Extreme complexity is inherent to jet engines of all sizes, from those on a Boeing 777x to ones that power the smallest drone. While drones obviously need less turbo power than a jet, the microturbines that drive them remain a serious design and manufacturing challenge for engineers who have to cram all that complexity into a much smaller package.
The general rule of designing any jet engine is to keep it straight and round.
Whatever introduces variation into the dimensions of an engine is going to cut away at performance.
Drone microturbines, until very recently, have traditionally involved significant hand fabrication and many different piece-parts. Not only does this increase manufacturing and assembly costs, it leaves the engine more susceptible to performance variation.
Workarounds to fix such issues can result in design compromises, weight gain, and excess fuel burn. No wonder, then, that drone prices have remained high: a single agricultural- or military-size aircraft can cost between hundreds of thousands to many millions of dollars.
This state of affairs has created a window of opportunity for advanced metal-AM equipment manufacturers, who are experiencing an uptick in inquiries about the cost-effectiveness of printing an entire small turbine in the build chamber of a 3D printer.
Drone makers are taking their cue from commercial-aircraft engine manufacturers who have increasingly been using AM for part consolidation and lightweighting (witness advancements in 3D-printed engine components over recent years).