United States: Postal History 1933, Century of Progress Graf Zeppelin Flight group

United States: Postal History
1933, Century of Progress Graf Zeppelin Flight group,
of eleven covers, all franked with 50c green (Sc. C18), and bearing appropriate handstamped flight cachet, with Miami to Chicago (2), Akron to Chicago, Friedrichshafen to Chicago (dual USA/German cachet), Chicago to Friedrichshafen (3, one with some wrinkling), Friedrichshafen to Rio de Janeiro (some ink running) Akron to Seville, Spain, Friedrichshafen to Pernambuco, and Miami to Akron, with three commemorative covers related to the event, an attractive assembly, most very fine.
Cover