Ultra micro
From EFlightWiki
Ultra micro models are those that are smaller than 'micro' models. For helicopters this generally means significantly smaller than 300-sized (250mm rotor length). For fixed wing the term is less clearly defined, but often means a wingspan of approimately 16 inches, which can sometimes be flown in a large gym/sports hall, with the space required dependant on the wing loading.
Examples include:
