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

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OverTheTop said:
Fair enough. But done correctly, and the RSOs can partly help weed out the duds, it can be a safe and acceptable solution.

Remember too, that having a failure at altitude can be a risk-mitigating strategy, with appropriate recovery system design.
Click to expand...

Define "done correctly" . . .

What sources of public information are available to teach Rocketeers how to "do it correctly", when it come to 3-D printed fin design on subsonic, transonic, and supersonic rockets ?

Who is going to train the RSO's in proper 3-D Fin design ?

Dave F.
 
OverTheTop said:
How I would do it ;).

Seriously though, a knowledge of material properties and a reasonable process can get you to an acceptable outcome. It isn't a simple "She'll be right if you do this" sort of thing.
Click to expand...

Okay . . . How does the average Rocketeer gain that particular knowledge and learn a reasonable process ?

What are the sources of information ?

Dave F.
 
OverTheTop said:
Fair enough. But done correctly, and the RSOs can partly help weed out the duds ...
Click to expand...

The problem with this, is that probably most RSO's also lack experience with 3DP fins on large rockets. Checking a cg / cp relationship on a certification flight is relatively easy. Having the flier explain his thrust to weight ratio is relatively easy.
If finished and painted, it may not even be immediately obvious to an RSO that a rocket has 3DP fins. And again, we are only talking about L3 certification flights, not a general ban on new tech altogether.
 
gldknght said:
The problem with this, is that probably most RSO's also lack experience with 3DP fins on large rockets. . . .

And again, we are only talking about L3 certification flights, not a general ban on new tech altogether.
Click to expand...

Yes, who "trains" the RSO's ?

For that matter, who "trains" the Rocketeers how to "do it right" ?

There are no Rocketry-specific sources of information available, regarding the use of "proper" materials, "proper" 3-D Printer settings, or internal structure of large 3-D printed Fins. So, how does the average Rocketeer, who just plunked down his cash for a 3-D printer, and is a total Newbie, gain this much-needed Rocketry-specific information ?

As for L3 Certification flights, I think it would be fair to say that, at this time, the ban relates only to that. However, if 3-D printed Fins and Fin Cans start failing in sufficiently large numbers ( TBD by TRA / NAR ), or there is a major accident or numerous minor accidents, look for that Ban to expand quickly !

Dave F.
 
and how do you know that 1 layer of FRP is plenty?
or do you need 3 or 5 or 10?
how do you know that cardboard or other materials will stand up to an M?
there have been plenty of cardboard M rockets

don't be like AOC and just say things that you don't have a clue about with no supporting data
 
jbr said:
so Dave, looks like this statement goes along with ALL fins no matter what material they are made from, not just 3DP ones

and there is info ALL over the web, here is one

https://airwolf3d.com/2018/03/20/material-strength-testing/
Click to expand...

Show me something HPR-Rocketry specific . . . That website is not for Newbies in 3-D printing.

As for other materials ( Balsa, Basswood, Plywood, Fiberglass, Carbon-Fiber, etc ), they have been proven over time, unlike 3-D materials ( there are so many different kinds ) in HPR Rocketry Fin applications. Just because a few people can do it, does not mean that all people can do it safely.

Rather, than "putting it back on me", why not provide links to information that is appropriate to the questions at hand ? Namely, specific, Rocketry-related websites with tutorials, etc. ?

Simple answer, in my opinion, is that you don't do that because there are no HPR-specific 3-D printing websites, yet. So, without any reliable method of learning proper techniques. materials, and designs, most Rocketeers are operating in "Print & Pray" mode, "rolling the dice" on safety on every flight !

As for "AOC", I am diametrically-opposed to her and those with like opinions. I am ASKING FOR HPR Rocketry-specific,"supporting data", not a bunch of "techno-speak" from a commercial 3-D printing website !

Dave F.
 
and you have to understand with technology this new, there is a lot of IP, and they don't post due to that
 
jbr said:
and how do you know that 1 layer of FRP is plenty?
or do you need 3 or 5 or 10?
how do you know that cardboard or other materials will stand up to an M?
there have been plenty of cardboard M rockets

don't be like AOC and just say things that you don't have a clue about with no supporting data
Click to expand...


I think the point here is, if you don't know whether xxx material will hold up to the stresses of your flight, that material should not be used in your certification flight.

I know that reinforced fins will hold up because others have proved it before me. I know that I needed to add expandable foam to my L3 nose cone based on other's experience. Also, I learned a lot of things on my L1 and L2 projects that will be useful on my L3.

I think that's what Tripoli is saying with this restriction, that more testing is needed and a developed set of guidelines established so the L3 cert flier can show his/her 3DP fin can design will not fail and cause an issue, the same way I have to show that my recovery system design will work as expected.
 
Ez2cDave said:
There are no Rocketry-specific sources of information available, regarding the use of "proper" materials, "proper" 3-D Printer settings, or internal structure of large 3-D printed Fins. So, how does the average Rocketeer, who just plunked down his cash for a 3-D printer, and is a total Newbie, gain this much-needed Rocketry-specific information ?
Click to expand...
To be able to design with any degree of certainty needs a lot of reading on many topics. Materials properties and strength, mechanical engineering (Young's modulus, tensile and compressive strength, natural frequencies and how to change them, other things...), knowledge of the advantages and shortfalls of the different 3D printing processes and what variables affect them, knowledge of destructive testing methodology and access to equipment, reasonable understanding of aerodynamics (total pressure, total temperature, shock waves) and a decent knowledge of bonding methods. I suspect that is a short list.

As more 3D printed parts are flown people get an idea of what is possible and what is not, and then "rules of thumb" and other folk-law are generated, thus allowing the masses to follow that path if they want.

As for the RSO filtering the flights, the responsibility for the flight actually belongs to the flyer. The RSO just catches those that are too keen, inexperienced or reckless. The flyer should know the requirements for the flight before the button is pushed. He can request a "heads up" flight, and also has the option of treating it similar to a complex rocket and pushing to the away pads if it is experimental.
 
Ez2cDave said:
I am not fighting a paradigm shift . . . I think 3-D printing is great, for the most part, BUT . . .

I am objecting to people with minimal experience, inadequateknowledge of proper 3-D printed Fin design, and no public access to the necessary knowledge ( because there isn't any at the present ) , simply printing up Fins with "whatever" material, using "whatever" method, using "whatever" design, slapping them on a large HPR rocket at supersonic speeds, and having them fail out of ignorance. Then, they just "hit reprint" and keep repeating the same errors . . . That is unsafe !

Dave F.
Click to expand...

You object to minimum experience, yet 99.9% of the hobby has no experience with any other materials used in rocketry. Have you done extensive stress tests on plywood fin kits? Doubt it. There a readily available materials that can be printed by off the shelf consumer printers, which are much stronger and more resilient then aircraft ply, are able to be printed to much higher standards etc. this is the major problem with this community. Old timers who know nothing about the topic at hand, but know someone who 3d prints and has an opinion, cry the loudest.
 
I have never used a 3d printer or anything but wanted to read the thread and see what's out there. My background: fast cars, welding/ fabricating metal, I can operate a Mill/Lathe, but I am not a machinest.

YouTube has just about anything now days. 2 other thoughts I had: Solid works for stress analysis on given 3d parts and structures and Finsim.

At some point it may be people with advanced 3d printing skills paving the way, a few options here is over build and up stress until faliure, worst case for safty. Build a split fin rocket with the smaller trailing fin 3d printed and the front fin of conventional material and build practice, so if it fails the rocket could still go upish.

Build a wind tunnel that can go supersonic and test designs, material, technique, AOA, with plenty of thermal image cameras and load cells.

I get it as humans the want to innovate and come up with new ideas.

Back to wood glue and rocketpoxy for me, my thing I want to do is weld up aluminum or stainless steel fin cans.

~John
 
Motocrossman24 said:
You object to minimum experience, yet 99.9% of the hobby has no experience with any other materials used in rocketry. Have you done extensive stress tests on plywood fin kits? Doubt it. There a readily available materials that can be printed by off the shelf consumer printers, which are much stronger and more resilient then aircraft ply, are able to be printed to much higher standards etc. this is the major problem with this community. Old timers who know nothing about the topic at hand, but know someone who 3d prints and has an opinion, cry the loudest.
Click to expand...

OK . . . Put your money where your mouth is .

You, and others like you, in this thread claim to have the knowledge, ability, and expertise in 3-D printing.

Write a "how to" book and become the "Mark Canepa of HPR 3-D Printing" !

Dave F.
 
Last edited:
Ez2cDave said:
OK . . . Put you money where your mouth is .

You, and others like you, in this thread claim to have the knowledge, ability, and expertise in 3-D printing.

Write a "how to" book and become the "Mark Canepa of HPR 3-D Printing" !

Dave F.
Click to expand...
No book needed, people fly them at every launch Iv been to, for the past 3+ years. Yet to see one fail.
 
gldknght said:
I think the point here is, if you don't know whether xxx material will hold up to the stresses of your flight, that material should not be used in your certification flight.

I know that reinforced fins will hold up because others have proved it before me. I know that I needed to add expandable foam to my L3 nose cone based on other's experience. Also, I learned a lot of things on my L1 and L2 projects that will be useful on my L3.

I think that's what Tripoli is saying with this restriction, that more testing is needed and a developed set of guidelines established so the L3 cert flier can show his/her 3DP fin can design will not fail and cause an issue, the same way I have to show that my recovery system design will work as expected.
Click to expand...

I should have had you write the announcement.

Here’s the other part. We are a hobby. We provide certification in order to safeguard the hobby aspect for a wide range of people. People who are able to bring very expensive 3D printers and engineering knowledge to bear are the exception rather than representing most of our members. If we start adopting rules that favor the engineer with the $25,000 printer or $250,000 printer, that makes our hobby less of a hobby and more about who can buy their way to certification. We’re not going to do that. Nothing prevents a person from demonstrating what they can do with their expensive printer, but they have to certify L3 using more traditional skills.
 
TurbulentSphere said:
Made one over here: https://www.rocketryforum.com/threads/printing-tips-for-fins-and-other-structural-components.153658/
Click to expand...

Now if people doing 3D printing will share their results and files for others to use (why reinvent the wheel).

Over the years I've picked up many fins made from G-10, plywood, carbon fiber, aluminum and other materials (my Level-2 rocket used Formica laminate scraps for fins). You could see a few were through the wall by the epoxy on them but either were not done right or velocity exceeded what they had done. Same with 3D printing. I recently even saw a fiberglass 'kit' rocket come apart and on inspection for the cause of the shred (< mach 1) was no epoxy on the root edge of one of the through the wall fins that was found on the ground.

As with any material, experience and the right design are paramount but some of that that experience comes from experimentation, without being able to do that, all rockets would have to be kit rockets and as mentioned, even those can fail.

DSC_0321 TRA Level 2 cert fins (2).jpg
How did my 'countertop' fins work? Fine, but the RSO wrote HEADS UP on my flight card cause he thought they would fail and the LCO failed to announce it was a cert flight to the TRA witness . No problem cause all my L-2 flights were 'cert flights' .
 
Motocrossman24 said:
There a readily available materials that can be printed by off the shelf consumer printers, which are much stronger and more resilient then aircraft ply...
Click to expand...
Plywood is a pretty awesome composite; very strong and able to absorb forces without shattering. I think statements like this need to be supported with data.

This is a very interesting discussion; I think we could come up with some reasonable rules of thumb if we stick to data and don't lose the discussion to histrionics. For example, the tests posted by OverTheTop are a great start.
 
Motocrossman24 said:
You object to minimum experience, yet 99.9% of the hobby has no experience with any other materials used in rocketry. ...
Click to expand...

I wonder what part of the 0.1% would want to see an MOE and a confidence interval attached to that assertion?

I wonder what fraction of that 0.1% has enough math to review an article like this one for journal club?
 
First, let me say, I haven't looked into what can and can't be used for an L3 build. I do know that there are metal fin cans being used for some HPR work, or I'm misinterpreting what I'm seeing out of Mike Fisher's Max Q posts on FB. I'm just tossing this in. So, if I'm dead wrong, please let me know (but don't hammer me for my ignorance).

Upon watching Adam Savage's new show Savage Builds, I'm wondering if this applies for 3D printed metal fins. His titanium Iron Man suit was bullet proof. Admittedly his suit was printed by a team of engineers, and his design was reverse engineered from the actual files used to create the animated Iron Man suit. I know that it cost about a quarter million to make, but a single fin can would be a lot less expensive than that. If a person has the financial means to finance or access to an actual printer, would a 3D printed metal fin can would that still be precluded from a Cert flight?
 
K'Tesh said:
First, let me say, I haven't looked into what can and can't be used for an L3 build. I do know that there are metal fin cans being used for some HPR work, or I'm misinterpreting what I'm seeing out of Mike Fisher's Max Q posts on FB. I'm just tossing this in. So, if I'm dead wrong, please let me know (but don't hammer me for my ignorance).

Upon watching Adam Savage's new show Savage Builds, I'm wondering if this applies for 3D printed metal fins. His titanium Iron Man suit was bullet proof. Admittedly his suit was printed by a team of engineers, and his design was reverse engineered from the actual files used to create the animated Iron Man suit. I know that it cost about a quarter million to make, but a single fin can would be a lot less expensive than that. If a person has the financial means to finance or access to an actual printer, would a 3D printed metal fin can would that still be precluded from a Cert flight?
Click to expand...

Currently yes.
 
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
 
Jose Saura said:
So I think we need to agree on what skills we want to measure and then plan accordingly.
Click to expand...

There is already agreement: can a rocketeer design (or select a design for), simulate the performance of, construct, launch, and safely recover a rocket under the power of an L3 motor? This is demonstrated with the design packet and TAP/L3cc review

3D printing is relatively new technology, and there are folks out there that would have it outright banned for HPR usage because they dont trust it. I'm happy the board has allowed room for its experimentation (just not for certification at the present)

Jose Saura said:
Banning 3D printing is not going to help so I would like to suggest that we instead embrace the new technology.
Click to expand...

As has been stated in thread previously, this is not a total ban on 3D printed fin units. It prohibits their application for a Level 3 certification flight (for the time being). After you have demonstrated that you can construct, fly, and recover a vehicle with Level 3 motors, then you can experiment to your heart's content (In fact the hobby will benefit if you do such experimentation! That way flight data will help illustrate that it is a safe viable method for L3 flights, and the prohibition will one day be relaxed).

Passionate, driven, and intelligent folks often see the certification process as a kind of legalistic hoop jumping. But it is the regulated hoop jumping that allows our hobby to continue relatively freely.
 
Last edited:
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...
Is this the Jose that has the Janus series rockets and flies with TCR sometimes?
 

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