Recumbents and velomobiles are banned from international bicycling championships, because they are too fast. Many are tricycles and therefore technically not bicycles. Is it on-topic to ask questions related to tricycles, recumbants and velomobiles on the bicycles stack-exchange?
Generally yes - questions about wheeled vehicles operated by pedals are generally acceptable regardless of whether said vehicle has 1, 2 or more wheels and irrespective of how you sit on the vehicle.
That said, you will still need to make sure that your questions have a broad enough appeal and meet the other condition of the FAQ.