In a Facebook group I stumbled over this nice little picture:
Also there was a discussion about the type rating of this plane, especially if it classifies as a multi-engine plane. It is a Colomban Cri-Cri (MC-12/ MC-15).
What I've learned from the discussion and this document is, that this is an experimental plane and doesn't fall in the classic regulations and that UK's CAA doesn't require a multi-engine rating for the pilot. I think that answers the original question.
But in this thread and another discussion on another website I saw a lot of discussion about what regulations would apply if it would not be an experimental craft and what the FAA would say about it.
So my question is: There have to be specific requirements for a plane to require a multi-engine rating. To stay specific here, let's only look at the FAA. (I come from Germany, so if there would be any differences it would be interesting, but isn't required for this question)
Some people cited different paragraphs, but it seems none really applied and there was a lot of confusion. But I doubt that there is anything regarding aviation that is not tightly regulated, so I think there must be specific rules.
There is already a similar question regarding the Cri-Cri on this page here, but it has a different focus and it was stated that there would be no reason one couldn't file flight time in this plane as multi-engine flight time, but nothing precise.
So, what are the requirements for an airplane to be considered multi-engine and require a multi-engine rating to fly it? Also, why is this airplane considered single engine from a pilot perspective?
Note: I'm not a pilot, only a flight-simmer and aviation enthusiast.