3D printing an aircraft

The conventional method for wing wiring in an RV is to run a corrugated conduit from wing root to wing tip. In accordance with Van’s recommendations, I’ve enlarged the tooling hole in each rib, and will run 16mm conduit through this hole, secured in place with RTV. Many find that an extra conduit is required, and run it through rib lightening holes. The issue is how to secure this second conduit. The lightening holes in the wing ribs have an arc shaped recess next to them, so I can’t use the Panduit fittings I used in the empennage. I didn’t like Van’s suggestion of drilling a #30 hole and using a cable tie around the conduit. I looked around for a commercial fitting, but couldn’t find anything suitable.

This problem led me to design and 3d print a suitable fitting, custom made for RV-10 wing ribs. The pictured design holds a 20mm conduit, and has two smaller holes for either air lines (e.g. Angle of attack from pitot) or RG-400 cable (for antennae mounted in the fibreglass wing tip). There is a slot for a cable tie, and the fitting nests into the arc around the lightening hole. It is held in place with two pop rivets, and these are positioned so as to cause no interference with a bucking bar held blind inside the wing, since this is how the bottom skin must be riveted. There is a left and right (mirror image) version of the fitting for the respective -L and -R wing ribs.

Common materials used on consumer grade 3d printers are not suitable for this application. PLA has a low glass transition temperature (Tg) of 66 degrees C, so the fittings would easily deform inside a wing parked in central Australia. ABS has a much higher Tg, and is strong enough, but has poor chemical resistance. An AvGas leak working around inside the wing would cause the part to degrade.

The material I’ve used is Nylon – specifically this product. It is very strong but still flexes under load, has a suitable high Tg of 82 degrees C, and very good chemical resistance. It’s harder to use on a consumer grade printer, but once suitable settings are established, the results are excellent and very repeatable. You wouldn’t use this process for anything structural on an aircraft, but I’m sure there will be plenty of other applications for a 3d printed Nylon part before I’m done with this project.

It takes about an hour to print each part, and I need 30 of them. They weigh 4 grams each.

Postscript: The conduit clips work great, I’ve added some pictures of the assembled wing with conduit in place.

  • wing_clip1
    wing_clip1
    Upper side of conduit clip. One rivet hole is recessed so that an LP4-3 rivet has enough depth to set properly
  • wing_clip2
    wing_clip2
    Rib side. The "bump" fits into the recess around the rib lightening hole. Slot on right hand tab is for an optional ...
  • w19c
    w19c
    The Nylon filament
  • w19a
    w19a
    3d printing in Nylon
  • w19b
    w19b
    Part nearly finished in printer
  • w19d
    w19d
    Part complete, ready to pry off the bed
  • w19e
    w19e
    Position of part on bottom side of W-1011L wing rib
  • w19f
    w19f
    Position of part, showing 20mm conduit, AOA air line, and optional cable tie
  • w38a
    w38a
    Right wing gap fairings complete, wiring conduit fitted
  • w38b
    w38b
    Wiring conduit in right wing
  • w40e
    w40e
    Conduit, pitot, AoA lines in left wing
  • w40f
    w40f
    Checking pitot mast arrangement in left wing

 

 

 

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