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

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wsume99

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The same logic applies to flying pyramids, spools, and other oddroc designs, but I have heard zero complaints from people that those are specifically disallowed for cert flights.

I really don't think this restriction is that unreasonable. Once you're certified, you can do whatever you want, but L3 cert projects need to be easily evaluated by TAP members.
No, that logic doesn't apply. The examples you listed don't fit the 3 or 4FNC rocket type. The major difference between a 3D printed 3FNC and a conventionally built one is the method of construction. They are the same design when it comes to loading and stability. This is not true for the examples you gave.

I agree with your point that TAPs need to be able to assess cert projects. But if TAPs are certifying 3D printed fin cans on L1 & L2 projects I don't think that L3 requires any additional special considerations for evaluation of the fin can. You're still evaluating the same basic thing, will the design presented withstand flight loads.

I still maintain that the certification process is demonstrating that the applicant can build and fly a 3 or 4FNC type (clarified because of the above point) amateur model rocket safely. The method of construction doesn't change this.
 
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Ramjet

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I have been 3D printing for several years with multiple materials. No WAY am I 3d Printing a level 3 part. I have seen how easily 3D printed parts fail in non rocketry items and the forces on a L3 Rocket an MUCH Higher. I have not yet printed in Carbon Fiber, So I may revisit this issue at a later time.
 

Maxwelljets

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I agree with your point that TAPs need to be able to assess cert projects. But if TAPs are certifying 3D printed fin cans on L1 & L2 projects I don't think that L3 requires any additional special considerations for evaluation of the fin can. You're still evaluating the same basic thing, will the design presented withstand flight loads.
The cert procedures for L3 are far more involved than for L1 and L2. All that's required for those 2 are a successful flight. You can't just show up and fly an L3 project. The TAPs are involved from close to the very beginning of the process. You need to submit documentation and other paperwork showing the design and construction details of your particular rocket, so that the TAPs can verify that they think the flight will be successful.

And yes, the logic very much applies. You gave your opinion that if one is allowed to fly with a printed fin can after L3 certification, then one should also be able to fly with a printed fin can for the L3 certification flight. Exactly the same logic as saying that since you can fly an L3 spool or pyramid after certification, you should be able to certify on a spool or pyramid.

Additionally, commercially manufactured fin cans such as the ones from Max-Q Aerospace are banned for L3 certifications, even though they're allowed for regular L3 flights, and there's no uproar about that. You also can't stage or cluster for a cert flight. The point I'm making is that there are many things you're allowed to do after you're certified that you can't for the flight itself. Cert flights are different than normal flights.

Again, this rule really isn't that unreasonable. Once you've gone through the process, you can do whatever you want, be it spools, pyramids, bolt-on fin cans, or 3d printed fins.
 
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wsume99

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Cert flights are different than normal flights.
Exactly. And that's why spools, pyramids, and oddrocs are banned because it has been determined that 3 and 4FNC type rockets are the only valid rocket types for certification. Commercially manufactured fin cans are banned because then you are not building a part of your rocket which has been determined to be critical to demonstrating sufficient knowledge and building skills. If you print your own fin can then you have built it and demonstrated sufficient design knowledge. The issue is with the method of building/assembly. Are other forms of traditional assembly for 3/4FNC rockets specifically limited or banned?
 

OverTheTop

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I have been 3D printing for several years with multiple materials. No WAY am I 3d Printing a level 3 part.
Chicken :p.

If designed properly there is nothing wrong with printed parts. They do need to be designed appropriately. Here is a design you might want to look at (two-stage, O3400-M2020):
https://forum.ausrocketry.com/viewtopic.php?f=6&t=5019
Feel free to use any of the ideas :).

I also used SLA printed fins successfully on my vertical trajectory system. I have no hesitation using 3D printed parts where they are appropriate.
 

Jose Saura

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I have been 3D printing for several years with multiple materials. No WAY am I 3d Printing a level 3 part. I have seen how easily 3D printed parts fail in non rocketry items and the forces on a L3 Rocket an MUCH Higher. I have not yet printed in Carbon Fiber, So I may revisit this issue at a later time.
The problem with anecdotal references is that there is no way to reproduce results and understand the context. I have also seen things built with wood, fiber glass and metals fail.

I think the suggestion others proposed on this discussion thread about documenting results (successes and failures) in more detail is important and will allow us to make progress so I plan to do so in the months ahead.

I do recommend you try Nylon and Nylon with Carbon Fiber and if your parts are still failing, it would be great if you could post your results so people can learn and provide feedback.
 

jbsommerfeldt

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The original post was to simply state the BOD will not allow 3d printed fin cans for certifying level 3 flights. It is not banning pushing the limits of new building techniques on level 3 rockets. Get your level 3 with any plethora of capable standard parts. K.I.S.S. After you get your level 3 do what ever you want. Keep in mind the club launch must allow it, level 3 cert or not and the RSO must sign off on it.

I cant wait until my grandson goes for his level 4 and the requirement for a minimum 5 minutes of low earth orbit are mandatory! That’s gonna be cool.
 

hball55

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Speaking of 3D printed fin cans not being strong enough, I can attest to that. I used a 3D printed fin can that I purchased from the guy who first started printing the electronics sleds that Missile Works sells, on my 54mm min dia rocket and flew it on an I65 motor. The rocket corkscrewed after it left the rail and arced over for a very unsatifying flight. When I recovered the rocket, I was amazed to see that the fins had melted into the shape of the propellor of a boat motor. Two fins curved in one direction and the third fin curved in the opposite direction.
 

Buckeye

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Speaking of 3D printed fin cans not being strong enough, I can attest to that. I used a 3D printed fin can that I purchased from the guy who first started printing the electronics sleds that Missile Works sells, on my 54mm min dia rocket and flew it on an I65 motor. The rocket corkscrewed after it left the rail and arced over for a very unsatifying flight. When I recovered the rocket, I was amazed to see that the fins had melted into the shape of the propellor of a boat motor. Two fins curved in one direction and the third fin curved in the opposite direction.
Uh-oh. Is it one of these?:


I was raving about these cans, but I have not flown mine yet, and I did not consider melting as a possible failure mode. I was planning on min dia with long burn motors (like your I65 experience), now I have 2nd thoughts.

Edit: better picture
 

hball55

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Uh-oh. Is it one of these?:


I was raving about these cans, but I have not flown mine yet, and I did not consider melting as a possible failure mode. I was planning on min dia with long burn motors (like your I65 experience), now I have 2nd thoughts.

Edit: better picture
Looks much like the same material, lol. One recommendation, put a bit of distance between your rocket and the blast plate. I think the blast back off the plate contributed to the melting. I don’t know what the optimal distance would be, I think my motor was only about 6” from the blast plate, so try raising your rocket another foot.
 

cwbullet

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I have been 3D printing for several years with multiple materials. No WAY am I 3d Printing a level 3 part. I
I think 3D printed nose cone with the right infill pattern or an AV sled is fine. PC Blend or advanced fibers made into fin cans might be ok, but I am not doing it with a level 3 motor. The bottom line is that this stuff should probably not be used for minimum diameter or anything high thrust. I have seen it done successfully. I am just not doing it.
 

Dustin Lobner

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I'm slowly working up the power ladder. Biggest I've flown with a 3D printed monolithic fin can/motor mount is a J450 (my avatar pic actually). Zero issues there. Planning on flying a K535 with that sometime this spring. After that, the next flight is an L1000 or K455NW.

I believe that an M is doable. What I do is print the bottom inch or so at 10 solid layers and 100% infill, give it a solid piece of plastic to push against. Maybe more like 2 or 3" for an M, lol. I've also done tensile testing to know what the best print temperature is. Also, taper the fins root to tip...mine start 10mm wide base, usually 5mm wide tip, and then like a 15mm radius fillet on the fin root...they're strong.
 

jqavins

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Alright, I'm jumping in late and have not read all the posts. That said:
If the board were to accept self printed fin cans for all three levels (remember that they are already accepted for L1 and L2) it’s possible that a person could certify all three levels without ever knowing how to use glue a fin on straight. Is that acceptable?
Yes, I think it is. After all, one can already certify L3 without ever knowing how to design a rocket with a slide rule, like we did it in the old days. OK, that's a somewhat facetious comparison. One also doesn't need to know how to do a fiberglass lay-up, or design and solder a dual deploy altimeter, or a lot of other things.

The most important thing about certification, I should think, is demonstrating knowledge of safety principles, including the design and fabrication aspects thereof. If a 3D printed fin can can be safely used, and the flyer can demonstrate knowledge of how and why his/her fin can is safe, then I don't see a problem. If that flyer, having been certified, decides later to make a great big rocket with fins more traditionally glued on, the certification means that we trust the flyer to make safe decisions, like getting help gluing the fins on straight if s/he has never learned how before.
 

Steve Shannon

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Just to close the loop, at the November 2020 board meeting, the Tripoli BoD voted to leave it up to a person’s TAPs whether a self made 3D printed fin can would be acceptable for an L3 certification flight. New wording appears in the L3 certification procedure.
Alright, I'm jumping in late and have not read all the posts. That said:

Yes, I think it is. After all, one can already certify L3 without ever knowing how to design a rocket with a slide rule, like we did it in the old days. OK, that's a somewhat facetious comparison. One also doesn't need to know how to do a fiberglass lay-up, or design and solder a dual deploy altimeter, or a lot of other things.

The most important thing about certification, I should think, is demonstrating knowledge of safety principles, including the design and fabrication aspects thereof. If a 3D printed fin can can be safely used, and the flyer can demonstrate knowledge of how and why his/her fin can is safe, then I don't see a problem. If that flyer, having been certified, decides later to make a great big rocket with fins more traditionally glued on, the certification means that we trust the flyer to make safe decisions, like getting help gluing the fins on straight if s/he has never learned how before.
I agree. In November the BoD changed the rule to allow 3D printed fin cans to be made by the flyer and used in their L3 certification flight with prior TAP approval.
 

Johnly

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I agree. In November the BoD changed the rule to allow 3D printed fin cans to be made by the flyer and used in their L3 certification flight with prior TAP approval.
I've seen large L3 capable rockets fly without issue on 3d printed fin cans and others.... well not so good. Major design factors for 3D printed structures are infill, print direction, and material; hopefully there is guidance being provided and successes and failures tracked. All in all, I''d wager that recovery system failures will remain the majority reason for unsucessful L3 certification flights.
 

EeebeeE

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Does this prohibit just one-piece 3D printed fin cans, or does it also include 3D printed fins and components? I'm working on designing a 3D printed level 3 project, but the fins are individual pieces that are bolted to an internal structure. I haven't finished the design yet, but the construction will be similar to this (but with a different motor mount): https://www.thingiverse.com/thing:3164819. I have a few more iterations before the L3 rocket (a K-class and L-class envelope expansion), but should I start looking at other methods if it isn't allowed?
You should check with your TAP, who can approach the L3 committee.
 

cwbullet

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I agree. In November the BoD changed the rule to allow 3D printed fin cans to be made by the flyer and used in their L3 certification flight with prior TAP approval.
That is good news. I would think the mentorship by someone with experience is key.
 

Monoxide

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I think leaving it up to the TAPs is a good move. I've done lots of 3D printing in everything from rockets to RC planes. It is definitely an art and a science, and takes some experience to recognize a strong yet lightweight design.

It's inappropriate to exclude 3D printing parts and not exclude CNC milled parts. For example, what's the different between a person 3D printing someone elses g-code file and milling someone elses g-code file? Both are pretty much set-up, press go.

But I think we're missing the point. Anyone can overbuild a rocket and say yes it's going to be safe. But it takes real talent to build a rocket with a margin of safety of say 1.3 or 1.5. Proving a rockets safety should be the same regardless of construction/material. Load testing, engineering data, published specs... Whatever the proof is, should not be based on the material, but the expected performance of the rocket. That's how you prove safety. That's what L3 should be testing.

I think it's in complete right of anyone checking out an L3 with questions on the integrity of the rocket to request proof supporting construction materials/techniques. We're never too smart to learn something new ourselves.
 

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