I too have been dreaming of building an experimental amateur built (EAB) eVTOL similar to the one described in the original post by dapug. I was especially glad for the clarification provided by Joda on the Experimental certification category. But the main stumbling block seemed to me to be the problem of category rating. 14 CFR 61 deals with certification of pilots, and it does list the various categories requiring category ratings. This list (§61.5) includes “Power Lift”. 14 CFR 1.1 defines “Powered-Lift” as:

Powered-lift means a heavier-than-air aircraft capable of vertical takeoff, vertical landing, and low speed flight that depends principally on engine-driven lift devices or engine thrust for lift during these flight regimes and on nonrotating airfoil(s) for lift during horizontal flight.

I believe that this is exactly the aircraft referred to by dapug. But §61.31, which deals with “type rating requirements”, says
(d) Aircraft category, class, and type ratings: Limitations on operating an aircraft as the pilot in command. To serve as the pilot in command of an aircraft, a person must—
(1) Hold the appropriate category, class, and type rating (if a class or type rating is required) for the aircraft to be flown; or
(2) Have received training required by this part that is appropriate to the pilot certification level, aircraft category, class, and type rating (if a class or type rating is required) for the aircraft to be flown, and have received an endorsement for solo flight in that aircraft from an authorized instructor.

This section made me stop thinking about this project. It seemed too daunting to try to get a Powered-Lift category rating—I couldn’t exactly rent time in an Osprey! But this thread made me look a bit deeper, and I think there is a solution. §61.31(l) says:

(l) Exceptions. (1) This section does not require a category and class rating for aircraft not type-certificated as airplanes, rotorcraft, gliders, lighter-than-air aircraft, powered-lifts, powered parachutes, or weight-shift-control aircraft.
(2) The rating limitations of this section do not apply to—
(i) An applicant when taking a practical test given by an examiner;
(ii) The holder of a student pilot certificate;
(iii) The holder of a pilot certificate when operating an aircraft under the authority of—
(A) A provisional type certificate; or
(B) An experimental certificate, unless the operation involves carrying a passenger;
…
(1) seems to say that any non-type-certificated (i.e. experimental) aircraft does not require a category rating.
(2) (iii) (B) reinforces this BUT adds the confusing “unless the operation involves carrying a passenger”. This seems to imply that at least some experimental power lift aircraft (two seaters) would require a category rating. The second paragraph seems to contradict the first.

I would love to hear from someone more well-versed in aviation rules than I. At any rate, it seems that a single seat experimental powered lift aircraft would NOT require a Powered Lift category rating, and possibly a two-seater would be exempt as well.

On a related note, I would love to join a discussion on the technical aspects of experimental Powered Lift aircraft. Are there forums either here in EAA or elsewhere dealing with batteries, motors, thrust, etc?