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.
A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat
41–50 of 223 posts
Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat
#42The 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.
Plastics under load have a lower Tg.
Isn't Tg a poorly defined metric? It seems like thermoplastics will lose their strength as temperature goes up and there's no abrupt transition where there's a near step-change in behavior
Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat
#43I 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.
Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat
#44Earlier quoted context omitted.
CF-ABS > 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 wa…
> The epoxy resin specified for the laminate has a glass transition temperature of 84°C This seems very low for the kinds of epoxy I've used. I wonder if the manufacturer specs are highly conservative? Or maybe the material has a shortened lifespan with even moderate temperatures? I was thinking about the ABS in the article and wondering if I would have made the same mistake. Close to every car manufactured today has…
There are some incredibly low Tg epoxies out there, such as West Systems 105 where "TG onset" is 54°C and the heat deflection temperature is even lower.
Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat
#45I 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:
Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat
#46The 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.
Plastics under load have a lower Tg.
Tg changes? Or do you mean they deflect sooner under more load?
Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat
#47Earlier quoted context omitted.
Plastics under load have a lower Tg.
Isn't Tg a poorly defined metric? It seems like thermoplastics will lose their strength as temperature goes up and there's no abrupt transition where there's a near step-change in behavior
It kind of is, a better metric is HDT (Heat Deflection Temperature), and it is based on curve usually load over temp.
Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat
#48i'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.
Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat
#49It'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.
Re: A Cozy Mk IV light aircraft crashed after 3D-printed part was weakened by heat
#50Wow. It's called "thermoplastic" for a reason.