printed nosecones? I mentioned my experience with 3D printed FINS and the design considerations that I took into account. I'm sure there's a lot of information on the internet on how to print strong 3D objects, but that was not my point. Every method has its failure modes, such as using wooden fins with the grain going vertically instead of horizontally. This is similar to how you want to arrange the layers on a 3D printed fin as the forces could delaminate the vertical layers. For my fins, I printed them with vertical layers as I knew that the epoxied carbon fiber rods would provide the layer adhesion needed for the stress of flight. On my 3D printed fincan (https://www.thingiverse.com/thing:3246140), the fins are printed with the horizontal layers, meaning that they will not shear off during flight.

Every construction method has its flaws, from incorrect surface prep to manufacturing defects. It is up to YOU to safely construct your rocket, using available resources such as this forum to ensure that it can survive the stresses of flights with ease. I agree that 3D printing has its flaws, but you act like there are no failures other than those involving 3D printed components. As I stated before, I look forward to people such as myself experimenting with the technology and finding new methods to apply it to rocketry. Start small and start to scale up your concept and expand upon it as you go, it's the best way for the risks and benefits to be acknowledged.
 
Ben Martin said:
That's not a fair comparison. Anyone even remotely familiar with 3D printing knows that you cannot just copy something that is made of different material and expect it to act the same. In the case of 3D printed fins, I have personally designed fins that had carbon fiber rods epoxied into them to make them extremely strong and withstand up to mach .8 on a J motor so far (my L2 rocket). I'm confident that they would survive mach 1+ flights due to their profile and strength, a claim that I plan to put to the test soon. This is the type of modifications that have to be taken into consideration when creating 3D printable fins as it's critical to know the limits of your materials.

I agree that 3D printed fincans on L3 flights should be restricted to those existing L3 certifications as they have proved their competency and are at their own liberty to take risks (as long as it does not endanger the health of others). I hope to see people pushing the technology to its limits and coming up with new methods and techniques to make 3D printed parts comparable to their counterparts. People need to think through their designs as many 3D printed parts have a severe weakness when manufactured incorrectly such as printing in the wrong orientation, too thin of walls, etc. 3D printing is an art, never assume that you know everything or your design will fail is a way that you never saw coming.
Click to expand...

Concur, this is my point exactly. Not all 3D printed fincans are the same. With most 3D printed parts, it takes sustained head to make them fail if they are printed with PETG or an exotic filament. I would never recommend a cert flight occur with 3d printed fin can.
 
Ez2cDave said:
Hi, Chuck !

Nose Cones are not as much of a problem, except at MACH+ velocities. Even then, an aluminum tip would probably provide adequate protection for "most" flights.

The issue here is Fins, due to their inherent thinness, possibility of flutter, softening with heat, and possible shattering, if brittle.

Dave F.
Click to expand...

You need to read the whole thread.

I know the main thread was initially about fin cans, but someone brought up all the failures of nose cones. I was pointing out nose cones as an example. If you can print one not to melt and fail, fins will only take a matter of time.
 
TurbulentSphere said:
As a data point, here is a flight of one of my rockets with 3D printed fins:



I didn't have an altimeter on this flight, but OpenRocket was predicting around 430-440 mph. The fins are thicker than they would have been with other materials, but they can be made to work if you take the material properties into account.
Click to expand...

Didn't even appear to wiggle. How and with what are those fins attached? Almost looks like you printed the fillets Too? Whatever methods you decided on it obviously works.
 
Wallace said:
Didn't even appear to wiggle. How and with what are those fins attached? Almost looks like you printed the fillets Too? Whatever methods you decided on it obviously works.
Click to expand...
Yep, the fillets are printed on. There is a line of countersunk holes running down each fillet and the fins are bolted into the motor mount (which is also 3D printed). I hate messing with glue and now I can replace them if they break.
 
Wallace said:
Didn't even appear to wiggle. How and with what are those fins attached? Almost looks like you printed the fillets Too? Whatever methods you decided on it obviously works.
Click to expand...

If done right, they are perfectly straight and perfect fillets. Some require slight sandings to remove fur.
Wallace said:
Didn't even appear to wiggle. How and with what are those fins attached? Almost looks like you printed the fillets Too? Whatever methods you decided on it obviously works.
Click to expand...

That is the beauty of 3D printed fins is that you can easily print the fillets into the product. Complex shapes are breeze.
 
I was included in the pre-announcement discussions regarding the use of raw 3D fin cans and support the decision that they shouldn’t be an option for L3 certification flights. As a TAP or L3CC you can look at the plywood or G-10 fins of a project and use your historical experience as to the viability of the construction. With the myriad of printing materials and production options that critical flight worthiness analysis is diminished. The L3 certification flight is being flown under the TAP/L3CC members HPR certification, and as such should something go wrong we become part of the liability chain.

Perhaps more important, using a 3D printed fin can for a L3 certification flight moves the construction challenge closer to that of a RTF airframe. I just don’t think that is the direction we should be going with certification flights. After a flier’s successful certification flight, they should have the opportunity to explore alternative construction methodologies and the announced decision allows this to occur.
 
Last edited:
cwbullet said:
Hoe did they fail? I think nose cones would not fail often if they are printed with the right material and with the right infill. I have had one rocket fail with 3D printed parts. I made a BT60 rocket with a fin can and nose cone. It flew great with an F so I got brave and flew it with a G or H. The rocket flew to pieces after the body tube bent. The nose cone and fin can survive to fly again despite a hard landing.

The key to a successful 3D printed rocket for high power is the material you use to print it with and the infill. You would be foolish to use PLA, but ABS or PETG with CF should hold up to most G-J motors with the right infill.
Click to expand...

I just purchased a 3D printer two weeks ago, and with help from a friend of mine who is an expert in the field (He routinely tests new printers for manufacturers before they are marketed...) helped me set up the thing (Ender 3 Pro) and gave me about $150 of filament for free. Since I had time, and a launch coming up I HAD to make some rocket parts... Frank Perdue said "Parts is Parts" I only had PLA to work with, I built two Nike Smoke sounding rockets with 3D printed fin cans, fins and nose cone. Cost to build both <$10 For the first one using the files I found online for the model, I substituted BT-55 for the printed body tube. The fins were spiral vase printed and cast solid with Tap Plastics marine epoxy. The Fin Can was printed with 1mm walls with 100% infill. (Has deep sockets for the fins to glue into) Nose cone printed the same way. (File set designer recommended and designed all the parts for vase mode, I realized they would be too weak printed that way.) Rocket flown with my own research motor, C8-6. Second one, 203% upscale, fins printed with 100% infill, fin can and nose 2mm walls with 100% infill. Nose printed in three pieces, minimum number due to height limitation of printer. The extra material for intersection bases for the nose added the necessary mass for proper CG balance. Body tube was US Rockets 2.7" host mount tube which is a little heavier wall than standard LOC or AeroTech 2.6" tube. Flown with a New AeroTech F67-9 the flight was perfect. Next flight planned will be with an H135... Note: Someone else flew an Estes Proline Nike Smoke with a G80, the fins shredded off...F67_Nike_Smoke.jpg Nike Smokes.jpg
 
Here's a video of the first flight of my 3D printed fincan design. It shows that if done correctly, 3D printed fincan provide unrivalled stability in flight (comparing to traditional). I plan on stressing the design with larger motors every flight, I'm pretty confident it will survive.

Link:

I love the activity on this thread, shows how exciting this "new" technology is and the many ways it can be applied to rocketry.
 
TurbulentSphere said:
Yep, the fillets are printed on. There is a line of countersunk holes running down each fillet and the fins are bolted into the motor mount (which is also 3D printed). I hate messing with glue and now I can replace them if they break.
Click to expand...

Was the spin intentional ?

If not, I am surprised that 3-D printing didn't provide perfect fin alignment.

Dave F.
 
Ez2cDave said:
Was the spin intentional ?

If not, I am surprised that 3-D printing didn't provide perfect fin alignment.

Dave F.
Click to expand...

Whoops thought you quoted mine. But it probably spun due to a slight misalignment of the fins through the structure. That's why single 3D printed fincan provide the least amount of roll.
 
Steve Shannon said:
At our monthly BoD meeting we discussed the proliferation of 3D printing. We all agree that the technology is exciting and will undoubtedly lead to some great designs. However, for two reasons the board has decided to prohibit the use of 3D printed fin cans for Level 3 certification flights. The two reasons are:
1. It’s impossible to know whether the L3 candidate designed the fin can. Simply printing a shared file doesn’t demonstrate expertise or knowledge, which is what certification represents.
2. The strength of most 3D printed parts is still not strong enough.

The board has not prohibited the use entirely. We would like it if actual launch experience with 3D printed fin cans gets reported so we can better understand what the risks are from this technology. Our L3 certification procedure will be updated with this prohibition.
Thanks,
Steve
Click to expand...
Steve, if you print a fincan as the base and laminate it with CF of FG, would that be acceptable or no?
I agree with the decision but 3d printing is great for base components and then lamination can make them much stronger and demonstrates skill and knowledge if done correctly, though I can see issues with not having through the wall attachment of the fins.
 
Ben Martin said:
Here's a video of the first flight of my 3D printed fincan design. It shows that if done correctly, 3D printed fincan provide unrivalled stability in flight (comparing to traditional). I plan on stressing the design with larger motors every flight, I'm pretty confident it will survive.

Link:

I love the activity on this thread, shows how exciting this "new" technology is and the many ways it can be applied to rocketry.
Click to expand...


Ben,

Now, THAT is the kind of precision alignment I would expect to see from a 3-D printer !

I'm not "Anti-3D printing", but I think that a lot more rocketry-specific information needs to be made publicly available to Rocketeers, particularly regarding methods, design, and materials.

Dave F.
 
Ez2cDave said:
Wallace,

Those parts are not manufactured using 3-D printer technology.

3-D-printed components, particularly relatively thin, flat cross-section items, such as fins are known to have less structural strength and be prone to thermal weakening.

The materials they are using have already been tested by years, if not decades of use. Their inherent reliability is already quantified.

Ask yourself these questions :

(1) Is a plastic, 3-D printed fin as strong as . . . ?

(a) A Fiberglass fin of the same thickness.
(b) A Carbon Fiber fin of the same thickness
(c) An Aircraft Plywood fin of the same thickness
(d) An Aluminum fin of the same thickness

(2) Is a plastic, 3-D printed fin as resistant to thermal deformation as . . . ?

(a) A Fiberglass fin of the same thickness.
(b) A Carbon Fiber fin of the same thickness
(c) An Aircraft Plywood fin of the same thickness
(d) An Aluminum fin of the same thickness

(3) What changes to a plastic, 3-D printed fin would needed to make it as strong, and as thermally-stable as . . . ?

(a) A Fiberglass fin of the same thickness.
(b) A Carbon Fiber fin of the same thickness
(c) An Aircraft Plywood fin of the same thickness
(d) An Aluminum fin of the same thickness

Final thought : With safety being paramount in Rocketry, why would anyone, in good conscience, choose to use a sub-standard method or sub-standard materials and risk an accident ?

Dave F.
Click to expand...

There is no reason to be so negative, new technologies need to be viewed as that. Just because something is new does not make it Sub-Standard. There are many uses. I used PLA for some parts on my L2 cert rocket I flew yesterday because it was what I had available. I needed a switch ring for the payload bay, Ever try to cut a perfect ring out of a 5.56" LOC tube? The 3D printed ring I made not only was perfectly sized and square but also gave me exact spacing for the air vent holes to the AV Bay. Also the part was not structural anyway. My altimeter was attached to the AV Bay backbone with a PLA printed sled. The rocket was in the Hot June sun for over 1/2 hour, no degradation of parts was noted. Nose cone was standard LOC cone, Fins were 1/4" Plywood... PLA however is slightly stronger than Aircraft plywood. PLA 37MPa - 5366PSI, Ply 34.5MPa - 5003PSI ABS is 27MPa, 3916PSI. An advantage of 3D printing is exacting control over dimensions, Fins can be designed more accurately, and be made in a manner to be re-enforced on the inside. Example, you could design a pocket in the 3D printed fin to accept a fiberglass rectangular tab that bonds thru the wall to the motor mount tube. This could be applied to a properly designed fin can. The moral of the story is, Don't ban something you don't fully understand: embrace, adopt and improve it!
 
Charles_McG said:
What do you use with PETG?

And not being an L3 flier, what’s so different between a 10G J boost and a 10G M boost? Torque and lateral forces on components because the parts are bigger?
Click to expand...

The difference is in the thrust profiles of the motor and the masses of the rocket. A 10 gee boost from a J motor is probably pushing a 10 or so pound rocket. A 10 gee M boost is pushing at least a 30-50 pound rocket. I have not looked at all motors, but generally with M motors you can expect to see significantly more average thrust and significantly more maximum thrust. I am using a Loki M2550 for my L3 which has an average thrust of 670 pounds. The J530 from CTI produces just under 125 pounds of average thrust and just over 175 pounds of maximum thrust. Force=(Mass)(Acceleration)

The torque and lateral forces are also going to be much higher because the components are bigger, just like you said as well. The taller the fin the more leverage it has, so the more you need to reinforce it.
 
Last edited:
Binder Design said:
Slight flutter at max q.
Click to expand...
I think that was the camera shaking due to a shotty tape job. The next flight I will be screwing the camera to the body tube so I'll see if it's really fluttering. With your fincan you really don't have to worry about fluttering anywhere close to these speeds, but it's also a lot more expensive than $5 in filament.
 
Ben Martin said:
With your fincan you really don't have to worry about fluttering anywhere close to these speeds, but it's also a lot more expensive than $5 in filament.
Click to expand...

Understood, and not meant as a slight to printed fin cans. I'm developing my own composite filament and single purpose printer for high temperature printing.
 

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