Mike,
I think you're right . . . During approximately the 6 - 7 second interval in the video.
Dave F.
Mike,
The "drums are beating" and great things are coming in the future !
Dave F.
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Tripoli prohibition on the use of 3D printed fin cans for L3 certification
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Mike,
I think you're right . . . During approximately the 6 - 7 second interval in the video.
Dave F.
Mike,
The "drums are beating" and great things are coming in the future !
Dave F.
If you look in slow motion (1/4x speed) you can see that the entire frame shakes so I think it was more of a camera issue. Screwing the camera on will allow for more accurate flutter analysis.
TurbulentSphere
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The spin wasn't intentional. Each fin is printed individually and then bolted to the motor mount. This can introduce alignment errors (just like traditional construction), but it also allows me to print total fin spans larger than my print bed (unlike single-piece fin cans).
It is amazing how new materials and processes are being developed, opening up many new possibilities. You do get some strange looks and curious questions if you are an early adopter though. When I was flying my printed NC back in 2015 and telling people about some would look at me like I had two heads and should have been in an asylum.
There is at least one person at each launch that comes up with a novel approach. We have to be willing to learn from their success or mistake (just not on their level 3 certification).
How'd you get your rocket to make the "thumbs up" smoke trail? Very impressive..
Absolutely. So many great ideas out there when you look around. Sometimes challenges inspire innovation too. I continue to see great jigs and fixtures that people are able to make due to 3D printing. I tended to not think about that in the past, but 3D printing makes new paths in our techniques.
Dave; Out of curiosity, do you own or have you ever 3d printed anything? If so, was it rocketry related?
beeblebrox
8 C6-0, 12 D11-9, 20 D20-0, 20 E5-0, 3 Cinerocs
Actually your most correct argument there would actually be a PLUS for 3D printed fin cans... They would ensure near perfect alignment, and with thicker profiles being easier to do with tapers to he tip from the root etc. (Nike fin for example) The thru the wall fin can I built from a small model rocket sized one was awesome, so I scaled it up. First test flew great, see above post...Next flight I will push it harder. If it works or fails I will report on it here. As for M-Power or higher, a printed fin can would ensure alignment, If someone is flying M-Motors they aught to have some modeling skills, and especially some common sense. Myidea is to allow for a fiberglass or carbon fiber insert as a thru the wall structural tab. Also the outside of the fins could be covered with a fiberglass, carbon fiber, or even kevlar cloth for strength. The 3d printed core would give you the perfect shape and be lightweight. Now all we need is transparent aluminum...
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mperegrinefalcon
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Yeah, in a different post on here I asked if the fincan is laminated whether or not it would be allowed. You can get a very strong and lightweight component from 3d printing, just when you get into the M motors you very likely need to reinforce the fins if they are 3d printed. I am no expert, this is just my $0.02.
My understanding is this is a ban on using one piece fincans that are 3d printed for L3 certs, not for someone who has already certified as L3. This way you have to actually build the fincan to demonstrate that you know how to build a rocket that can withstand the flight, and not just print yourself one.
No, I don't. I have a long-time Rocketeer friend in Florida who works for a company that employs high-end commercial 3D printing, including printing metals.
He has already 3D printed a fully-operational, all-metal, Colt 1911 .45 ACP pistol which is very impressive. Recently, I have been asking him about getting into 3D printing, myself.
His advise was to "Avoid the "toys" on the market now. Give it a couple more years, if you want to do thinner HPR fins . . . Another price drop is coming and the "next level" equipment will be much more affordable, at that point".
Dave F.
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mazum01
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IMO 3D printed materials need to undergo strength in materials testing in various temperature regimes to really determine usability in L2-L3 applications. With test data, FEM analysis would show one way or another if a 3D printed fin can would work or fail in flight under a given set of flight conditions. Until the larger community can do that, I think the conservative approach is best but the above might suggest a path to allow use.
That would work well for commercially-produced components.
However, the problem comes when employing "self-designed and home-printed" components, because there are no "standards" to compare them to, since each one would be different.
Dave F.
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It's an engineering problem, just like any other that we want to solve on a rocket.
Just to pick some back of the envilope numbers, assume you can get a lift coefficient of 1 out of a fin. Sim to get max velocity and determine the altitude for same. Compute the force potentially produced from the fin assuming that lift coefficient. Run the stagnation temperature computations if it is high velocity. Look up the materials properties under those conditions. Then perform your structural analysis. Design for 50% over minimum required to keep it from breaking to account for all the unknowns.
That's the statics answer. Dynamics is more complex. But if it can't handle the statics, there is no point in considering dynamics.
Gerald
Just to pick some back of the envilope numbers, assume you can get a lift coefficient of 1 out of a fin. Sim to get max velocity and determine the altitude for same. Compute the force potentially produced from the fin assuming that lift coefficient. Run the stagnation temperature computations if it is high velocity. Look up the materials properties under those conditions. Then perform your structural analysis. Design for 50% over minimum required to keep it from breaking to account for all the unknowns.
That's the statics answer. Dynamics is more complex. But if it can't handle the statics, there is no point in considering dynamics.
Gerald
High Desert Rocketry
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I have flown 3D printed two and three piece nose cones made for 4" rockets (both PLA and ABS). The printer was big enough, hence having to glue sections together and flown on up to 'L' impulse motors. None failed in flight (PLA not recommended) but sometimes break upon landing along printing layers. I simply glue back together.
My 4" ABS has peaked out at M1.4 so far, on an M. No problems whatsoever.
3-D printed Nose Cones are not the problem. 3-D printed Fins and Fin Cans are different. They do not benefit from the "hoop strength" and "longitudinal-compression" aspects that benefit Nose Cones. Rather, while being relatively quite thin, they stick out in the air-stream, at up to multi-Mach velocities. They are in a very "harsh environment", compared to Nose Cones, and can be subjected to high loads / forces. Flutter and Thermal heating are also major issues to confront.
Admittedly, you said that 3-D printed Nose Cones can break, even at a slow Descent Rate, upon landing . . . Would not Fins be even more vulnerable to potential failure, particularly in flight ?
Dave F.
If that happens then just press "Print" again. That is one of the advantages of 3D printing.
Keep us informed on progress.
you could say the same for most of our rockets
Having knowledge of structural engineering is a big plus
I think it would be a better idea to correct the problem, rather than to simply duplicate a substandard part. Remember, I am talking about Fins, not Nose Cones.
More specifically, Fins that fail in flight, possibly resulting in a serious accident.
Dave F.
Who says they are substandard? It can also be due to materials and conditions during the print. Some prints warp. Changing the filament or conditions can prevent it next time.
No. It depends entirely on the use philosophy. Either way can be acceptable. Fins or NC is irrelevant. I think you are fighting a paradigm shift.
By "substandard", I mean 3-D printed fins that fail structurally, during flight. Since there areno established "standards" for fin designs and / or re-designs, it can be a "crap-shoot", regarding success or failure. That is a safety concern.
If it is the materials, then ban the offending materials from use in Fins.
"Conditions during the print" . . . There is no way to quantify that, particularly when someone plunks down his money, gets a 3-D printer delivered, and starts churning out Fins for HPR rockets, with no experience, other than being able to run the machine, according to the manual.
Dave F.
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.
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.
Remember too, that having a failure at altitude can be a risk-mitigating strategy, with appropriate recovery system design.
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