There's also been a few people building monocopters with a fixed, non tilting motor and prop, and four servo motor actuated fins at the bottom that can be used for thrust vectoring and to counter rotational forces.
Quadcopters that are designed for 45 min to 1 hr loiter time carrying a useful payload, while not being too big for a person to move around seem to be converting on 15 to 18 inch size prop and motor and esc combinations carefully chosen for optimal grams/watt thrust.
I've built a whole slew of drones over the last couple of years, quadcopters are hard to beat on many axis. But I have some proof that it may be possible to do substantially better with a monocopter in terms of efficiency. The hard problems you will then have to solve are payload attachment because unbalance is very tricky to deal with (whereas that is trivial in a quadcopter) as well as transitioning to level flight so that you can make good forward speed.
And what can be learned from full-scale classical helicopters that frequently carry underhanging payloads?
(I don't at all wanna be the typical HN person who thinks their questions about a field they know nothing about are in any way insightful. I'm just trying to learn.)
For a fixed payload it is indeed possible to set up the balance beforehand, even then you will probably end up with a drone that will translate slower or faster depending on the inbalance instead of hovering in place.
https://www.google.com/search?client=firefox-b-d&q=darpa+lif...