You may not have noticed, and most people will not, but a drone appeared in the records compiled by Guinness for the longest-duration flight of a quadcopter. Its development has been under wraps for the past couple of years, and its references to quite how it achieves this ranges from decidedly vague to non-existent.
I do patents, however, and have long done so and was thus able to glean some sort of insight from specification US11840329 filed by founder and CEO Brian Hinman. As with all quasi legal docs it is about as readable in parts as a phone directory but the crux appears to be this: it blends conventional helicopter technology with what makes an aerial drone.
In other words between the motor and rotor are (a) a planetary gear to reduce the RPM to allow for a larger and more efficient disk and (b) stepper motors to adjust the conventional cyclic and collective angle-of-attack of successive blades.
The project has followed the money... the patent picturing a piloted co-axial type of helicopter that nonetheless features the same tricks, since abandoned for a general-purpose quad able to hang around for surveillance or to haul heavy weights. As per how long it can fly for, the record relates to three hours underway, or two hovering.
The development therefore follows Colin's Law: avoid pioneering personal forms of flight if you want to avoid blogging in your dressing-gown for the duration.
P.S. I have forwarded this link to the company, SiFly, who'll shortly be asking WTF?
