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




Right wing match drilling, tear down, dimpling [18.0 hours]

I match drilled the right wing, tore everything down, dimpled as required and scuffed all parts. There was a lot of work involved in this, and at the end of it I wound up with a pile of parts which looked much the same as I started with. No point in any pictures, it all looks the same as before.

  • Match drill top and bottom skins, gap fairings: 6 hours
  • Countersink fairing plate nuts, top skin wing walk area: 2.5 hours
  • Disassemble, de-burr, dimple everything except skins: 9.5 hours

Now for the same with the left wing.

Assemble right wing skins, gap fairings for match drilling [4.5 hours]

I de-burred the right wing gap fairings and skins, and cleco’d everything together, using just about every cleco I own. The skins are over-cleco’d in places, but since I’m deviating from the normal build order I wanted to make sure of the alignment for match drilling. I needn’t have bothered, the hole match-up was perfect. It’s going to take some time to match drill everything.

  • w18b
    Right wing, top skin fitted
  • w18c
    Back on stand with top skin fitted
  • w18d
    Inboard bottom skin and gap fairings cleco'd on
  • w18e
    Both bottom skins cleco'd in place


Rear spars, trim, and build order decisions [15.0 hours]

I completed match drilling of the rear spars and tore both wings down to de-burr the affected parts, winding up with a pile of parts to be primed.

I’ve decided to deviate from the documented build order. The fuel tanks, which I’ve outsourced, will be completed and back here in a few weeks time. There is a bit of main spar work associated with the outboard leading edge tanks, and “just in case” there are unexpected issues, I’m going to hold off assembling the wing box skeleton until I can do a trial fit of the outboard tanks. Subsequently, I’m going to fit and match drill the skins, then prime everything, and then start on the ailerons while waiting for the fuel tanks to arrive.

I researched the issue of match drilling the skins before the wing boxes are riveted, and found cases where it had been done before. A side effect of this different build order is it will not be necessary to dimple the ribs after they’re already riveted to the front and rear spars, which makes life a bit easier. I reassembled the right wing, de-burred the various top skin edges, and cleco’d them in place. Everything seems to fit together well. The wings are large, and will take quite some time to match drill.

While thinking about all this I unpacked the aileron trim kit, and de-burred/drilled/scuffed all parts just to add more items to the priming collection.

  • w17a
    Wings torn down, rear spar parts de-burred
  • w17b
    Aileron trim kit
  • w17c
    Match drilling aileron trim kit against inspection cover
  • w17d
    Aileron trim kit parts de-burred, scuffed
  • w17e
    Right wing re-assembled, top skin fitted ready for match drilling