The 3D Printed “Dummy” Radial Engine

I love “Golden Age” aircraft which means that I also love a radial engine. I cannot stand that flimsy vacuum formed piece of plastic they provide with kits to represent the awesomeness that is supposed to be inside that round cowl. Back in the old days, I used to make radial engines out of balsa. Now, I draw them in AutoCAD Fusion 360 and print them on my printer.

Draw it with the highest level of accuracy possible

AutoCAD Fusion is pretty incredible. As mentioned in a previous article, I happen to be an engineer with a certain level of design capability. I also have learned a little bit about what prints well and what doesn’t on the 3D printer.

The replica Pratt and Whitney Radial Engine

When you are designing for printing, take these tips into account.

  1. Plan on assembly with glue. It would be impossible to print the entire model in one print due to design consideration as noted below but mostly because the radial is 295mm across and my printer can only do 250 x 210 x 210mm parts.
  2. The parts were each designed to maximize the resolution of detail.
  3. Each component was designed to eliminate overhangs so supports were not needed.
  4. Although a few components could have been printed together, they were not so that a different color of filament could be used.
  5. I modeled the motor and the motor box so that the supports could be designed in.
  6. Some of the parts needed to be split (Exhaust Ring) so that they could be printed in two pieces.
  7. The pushrods will be made from 1/8″ aluminum tubing.
  8. The parts were broken down as follows and took about 50 hours:
    • Cylinders (9) of them – Black ASA Filament – 3 hours each.
    • Cylinder Bolt Rings (9) of them – Copper PLA Filament – 5 hours.
    • Case Ring / Nonagon (9 sided polygon) – Black ASA Filament – 4 hours.
    • Face Dome – Silver PLA Filament – 5 hours
    • Exhaust Ring – Copper PLA Filament – 4.5 hours
    • Spark Plug Ring – Red PLA Filament – 3 hours
    • Supports (3) to attach to motor box – 2 hours
The parts and pieces ready for assembly

The bulk of the assembly was as simple as busting out the Welders glue and assembling. I put the parts on a piece of wax paper and went to town. I used Aluminum tubing for push rods and placed some shrink tubing on the ends to look like the seals. Some 28ga wire did the trick for the spark plug wires.

And here is the finished motor during installation on the airplane.

The 3D printer is also awesome for making some jigs to align your radial. this would also be an awesome way for cowl alignment.

The temporary alignment jig was printed in Orange PETG Filament.

The Final Result:

Here is the final look with the cowl installed! Looks pretty awesome!

The Gilmore is ready to tear up the sky! Stay tuned for a review of the airplane!

1 thought on “The 3D Printed “Dummy” Radial Engine

  1. It looks great Ralph! Did you print the cylinders laying on their back? Any tips on getting the cooling fins to come out so well” they look to be about 0.6mm thick.

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