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

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

#221

Post by Doxin » Mon, Dec 08, 2025, 1:01 PM UTC

michaelt wrote: post #208

ahepp wrote: post #103

Earlier quoted context omitted.

Do we know whether the part was made out of spec, or whether the spec specified inappropriate materials?

It sounds like it was something like PLA when it was supposed to be ABS. According to https://assets.publishing.service.gov.uk/media/69297a4e345e3... > The aircraft owner [...] understood from the vendor that it was printed from CF-ABS (carbon fibre – acrylonitrile butadiene styrene) filament material, with a glass transition temperature of 105°C [...] he was satisfied the component was fit for use in this applicatio…

You'd be very hard pressed to confuse PLA with carbon fiber reinforced ABS. The latter has a definite surface texture that's hard to get confused with that of PLA.

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

#222

Post by Doxin » Mon, Dec 08, 2025, 1:04 PM UTC

potato3732842 wrote: post #176

averynicepen wrote: post #105

Earlier quoted context omitted.

3D printing is to mechanical engineering what vibe coding is to computer science. With the rise of accessible 3D printers that can print engineering materials, there are a lot of people who try to create functional parts without any engineering background. Loading conditions, material properties, failure modes, and fatigue cycling are all important but invisible engineering steps that must be taken for a part to func…

You don't need to be able to mathematically jerk the equation off to understand why increasing material at the perimeter adds more strength than the center (within reason and in typical cases) or why you probably shouldn't use something that melts around 200deg in an engine bay.

Note that the actual material used has a glass transition temperature around 50 degrees, not 200. If the part was actually made from ABS-CF (as the pilot thought it was) it'd stand a decent chance of surviving for a long time given that it gets a lot of air cooling.

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

#223

Post by Ancapistani » Mon, Dec 08, 2025, 5:05 PM UTC

bombela wrote: post #219

2muchcoffeeman wrote: post #214

Earlier quoted context omitted.

I’m not necessarily saying it can’t be done. But these are plastics that fail under heat. I’d test part for non critical applications and I’m just a nobody amateur. These guys are messing with planes and don’t test enough? Is there an explanation these people aren’t just incompetent?

> But these are plastics that fail under heat. All materials ultimately succomb when exposed long enough at some high enough temperature. What is the temperature range to match here?

> All materials ultimately succomb when exposed long enough at some high enough temperature.

I'm not a material scientist, but I don't believe that to be true. Metals don't to my knowledge; they suffer oxidation, which is allayed by the presence of oil.

If you mean plastics in particular, then PEEK would be ideal to my knowledge - it's suitable for immersion in gasoline and similar solvents, and I've used it in the past for a fuel pump mounting bracket that sits inside the fuel tank of a (gasoline) vehicle. I checked it after a year and it doesn't seem to be any worse for wear.

It's just a huge pain to print!

> What is the temperature range to match here?

I'm not sure, and likely couldn't be sure without a fair amount of research. If I had to print this for a plane, I'd want to do that and measure temperature in use and under high load and destructively test several drafts to ensure performance.

From what I've seen in this instance though, the failed part showed a Tg (glass transition temperature) of 55ºC - basically exactly that of PLA-CF. The pilot believed it was ABS-CF, which has a Tg of ~100ºC. If we assume that 100ºC was at least higher than the expected operating temperature, PEEK (Tg: 143ºC) would have given a ~50% safety margin.