alt Hacker NewsA Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat
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This is the mechanical equivalent of vibe coding. 3D printing itself isn't exactly to blame but the negligence of the company that created and sold this part and omitted it's use from an inspection.
Just because a part has the shape of an engineered part does not make it compatible, strong, safe, and fit for purpose. This part could have likely been fine if it used a different material such as Ultem.
Taken at face value, this is engineering negligence. I've done industrial design with plastics and 3D printed parts. Regardless of the forming techniques, with plastics you still need to consider properties like minimum melting temperatures, tensile stress, and so forth. Then you must test that rigorously. This is all standard procedure. That information is in the data sheet for the material.
I did a quick search and found that many plastics are governed by ISO 11357 test standard [1]. Some of the plastics I have worked with used this standard.
A spec sheet for that material is here [2].
[1]: https://www.iso.org/standard/83904.html
[2]: https://um-support-files.ultimaker.com/materials/1.75mm/tds/...
The part was claimed to be ABS-CF. UK AAIB tested the part and found it to have a Tg of approximately 53C. The Tg of ABS is far higher, around 100C. I suspect that the part may have been accidentally printed with PLA-CF (which has a Tg of approximately 55C.)
The original part was fiberglass/epoxy with the epoxy having a Tg of 84C.
I showed this to a pilot friend of mine out of curiosity, he noted that this type of aircraft is usually kit built / home built. So the fact a part of it was 3D printed was not a total shock.
Edit:
Actual report: https://aviation-safety.net/wikibase/487013
Material was CF-ABS
I wonder if just including the aluminum tube that was effectively acting as a heat break would have been enough...
Really it seems like a problem of not understanding the environment, and testing (with margins) your replacement in it... 3D printing seems nearly entirely unrelated apart from enabling people to make parts.
An injection molded part, for a close more traditional analogue, would presumably have failed the same way here.
Also the glass transition temperature reported in the report is suspiciously low for ABS and the only source on the material is the owner saying the person they bought it from said... I wonder if it was just outright made out of the wrong material by accident.
Not to be a 3d print snob but....
Aside from the failure it looks like it wasn't the best print to start with. Lots of rashing from support and curling at the edges. You can see on the flats where the support was and the outer curve of the elbow looks like it likely wasn't airtight. Appears to me to be printed with the inlet facing upwards.
Better support planning, settings and possibly orientation may have helped.
Other commenters are saying it was likely PLA-CF, which I totally agree with based on the testing, but I can't help but think there is no possible way the person printing this item did not know that. I doubt the print would have come off as good as it did when using ABS-CF settings on PLA-CF.
Big chain of poor choices.
Is this a Part 103 Ultralight?
Also it's insane that they used a bolted joint with plastics on a critical place, the plastic will creep under the clamp load and will lose clamp force.
Thankfully minor injuries.
A thermoplastic in an engine cowling is insane. It’s crazy that this was being sold the supplier should have known better, as should the buyer. 3D printing can be used to make a fiberglass or carbon fiber mold which is already a lot of the work of making the part.
It would be interesting to know what filament was used, in theory some high temp filament could be suitable but I would be nervous putting those on a car let alone a plane.
Edit: https://assets.publishing.service.gov.uk/media/69297a4e345e3...
The actual report includes the important details, ABS-CF which they thought was safe because they underestimated the glass transition temperature of epoxy fiberglass.
Why is the 3d-printed part highlighted; upon first reading this looks like the part softened; it didn't separate on FDM boundaries. Wouldn't a similar thing have happened if it were formed in a different way, but of the same materials?
The actual report[1] holds the answer to the question you’re asking.
CF-ABS (or so claimed)
[1] https://www.gov.uk/aaib-reports/aaib-investigation-to-cozy-m...
I wonder what material it was printed with.
edit: It was ABS-CF, which shouldn't be used under stress long-term in higher temperatures than maybe 65-70°C, or lower depending on the blend.
I'm massively paranoid that some cable clips I printed that will sit on a circuit board will perish in the heat. Meanwhile, some idiot couldn't care less about thermal stability for flight hardware!
Belite, a company that folded (and just renamed themselves) after a certain number of crashes of their experimental ultralights, sold my dad a plane where the AOA sensor was malfunctioning, the propeller hit the ground if there was someone in the plane, and one wing side was longer than the other. By a visible amount. My dad broke a set of propellers and they sent him a new set with 3" cut off each blade. i have those in my shed.
I'm no aerospace engineer or anything, but that plane shouldn't have been able to stay in the air.
and, lo, it didn't, the motorcycle engine used as the prime mover sputtered out at 200' AGL and since it's not a glider (and i don't even think it can glide), it crashed straight into the ground.
Fly an ultralight if you want, just be aware that people will think very poorly of you.
I just watched a fun video of a guy bringing a 1978 Datsun 280Z up to date. He kept the existing engine but upgraded it with modern electronic ignition and computer control. As part of all that, he fabricated various parts in plastic by 3D printing, but then had the final versions made elsewhere in metal -- some by a CNC shop you send CAD files to, and one by a manual machinist in Switzerland with his own Youtube channel. The latter has to be case hardened, which the machinist did.
The 3D printed plastic parts were very useful to prove out the parts' shapes.
https://www.youtube.com/watch?v=jZ38C-M3tyk -- engine upgrade
https://www.youtube.com/watch?v=D2bxsEyYdo0 -- My Mechanics making the part
At a glance, that looks like worse than merely the negligence of using a new technology.
The whole point of 3D printing is that the material is moldable when hot but rigid when it cools. And people really should be aware that engines get hot.
Hah! I've actually 3D printed a part of an intake before. Just as a prototype, to allow me to get a Keihin carb on a motorcycle that had a CV carb.
Printed it on an SLA machine though! I was concerned enough about chemical attack even then, even though it was a temporary part. Never really thought about doing it in filament.
Are those class 8 bolts holding a plastic (PLA? PETG?) part in place? I guess the original part would have been some sort of metal?
It's a light aircraft, the owner probably built it and is allowed to fix it. So it's probably not a company that printed the part.
The person that installed should have thought more carefully about it. But the person that printed it and sold it should face some legal repercussions. Totally irresponsible what they did.
i'm confused: if they were on final and lost power, why not just glide to the runway??
edit: nvm, i found my answer in the actual report.
They included everything but the 3D printed material. If it was PLA, no surprise (and no excuse). Even ABS might not stand up to the temperatures at that location. I hate it when a news report tells you everything except details that might make a difference going forward.
correction to the title: the plane crashed because the owner is a moron, not because he bought a 3d printed part but because he failed to ensure his provider is trustworthy and instead used a fly-by-night nobody to fit a machine that can kill him at any moment.
Absurd what people will do to save a buck.
Hardware engineering is hard. Especially for any safety critical component.
In this case engineering was done by someone, who either did not understand the material he was working with, or the operating conditions in which that part was deployed.
Obviously no testing or any kind of proper engineering was done to create requirements validate them and verify them.
Being able to design a 3D model and print it does not mean you are done with engineering. It is just one step in a very long chain, which is needed to produce devices which stand up to their use.
Wow. It's called "thermoplastic" for a reason.
And this is why (at least for the US) aviation parts have such an onerous paperwork overhead, why a seemingly cheap part like a $.50 bolt balloons to much greater. Granted this aircraft was a UK-equivalent to "experimental" in the US, where you can pretty much do anything to it, I'm of the opinion that doesn't excuse maintenance and adding fly-by-night parts that borders on negligence. Stick to a minimum standard, if not just out of shame of something that could happen.
The part was a "plastic air induction elbow", i.e. this kind of thing:
https://duckduckgo.com/?q=plastic+air+induction+elbow&ia=ima...
so, if you were thinking "who would use a 3D-printed part", remember that it may otherwise also have been made with some liquid material, but using a mold, and perhaps two parts using a mold that are joined with re-heating etc. - and now it no longer sounds so outlandish.
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I hope 3-D printing becomes obsolete when robots can achieve the same efficiency with using the standard construction materials. That should take away all benefits of 3-D printing over regular builds.
It's important to note the plane is a Cozy Mk IV, which is an experimental light aircraft that is built at home out of foam and fiberglass by following instructions you get online. The design is very good, and hundreds have been flown over the last ~35 years, but Cozy pilots are the aviation equivalent of people who run Arch Linux as their daily driver; many of them are tweaking their aircraft with some frequency.
This isn't a case of an established aircraft manufacturer cutting corners on a part; it's probably some small maker who made this part out of the wrong materials. It's a little shocking that neither the maker nor the buyer of this part thought to either stick it in an oven or run it with the engine on the ground to guarantee it could hold up to the expected intake air temps. I'm glad the pilot made it out with only mild injuries.
edit: here's a fun video from a Cozy pilot in case you're curious about the plane and the people who fly them: https://www.youtube.com/watch?v=Ipqmb09wbSQ