I think this needs to be added to the urban dictionary "Cozy pilots are the aviation equivalent of people who run Arch Linux as their daily driver"

Figured it was experimental; no A&P who cared about his future would install a 3D printed part on a certified aircraft.

Actually, I think all of the jet engine manufacturers these days are using 3d printers for some of their parts? Although you usually find the press releases talking about this using the term "additive manufacturing" instead. See, e.g., this press release from 2018 about a notable jet engine manufacturer using 3d printing: https://www.geaerospace.com/news/articles/manufacturing/manu...

(Although note that these are not using plastic parts, to be clear.)

Yes, implicit was that it was an uncertified part 3D-printed by "someone" who sold it at an airshow. Obviously a certified part from the manufacturer is a different story.

The 3D printing isn't the actual problem, as you note.

It's not the "3D printed" aspect of the part that's driving the failure, it's that it's made out of thermoplastic. An injection molded part in this situation[1] would likely have failed in the same way.

[1] It's not clear what the source of the heat was or where this was in the motor enclosure. But yeah, one needs to be careful with structural plastic near running engines!

Thermoplastic is the problem here. There are plenty of thermoset and other kinds of plastics that handle heat well and don’t soften with heat in normal ranges. 3d printed thermoplastics typically need to be liquid at <300 C so the glass transition usually is closer to 200 or even less. Definitely not suitable for the engine bay.

Manufacturers who use 3D printing use specialized 3D printers, not the same thing that hobbyists use.

They also handle all of the testing of parts to ensure they meet the design spec and they have the equipment to validate each printed part to ensure it doesn't have any major defects.

You can see the layer lines in the part. WTF? I don’t build aircraft parts. But I sure as hell wont use thermoplastics in this situation. I don’t even 3D print parts for mildly hot environments where failure is just annoyance.

Whoever built this should be charged.

> Whoever built this should be charged.

This is an uncertified experimental aircraft. At least in the US, it is up to the operator of an experimental to ensure that parts are fit for purpose.

I've printed and used intake manifolds for (automotive) engines in the past, without issue. Obviously that's not the same stakes as an aircraft, but I don't see why it wouldn't be possible to do safely.

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.

Not that I can think of, honestly. I'd be extremely hesitant to use a part I printed on an aircraft. If I had to, I'd make very sure to test multiple copies to destruction.

I think spacex uses it too, that's probably key to their engine becoming smaller and smaller over time.

Getting it certified for flight is insanely difficult because one of the challenges of AM parts reproducibility.

Loads of commercial aircraft and jet engine parts are manufactured using additive manufacturing, or ”3D printing”

Yes… but more often something like laser-sintered metal printing, which is not going to melt when hot.

Yep, and it works even in the SpaceX Raptor engine.

A 3d printed Inconel part would be fine. 3d printed plastic is something else entirely...

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 application when it was installed.

> [...] Two samples from the air induction elbow were subjected to testing, [...] The measured glass transition temperature for the first sample was 52.8°C, and 54.0°C for the second sample.

I've known 3D printing folks who run off a throwaway prototype in a cheap, easy-to-print material to check for fit before printing in more difficult, expensive materials. Easy to imagine a careless manufacturer getting the PLA prototype mixed in with the ABS production parts, and selling it by mistake.

Of course, the aviation industry usually steers clear of careless manufactures....

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.

That's... absurd. ABS is a terrible choice for anything in an engine bay - ABS breaks down over time when in contact with oils.

I've used PA6-CF for similar purposes in the past. Obviously not for aircraft, though.

Even in ABS I would not use something 3D printed on a consumer machine as a critical part of an airplane.

I don't know if it is the same in the UK as it is in the US, but the appeal of experimental aviation (every Cozy is experimental) is that there are no specs or requirements around parts like this.

If you want to slap 15 weed-wacker engines to a wing you made from styrofoam and call it an airplane, the FAA will not stop you.

I'm oversimplifying, a bit, but less than non-pilots might think.

In other words, the engine maker probably has some thoughts about how that piece should be made, but the FAA would have no problem with you installing it on an experimental.

My understanding of the UK CAA is that it isn’t as liberal as the US FAA when it comes to amateur-built experimental aircraft airworthiness. I would still be surprised if a 3d-printed intake manifold on a homebuilt passed an airworthiness inspection in the US without a number of detailed questions being answered to the satisfaction of the airworthiness representative.

The spec is fiberglass, which has better thermal resistance.

But not that much better compared the better filaments out there. Fair chance it was printed out of PLA, ABS or PETG, by the shade of the part it looks like it was CF loaded filament.

A better choice would have been PEEK. But even then, I would have done a lot of on-the-ground testing before trusting my life to a part from the printer.

100% -- the original design for the Cozy is from the early 90s, before 3D printing became popular, and this part seems like a good candidate for 3D printing. It just seems like the maker chose the wrong materials and didn't test it adequately.

It's a candidate, but it is definitely not a run race, temps under the engine covers of a plane can get surprisingly high (surprising because you'd think you have plenty of airflow half a meter behind a pocket hurricane). I'm not sure if high temp filaments would be the solution here, but they'd be better candidates. It would need some very thorough testing before trusting your life (or in this case: someone else's) to that kind of solution.

My guess, given the sheen that looks like CF would be PA-CF, which is the most appropriate and common filament with CF.

And PA-CF is usually pretty good with temps, I have used it for parts on engines before with good results, but not in safety critical scenarios.

There’s a massive difference between the thermal properties of the materials you listed.

Yes, that's why I listed them. And even then: none of those first three are (safely) usable for this application. PEEK or ULTEM or something better than that.

I absolutely agree. At the same time, I’m just flabbergasted that someone really thought they’d pass off PLA crap for such a purpose, it literally loses shape in sunlight. PETG isn’t going to cut it and I wouldn’t want to be on a plane with PETG in a heat-sensitive part, but that would still have been less ridiculous given that a) it’s significantly better than PLA in this regard, and b) unlike PEI and PEEK, it can be printed with ease on just about any FDM.

Whoever sold that part deserves to be sued. I'm not from the 'sue happy' department but this was extremely irresponsible and unless the swap for PLA was accidental (which can easily be proven, they must have sold more than just one of these). At a minimum they should recall each and every one of these they have made and on top of that they should review all of the other parts that person has made for similar issues.