Update: Finished testing and finished a full quad frame I'll link that in when I make a page, there is a updated duct that is slightly more efficient, stronger and much more rigid so I'll add that new one too, with a bracket and and without.
Hello this is a duct I have designed for use on small quadcopters, this has a bracket for bench tests, it takes highly inefficient 3inch prop and greatly increases the static thrust produced whilst reducing the current and the noise significantly,
It is designed around race star br 1306 3100kv motors but might suit other 12mm spaced motors, smoothing of the inside and lip is needed also the propellers will be tight to begin with and must be "shaved" to fit, to do this place a piece of sandpaper on the inside of the duct and carefully revolve the propeller over the sandpaper removing small amounts of material so a tight but free fit is achieved.
I have done lots of efficiency tests and posted it on RC groups if anyone is interested I was a little shocked myself: https://www.rcgroups.com/forums/showthread.php?3213985-3d-printed-3-duct-efficiency-tests-results
The plan is to make a full quadcopter using these ducts and 3 inch props, which I'm currently designing now or trying to lol.
Full finished pusher duct quadcopter 150mm sub 250g frame here https://www.thingiverse.com/thing:3498111
0.4 nib, single wall set to 0.5 thick, steeped infill, print with 1 layer height gap from top of support roof, a bit hotter than normal helps strength.
For extra strength (crash resistance) 0.4 line with two wall, if your parts are light you still be well under the 250 g