I love the propeller theme (no coincidences). Many people - even engineers - have never had a simple explaination of the theory behind propellers. These are the three-blade 29” propellers I currently have installed on Version 7.2.0 https://www.getfpv.com/propellers/commercial-industrial-propellers/tiger-29x9-5-carbon-fiber-three-blade-prop-pair.html
A propeller is an airfoil structure specialized for rotary movement. Because the distance of travel around a circle is greater at points further from the central mount, a propeller blade is optimized for different air speeds along its length - a key distinction from a wing, which is subjected to much more consistent airflow along the leading edge from the root to the tip.
Propellers with more blades produce more lift by a multiple, with losses. Each tip has lost energy as well, but nesting the propeller into a duct can reduce these losses. This is because the duct allows for a greater sustained pressure differential over the disk that represents the rotating propeller. It is this pressure profile, when multiplied by the area of the disk, that is used to estimate the total thrust.
While these wonderful Tiger Carbon Fiber propellers will do for now, the initial profits of the company will go towards designing custom propellers and deep cycle LiPo batteries to further optimize the efficiency of delivery in subsequent drone models.