3D printing for accessory / non-structural parts

[TaylorMono12]

Assuming that someone from the LAA is on here, I wondered if there is any guidance / policy on using innovative fabrication tools / materials during a build - specifically I'm interested in 3D printing.

I need to fabricate a cradle to contain the batteries for my Leburg ignition set-up and have enjoyed great success using a combination of PeoplePerHour to find developers for the STL / STEP design work, alongside platforms like Fractory.com to do the fabrication.

I am in the process of submitting a mod for the Leburg ignition anyway but I'm curious as to whether - for non-structural parts in my case - whether the LAA have any guidance on things like 3D printing or whether they are generally open to this sort of thing. It seems like the perfect solution for my needs, but there are lots of choices on materials, printing techniques etc and I can't see anything in the allowance materials / strengths datasheets.

Many thanks!

[TRAZZELL]

I'd be interested in where you get to with this question. I've made a few small pieces by 3D printing for my Menestrel (vent/inspection panel in the front turtledeck bulkhead, COM antenna mounts so far). Anything that is basically non-structural should be considered as a possible candidate for 3D printing in my view. Having said that, I am going to replace the PLA parts with a tougher material such as PETG which is more resilient and has a higher temperature capability (during the pandemic, I made 50 head-pieces for medical face guards out of PETG which needed to be sterilised at higher temperatures that PLA would be capable of).

Tony Razzell

[TaylorMono12]

I'm currently awaiting fabrication of a PETG harness for 2 batteries for the Leburg - these will be mounted in the recess behind my headrest, so already quick secure but the harness should prevent them moving about in lumpy air. It's exactly the sort of use case for this - although there are lots of variables I'm having to get my headaround like in-fill, materials etc so learning as I go.

I don't have CAD experience myself so I've been doing the drawings by hand, or in PDF, then getting someone on PeoplePerHour to correctly design them in the right file format. Then using resources like MakerVerse or Fractory to quote for the work.

It's really amazing how you can pretty much get anything made in any material in a few days, all from a sketch.

[Penguin]

First of all I don't know much about Monos or VW conversions.
It is very easy to think something is not "structural" but if you were hit a sharp gust while flying or to stop (very) suddenly on landing it is important that heavy items like battery are sufficiently restrained to avoid them breaking loose and bouncing around, including bouncing into you.
I would discuss your plans with your inspector as early as possible. You never know what is experience is and what he might know. It is reasonably straight forward to carry out some rudimentary loads analysis assuming 9g forwards/backwards, 6g up/down and 3g side to side (as a first pass). If your chosen material can withstand those loads you may have a chance of creating an acceptable solution. A harness is for restraining you, not other things that it might pass over. A battery box really needs to be bolted down to something solid.

[TRAZZELL]

I agree that a simple stress assessment would be a good idea. There is information available online on the strength of PETG and other 3D print filament materials. A quick google search yielded this paper for example: https://www.sciencedirect.com/science/a ... 2424000355

The 3D printing parameters appear to be important - basically go for high density, higher print temperatures and slower print speeds to get the best properties which intuitively make sense.

Tony

[TaylorMono12]

Totally agree on all the above. My question really was - given that 3D Printing has been around for the best part of 15 years - surely there must exist some structural analysis in the GA world and I assume that the LAA must have pondered the question of 'what to do about it' prior, that's all. I would imagine this topic has come up hundreds, if not thousands of times already in the homebuilt world globally.

It would be very interesting to see if any guidance already exists on this topic!

[Penguin]

Talk to your inspector!
You are assuming a lot - because of the variables with 3D printing it is difficult to "do some stress analysis" without knowing exactly what material will be printed at what density and the design of the part. Some basic features, such as sharp edged flanges for bolted holes, can have a significant impact on the loads a part can withstand. LAA Eng will generally react to a modification proposal, have you searched the list of approved mods?