300mm Ducted Fan

This extremely large ducted fan was designed and built primarily for powering a jet scooter, but it has an array of other applications including go-karts or R/C aircraft. Styled after the Rolls-Royce Ultrafan, this absolute unit of a fan has 18 interchangeable blades and room for a powerful motor. The motor mounting plates ideally should be CNC or laser cut out of metal or carbon fiber due to 3D-printable plastics not handling well with heat. This project uses A LOT of filament (>900g) so beware that an entire 1kg roll may be used up.

Performance:
I use a 4Kw 170kv 6370 brushless motor on a 12s lipo battery to power this thruster, but more powerful motors may yield better thrust. The theoretical thrust of this unit (https://rcplanes.online/calc_thrust.htm) at 4Kw is in the range of 100N -120N with a large margin of error from simplifying the blade geometry. In actuality, it provides more like 80-90N due to various inefficiencies. For more power, a lower Kv motor can be used at a higher voltage such as this 4.6Kw motor: (search 120kv 6384 motor on amazon or similar site) Motor may become warm, so a cooling fan in the tailcone is strongly recommended. When stress testing the 3D-printed blades out of PETG, they each could handle about 50N of force on their centroid of loading before significant deformation and withstood more than I could measure radially. This gives a safety factor of about 5 with my highest thrust scenario.

Manufacturing the two hub plates:
The blade hub and motor plate file should be used as a template only and the DXF files are provided to make the two required plates. Services such as SendCutSend are available, but personal laser cutters and CNC mills work just as well. I uploaded the DXF files to SendCutSend and got them cut out of 2mm Aluminum, which works well for my performance levels.

3D printing:
I used PETG for the entire thing and printed parts on a Creality CR-10 and a Raiscube A8r. Some parts are very large and need 310mm x 310mm bed space The CR-10 works well for this but those with smaller printers and modeling skill may need to separate it out into smaller sections. The main blade portion was originally one piece, but it failed enough times to warrant printing the blades individually.
Here are the parameters for the different pieces:
300mm housing - 1.6mm wall - 1mm top/bottom - 20% cubic infill - no support
single blade - 1.6mm wall - 2mm top/bottom - 40% cubic infill - use support and brim
top & bottom blade hub - 1mm wall - 100% infill - no support - brim optional
nose & tailcone - 1mm wall - 1mm top/bottom - 20% cubic infill - no support
Nozzle - 1mm wall - 2mm top/bottom - 20% cubic infill - no support
balancing weight - 1mm wall - 100% infill adjust z height to achieve proper balance weight

horizontal expansion - blade hubs may need negative horizontal expansion to have the blades fit snugly into the slots but they can't have a loose fit or the locking teeth won't engage.

final notes:
assembly can be complicated with so many parts. be patient and use sandpaper to adjust tolerances between interlocking parts. hasty assembly leads to damaged or cracked parts.
do not spin the rotor over 13,000 RPM or else it might suffer a sudden kinetic disassembly. Do not let any loose objects or body parts to come in contact with spinning blades or serious injury can occur.
Improper printing or use of damaged parts can also lead to catastrophic failure - inspect all parts before assembly and use.