Treaders,
We had a lengthy discussion with the CAA as to exactly which component of a Bell 47 constitutes the airframe as every single element is replaceable, unlike with a monocoque airframe.
Was it the bubble? (replaceable). Was it the tubular steel elements (all replaceable, singly or severally)? Was it the engine? Replaceable. Was it the floorboard? (replaceable). In the end we agreed that the only element that was really "the" helicopter was the brass plate. The skeg, painted with the G-reg was also replaceable, and was duly swapped over as the visible identifier.
A Stearman is also a tube frame structure, whose elements are all replaceable. Hence, I suspect that Ewald did something similarly legal and quite clever.