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A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat

bbc.com

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Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat

#71

Post by constantcrying »

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.

Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat

#72

Post by rupellohn »

CarVac wrote: post #2

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.

Full report here: https://assets.publishing.service.gov.uk/media/69297a4e345e3...

The aircraft owner who installed the modified fuel system stated that the 3D-printed induction elbow was purchased in the USA at an airshow, and he understood from the vendor that it was printed from CF-ABS (carbon fibre – acrylonitrile butadiene styrene) filament material, with a glass transition temperature3 of 105°C.

An alternative construction method for the air induction elbow, shown in the Cozy Mk IV plans, is a lamination of four layers of bi-directional glassfibre cloth with epoxy resin. The epoxy resin specified for the laminate has a glass transition temperature of 84°C, after the finished part has been post-cured. The aircraft owner stated that as the glass transition temperature listed for the CF-ABS material was higher than the epoxy resin, he was satisfied the component was fit for use in this application when it was installed.

A review of the design of the laminated induction elbow in the Cozy Mk IV plans showed that it featured a section of thin-walled aluminium tube at the inlet end of the elbow, where the air filter is attached. The aluminium tube provides a degree of temperature-insensitive structural support for the inlet end of the elbow. The 3D-printed induction elbow on G-BYLZ did not include a similar section of aluminium tube at the inlet end.

Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat

#73

Post by gpm »

lazide wrote: post #61
gpm wrote: post #43

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…

The difference is, injection molds are expensive. And the type of people who can afford them tend to cover their ass better - or do slightly less insanely dumb things. 3D printing (especially using filament) allows idiots to enter entirely new areas of endeavor.

I agree, but I note that the 3d printing people are making progress in making really cheap injection molds. I wouldn't count on the difference in cost remaining prohibitive enough that only reasonably serious people can afford it for much longer.

Edit: And I hope the lesson that the safety critical people take away from this is "actual engineering work is needed for airplane components" and not "3d printed parts are scary" because sooner or later they'll run into the same issue with parts made in other ways

Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat

#74

Post by [deleted] »

boothby wrote: post #67
owenversteeg wrote: post #29

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.

What's Tg?

[deleted]

Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat

#75

Post by owenversteeg »

boothby wrote: post #67
owenversteeg wrote: post #29

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.

What's Tg?

Glass-liquid transition temperature, which is approximately where plastics and other materials change from hard and relatively brittle into flexible and rubbery.

As the other comments here noted, it doesn’t exactly mean that the material is safe to use for a rigid part below that temperature, and the transition extends over a range in temperatures, but it does give you a rough idea about the behavior of a material at various temperatures.

Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat

#76

Post by nyeah »

o11c wrote: post #7

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.

I think there's some nuance missing here. "Hot" is a scale, not just a true/false check.

Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat

#77

Post by constantcrying »

o11c wrote: post #7

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.

>The whole point of 3D printing is that the material is moldable when hot but rigid when it cools.

Which means what exactly? Aluminum will go soft under high temperatures as well, yet this part would not have failed if it was made out of aluminum.

The failure is not the material, the failure is someone neglecting the operating conditions or material properties when choosing materials.

This exact part could have also been milled out of some plastic and would have failed the same way. The method to produce that part is only relevant in so far it is open to more people.

Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat

#79

Post by constantcrying »

mdni007 wrote: post #11

3D printing parts is FAA approved?

Some of the most advanced aircraft engines for commercial airliners contain 3D printed parts: https://www.cfmaeroengines.com/leap

The FAA denying approval to parts based on how it was manufactured and not how it performed under testing would be totally ridiculous.

Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat

#80

Post by benatkin »

elicash wrote: post #57
fudged71 wrote: post #27

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.

In what way is this like vibe-coding -- or do you just mean both are bad? According to the report: > The aircraft owner who installed the modified fuel system stated that the 3D-printed induction elbow was purchased in the USA at an airshow, and he understood from the vendor that it was printed from CF-ABS (carbon fibre – acrylonitrile butadiene styrene) filament material, with a glass transition temperature3 of 105°…

The person who coined the term vibe coding is now doing a soylent-like [1] experiment where he only will read content that has been regurgitated by an AI [2], so yes I think it's a fair characterization of "vibe coding".

1: https://nymag.com/intelligencer/2014/10/soylent-creator-hack...

2: https://x.com/karpathy/status/1990577951671509438

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