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

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Jose Saura said:
I understand the problems Steve Shannon describes above but I think there might be better ways to address them.

Problem #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.

Building a fin can by hand does not prove the builder has any knowledge about rocketry. All someone has to do is follow simple steps to bind together simple parts. It might help prove the candidate has skills applying epoxy, sawing, using fiber glass, etc. but these skills are as related to rocketry as using a 3D printer. Not that much.

So I think we need to agree on what skills we want to measure and then plan accordingly. To me it would be much more important to evaluate a candidate's ability to stress test a rocket before flying it for example and for the candidate to prove that the rocket passes a series of rigorous tests. For example:
  • Does the shock cord support more that 50x the weight of the rocket?
  • Do the fins support a later force that is n times larger than the mass of the rocket?
  • How much force needs to be applied to the motor mount before it fails?
When using traditional building techniques, it is not easy to perform some of these tests because we only have one rocket and these tests can destroy it. A big advantage of 3D printed models is that we can re-print as many as we need, making it possible to conduct much more rigorous tests and this will in turn produce much better and much safer rockets.

Problem #2. The strength of most 3D printed parts is still not strong enough.
This is simply not correct. There are many materials and many techniques to make very strong 3D printed parts. I have seen many failures of rockets build by conventional methods.

Tripoli and NAR have done an excellent job at helping define safety rules in particular related to where and how rockets should be launched. What I think could help alleviate this concern is to publish an official set of rules, as the examples above, that clearly specify tolerances and testing procedures for different types of rockets. Performing, recording and demonstrating the results of these tests should be a very important step to passing certification for any level, not just L3.

Final comments:
If we want to attract younger generations to rocketry, we need to adapt to new ways of doing things. Banning 3D printing is not going to help so I would like to suggest that we instead embrace the new technology. Rather than worrying about some unethical candidate that does not follow the rules, lets try to create an environment were more people can collaborate on creating and improving rocket designs. To help with this, I have shared my designs online here. It would be great if NAR and Tripoli could work together on enabling collaboration in designing advanced rockets.

If at some point becomes "too easy" to build a fin can, then we should all be happy about that and the best thing is that we will then have time to work on improving other aspects of rocketry such as navigation, instrumentation, recovery, etc. All of these, will help advance the state of rocketry which after all is what we are all trying to do.

Thanks,
Jose Saura
Covington, WA
Click to expand...

I agree 100%!!! As a point I have built a 3d printed Nike Smoke 2.7" Diameter, It flew great three times with high thrust F-Motors (F67 2x, F80 once), Yet someone else's "Conventional Kit" slightly larger, flown with a low thrust G25 shredded the fins off. (It was the Estes Pro line kit) 3D printed fin cans will have more accuracy of alignment, which is getting more important as the size of the rocket and velocity gets higher. I am working on some 3d printed fins right now that are designed to fir a piece of fiberglass sheet inside the fin and sticking out as a fin tab to the motor tube. It is SO much easier to cut fiberglass into rectangular shapes and not have to machine leading edges. Testing with high thrust motors hopefully by May or June. (I hate flying in freezing numb finger weather...lol)
 
beeblebrox said:
I agree 100%!!! As a point I have built a 3d printed Nike Smoke 2.7" Diameter, It flew great three times with high thrust F-Motors (F67 2x, F80 once), Yet someone else's "Conventional Kit" slightly larger, flown with a low thrust G25 shredded the fins off. (It was the Estes Pro line kit) 3D printed fin cans will have more accuracy of alignment, which is getting more important as the size of the rocket and velocity gets higher. I am working on some 3d printed fins right now that are designed to fir a piece of fiberglass sheet inside the fin and sticking out as a fin tab to the motor tube. It is SO much easier to cut fiberglass into rectangular shapes and not have to machine leading edges. Testing with high thrust motors hopefully by May or June. (I hate flying in freezing numb finger weather...lol)
Click to expand...

No all 3d printed fins are the same. A smart “builder” will strengthen then with alternating layers and higher infill percentages.

That being said, I do not like certification with printed or pre-assembled fin cans. Part of the point of the certification process is to learn to build safely. You go around that process when you skip building it.
 
H
cwbullet said:
No all 3d printed fins are the same. A smart “builder” will strengthen then with alternating layers and higher infill percentages.

That being said, I do not like certification with printed or pre-assembled fin cans. Part of the point of the certification process is to learn to build safely. You go around that process when you skip building it.
Click to expand...

How do you figure you are skipping building it? You apparently know nothing about 3d Printing, it is not just art, it is not magic, it takes a lot of skill to design and make a useful item. By your logic, no one should ever use something new. NASA uses 3D printing technology on stuff going into space. Do you think they should not use that on MAN rated equipment? You are worried about using well designed 3D printed stuff on a cert flight where the whole point is success, when people who completed level 3 Cert are flying Christmas trees with M motors...
 
beeblebrox said:
H


How do you figure you are skipping building it? You apparently know nothing about 3d Printing, it is not just art, it is not magic, it takes a lot of skill to design and make a useful item. By your logic, no one should ever use something new. NASA uses 3D printing technology on stuff going into space. Do you think they should not use that on MAN rated equipment? You are worried about using well designed 3D printed stuff on a cert flight where the whole point is success, when people who completed level 3 Cert are flying Christmas trees with M motors...
Click to expand...

I haven't performed a Chandelle or Lazy Eight since my commercial checkride. Yet, these maneuvers are required for certification to show a certain skill and proficiency. Same applies here.
 
beeblebrox said:
H


How do you figure you are skipping building it? You apparently know nothing about 3d Printing, it is not just art, it is not magic, it takes a lot of skill to design and make a useful item. By your logic, no one should ever use something new. NASA uses 3D printing technology on stuff going into space. Do you think they should not use that on MAN rated equipment? You are worried about using well designed 3D printed stuff on a cert flight where the whole point is success, when people who completed level 3 Cert are flying Christmas trees with M motors...
Click to expand...

The “whole point” of a certification flight is not success, but rather to test a person’s knowledge and ability to build a rocket capable of withstanding the stresses that occur with motors in the impulse range available only to people holding that certification.
Once someone designs a successful 3D fin can, someone else can simply 3D print a copy of the file. And that takes less skill than we need our level 3 flyers to demonstrate.
I have no doubt that additive manufacturing techniques will continue to revolutionize many things. But for now, the skills that must be demonstrated in order to certify level 3 are still traditional operations that cannot be bought or downloaded from someone else.
 
Oh, the irony Steve. Kits are by nature designed by others and bought by Cert attemptees no? I'm gonna give Ya a pass though since you're obviously bright enough to add the " traditional" disclaimer ;)...
 
Doesn't level 3 certification require the build to be documented? If the builder is providing evidence that they designed and printed their own fin can doesn't that prove the "person’s knowledge and ability to build a rocket capable of withstanding the stresses that occur with motors in the impulse range available only to people holding that certification?"
 
wsume99 said:
Doesn't level 3 certification require the build to be documented? If the builder is providing evidence that they designed and printed their own fin can doesn't that prove the "person’s knowledge and ability to build a rocket capable of withstanding the stresses that occur with motors in the impulse range available only to people holding that certification?"
Click to expand...
Good point.
 
Obviusly, since a
t least I personally have no intention of printing my Cert attempt fin can, I'm just playing Devil's advocate..
 
Wallace said:
Oh, the irony Steve. Kits are by nature designed by others and bought by Cert attemptees no? I'm gonna give Ya a pass though since you're obviously bright enough to add the " traditional" disclaimer ;)...
Click to expand...

I appreciate your giving me a pass, but please notice I said certification was about building, not design. [emoji3526]
 
Last edited:
Steve Shannon said:
I appreciate your giving me a pass, but please notice I said certification was about building, not design.
Click to expand...

But if somebody is building something other than a concrete donkey that will fly low and slow then knowing about the various mechanical design criteria and limitations becomes a necessary evil, or the probability of failure is increased.

I think this is not a one-size-fits-all discussion. The TAP is allowed to evaluate the proffered design and rocket. The TAP is also allowed to request help from other people if they decide that their knowledge is insufficient to evaluate certain parts of the rocket.
 
I have recently seen Kevlar 3D printing that is insanely strong. I think this is a direction that needs to be incorporated and I hope to test it. The bottom line is the BoD is doing risk management so please send them your data if anyone has any. This would help make criteria to manage risk and ensure safety. I do not agree with the "build" idea as stated earlier the use of kits for certification. I personally love kits as they allow for better building practices that maybe otherwise cost prohibited.
 
OverTheTop said:
But if somebody is building something other than a concrete donkey that will fly low and slow then knowing about the various mechanical design criteria and limitations becomes a necessary evil, or the probability of failure is increased.

I think this is not a one-size-fits-all discussion. The TAP is allowed to evaluate the proffered design and rocket. The TAP is also allowed to request help from other people if they decide that their knowledge is insufficient to evaluate certain parts of the rocket.
Click to expand...

You’re right; I don’t mean to imply that design is unimportant. The candidate must understand enough about design to assess whether a kit is suitable for use or what modifications are necessary to make it work.
What I’m trying to say is that a design can be excellent, but without correct execution it can become an unsafe flight.
There are lots of opportunities to demonstrate 3D fin cans on smaller rockets. As we all learn more I’m sure the board will revisit the matter, but there will always be a need to demonstrate that a person can build rockets using more traditional materials and skills.
 
Steve Shannon said:
As we all learn more I’m sure the board will revisit the matter, but there will always be a need to demonstrate that a person can build rockets using more traditional materials and skills.
Click to expand...

I think it makes more sense if the board just says we don't feel that our TAPs currently have enough knowledge and experience when it comes to 3D printing to evaluate the design and build of the rocket being presented for certification.

Why will there always be a need to demonstrate that a person can build using traditional materials??? In some future time when 3D printing is permitted if you can print a rocket that can withstand the forces of flight from L3 class motors then why would you have to show you can build with traditional materials and skills??? It's as if the board is saying that they don't recognize the ability to 3D print as a skill. I think that's just ignorant. Getting quality prints is definitely not an easy thing to do and certainly requires skill and in-depth knowledge.
 
beeblebrox said:
NASA uses 3D printing technology on stuff going into space. Do you think they should not use that on MAN rated equipment?
Click to expand...

Yes - NASA and other aerospace firms have adopted several forms of additive manufacturing. They have also spent many hundreds of millions of dollars characterizing the material allowables and developing a design system to use them. I can see that asking builders, TAPs & RSOs to sign off on something without that kind of data on top of a cert flight that is already pushing the envelope for someone might be a bit much.

I can also understand the desire to certify someone on traditional build methods. The same way I doubt an FAA examiner would let me fly a checkride approach on autopilot even if by modern standards its a more reliable and safer method. They've defined a set of skills that are required and that's what they want to see.
 
wsume99 said:
I think it makes more sense if the board just says we don't feel that our TAPs currently have enough knowledge and experience when it comes to 3D printing to evaluate the design and build of the rocket being presented for certification.

Why will there always be a need to demonstrate that a person can build using traditional materials??? In some future time when 3D printing is permitted if you can print a rocket that can withstand the forces of flight from L3 class motors then why would you have to show you can build with traditional materials and skills??? It's as if the board is saying that they don't recognize the ability to 3D print as a skill. I think that's just ignorant. Getting quality prints is definitely not an easy thing to do and certainly requires skill and in-depth knowledge.
Click to expand...

I'm sure that eventually it will be possible to buy a "complete" kit that requires only attachment of some screws and quick links to be L3 ready.
I, for one, took the easy way out and purchased a kit; but still required a few months of planning and build time. Looking back, I have much more respect for those that scratch-built and even sometimes wish that I had too.
 
I am not talking about purchasing a printed kit to assemble. I am talking about someone who prints their parts on their own and assembles them.
richP said:
I'm sure that eventually it will be possible to buy a "complete" kit that requires only attachment of some screws and quick links to be L3 ready.
I, for one, took the easy way out and purchased a kit; but still required a few months of planning and build time. Looking back, I have much more respect for those that scratch-built and even sometimes wish that I had too.
Click to expand...
 
wsume99 said:
I think it makes more sense if the board just says we don't feel that our TAPs currently have enough knowledge and experience when it comes to 3D printing to evaluate the design and build of the rocket being presented for certification.

Why will there always be a need to demonstrate that a person can build using traditional materials??? In some future time when 3D printing is permitted if you can print a rocket that can withstand the forces of flight from L3 class motors then why would you have to show you can build with traditional materials and skills??? It's as if the board is saying that they don't recognize the ability to 3D print as a skill. I think that's just ignorant. Getting quality prints is definitely not an easy thing to do and certainly requires skill and in-depth knowledge.
Click to expand...

The BoD most certainly recognizes the ability to 3D print as a skill. That doesn't necessarily mean that it is a skill sufficient (at this time!) to be trusted universally in a Level 3 flight.

No doubt getting quality prints is not easy, but can the members of the TAP all distinguish between a 3D print that's just not strong enough and one that is? Good thing I'm not on the TAP because I couldn't distinguish between the two.

There's also the issue of having a friend with more skill than me, printing my fin can.

The need to demonstrate traditional skills may not be there indefinitely. Things change. But until the issues with 3D printing can be resolved -- and this discussion wouldn't be taking place if there were no issues -- the BoD is doing what is managing risk. And that is best, ultimately, for the organization as a whole (and not just 3D printing enthusiasts).

Best -- Terry
 
"It's OK, I'm a Limo driver!!"

Frankly, I'm a little frustrated with the proliferation of 3D printing, and people think it's the absolute replacement for plastic (and other) parts..

Would I trust a competent engineer, with a structural background, and a fin can from a Markforged printer, with inlaid reinforced filaments, sure. Would I trust the same fin can, designed by a 22yr old barista and printed on the library's 3D printer? No. (and what's to say the Barista didn't just download the fin can & scale it up to suit his BT?!)

Building it, referring to using established & known methods and chosen & known materials, that are known to have certain characteristics & yield certain results. There is then no guess work or speculation for the judges.



(the boss & I went o see a Markforged printer late last year. Sweet printer! Sweet price to go along with it!!!)

https://markforged.com/mark-two/?mf...MI6v_dt8325gIVmZOzCh0UVAKAEAAYASAAEgIicvD_BwE
 
flown already on a 98mm L1500
name of rocket is director's demise


wjAqIHzfiXzLrKc62oLjIj_FiUcSVrWak3k1QdB2HpFaeXRP6wiJM1seOecO8L5-l4e9brtxJKcqIhsSzeyPoOqN2FoS5hlzviaONBQyWr81A11QDH1gzF-8n3M5npJg-eSOR47splJq2r8JQqfYOn7qFyDU_QK3hVO-ZwJdY2Nvg7stIZyhpuAjm7mA4CCgXGelurfN5YbvXI1WJgH1-iKCV_pp7rAJG-wQicRDKPq_iMlZv-zDzRzjKuD_ZzJtlAISGXEvZlCXeCoSNt38TRxS8Ru9XewrjNpqtgm7uje2u2OjY3Y0o5PDkjr4iDOAgp287vhYiC5Xy0u7LiavB06fULPNY0fXk_4Br8cN4tVqSELyR8RAl7CJxeslDcyOu2lJMa6EkEgHKGBduGIY1p6-uYyOfsRhu5ShlJ1RGmw0i-ccUnOsRjIhWoi0MvHHSE18LAc2_ERI3fQbQ1dZeNJ263bSlc5HyTmt0LQqTGeHxrjxMK1V0LvdK2J_UxKiR1sP2GaQKm0upQVQlGkyrXUnl3uDa4sO4_E8bbEKDvtKTlMRgGyz_e8utccYOgrqlc5aVMF35LmxUX971jfkVA2HPDo3dSw14uCRo7Ij8jQtXNtlzsbHpkvPFi_4ZpUNr9Jq9l5ZoUno8E90RsYhB6pdldHwCVgQJXCyigF-yBT057CbMTI_Rw8=w1085-h1928-no
 
I remember the same type of argument at my local camera club:

Do we allow 'digital' cameras & photos?! (this was about 18 years ago.. when the first DSLRs were coming to market..) this was a big debate..

And recently the same for "I-phone" pictures.. this was a relatively short debate, as per the initial "digital" challenge.

3D printing is still new, and still somewhat unreliable / data insufficient..
 
Nytrunner said:
And Experiments like Jbr's above are what we need more of.
Obey the rule, don't use it on a cert flight, submit more data. Tripoli is reasonable. This will pass in time
Click to expand...
Exactly, a well documented series of data points goes a long way toward proving the viability and proper usage of new technologies.
 
dr wogz said:
"It's OK, I'm a Limo driver!!"

Frankly, I'm a little frustrated with the proliferation of 3D printing, and people think it's the absolute replacement for plastic (and other) parts..

Would I trust a competent engineer, with a structural background, and a fin can from a Markforged printer, with inlaid reinforced filaments, sure. Would I trust the same fin can, designed by a 22yr old barista and printed on the library's 3D printer? No. (and what's to say the Barista didn't just download the fin can & scale it up to suit his BT?!)

Building it, referring to using established & known methods and chosen & known materials, that are known to have certain characteristics & yield certain results. There is then no guess work or speculation for the judges.



(the boss & I went o see a Markforged printer late last year. Sweet printer! Sweet price to go along with it!!!)

https://markforged.com/mark-two/?mf...MI6v_dt8325gIVmZOzCh0UVAKAEAAYASAAEgIicvD_BwE
Click to expand...
I actually decided AGAINST using a markforged for my minimum-diameter 3D printed rocket (you might remember it from the November CRMRC launch - the I205 powered rocket I never found again) for a couple of reasons. In order to inlay the fiber reinforcements, the parts have to be sufficiently thick for a fiber run both out and back, along with a sheath of the more conventional FDM filament around it. This makes it impossible to print a fully-formed fin can with reinforcements unless you use very thick fins. Also, the nylon or Onyx (proprietary, but like 80% nylon) filaments are significantly more flexible than PLA, to the point where fin flutter was a major concern on the markforged printed parts, but was not a problem at all on the parts I ended up flying, which were made from PLA on a Prusa. The one major advantage that the markforged has for airframe components in HPR is that nylon has a much higher glass transition temperature than PLA, ABS, or PETG, though this can be largely alleviated with primer and paint to give a bit of a dissipative layer over the more temperature sensitive components.

I plan to refine that design I flew last November (that really was a proof of concept where I was very concerned about thermals - hence the lack of an onboard tracker, I didn't want to risk losing it if there was a thermal failure), and eventually perhaps scale it up to a 38mm minimum diameter rocket. If there's interest I can throw up a thread documenting the project - there's some interesting thermal and structural analysis of 3D printed components at transsonic and supersonic Mach number I could share with everyone.
 

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